THERMODYNAMIC SYSTEM WITH CLOSED CYCLE, WITH REGENERATIVE REFRIGERATIONS TO COUNTER CURRENT, TO GENE

专利摘要:
Thermodynamic system with closed cycle, with regenerative countercurrent cooling, to generate mechanical energy in one or more axes, from external flows of hot fluids, which consists of a cycle of mechanical power generation, clockwise development in a pressure diagram (in ordinates) temperature (in abscissa) with a heating phase in an exchanger thermally fed by an external fluid, a phase of multiple expansions in cascade of single-stage turbines, and a compression phase in multiple single-stage compressors, and which also consists of a heat-repair cycle, which counter-current cools the compressor diffusers, parallel to each other, and sequentially cools the turbine nozzles, regeneratively, recovering that heat in the hot focus. (Machine-translation by Google Translate, not legally binding)
公开号:ES2776024A1
申请号:ES202030181
申请日:2020-03-03
公开日:2020-07-28
发明作者:Penalosa José María Martinez-Val
申请人:Universidad Politecnica de Madrid；
IPC主号:

专利说明:

[0002] COUNTERCURRENT REGENERATIVE COOLING, TO GENERATE MECHANICAL ENERGY IN ONE OR SEVERAL AXES, FROM
[0003] TECHNICAL SECTOR
[0004] The invention falls within the field of thermodynamic cycles that transform thermal energy into kinetic energy of the axis of rotation of its expanding machine or turbine, in this case taking advantage of the heat of a flow of a hot fluid, which may have been created for this purpose. , or it can be residual or discarded from a thermal energy installation.
[0006] The invention includes a totally new thermophysical concept, which we call the heat repair cycle, which incorporates countercurrent regenerative intercooling.
[0008] TECHNICAL PROBLEM TO BE SOLVED AND BACKGROUND OF THE INVENTION
[0010] The problem consists of devising a system that uses thermal, compression and expansion machines to generate mechanical energy, useful for other purposes, on the axis of one of the latter machines, that is, a turbine or expansion machine.
[0012] The starting energy source is a fluid flow that has a temperature well above that of the environment. In particular, it can emerge from a facility escape; and in the situation prior to the application of this invention, that source was a zero value waste heat.
[0014] In order to extract useful energy from said energy source, the thermal fluid currents that are at our disposal, whether natural or artificial, have to be properly managed, with which a closed thermodynamic cycle is activated, which is presented in this invention. These currents that are at our disposal are:
[0016] - The one used to heat the hot spot of the cycle, in such a way that the energy is captured by the working fluid, in conditions to be exploited thermodynamically.
[0017] - The one used to cool the cold focus, which comes from the environment, either from the atmosphere or from the hydrosphere. This stream may have limitations of use, especially if it comes from a lake or a river with little flow, but these limitations can and should be included in the prescriptions of the application of the invention, in each specific case. In general, it will be possible to have the necessary cooling capacity, although it is important to minimize this, due to the limitations it may have. However, this source of heat extraction must be used as best suited to achieve the desired effects.
[0019] There are a variety of thermodynamic cycles devised to work with various types of hot spots. In the case proposed here, the thermal input comes from outside (it is not generated internally in the cycle). This means that there must be a heat exchanger that transfers the heat from the waste heat stream to the working fluid of the thermodynamic closed cycle in which the mechanical energy is going to be generated.
[0021] Similarly, a stream of a cold fluid (air, water, ...) will be necessary to extract all the heat not converted to mechanical energy, in such a way that the working fluid is restored to its initial conditions of the cycle. This part of the cold spot is more routine, as it is essential in practically all cycle applications (except in some unusual situations, such as artificial satellites, in which the cooling of cold spots is done by radiation emission). However, this cold fluid must be assigned other thermodynamic functions, if they contribute to optimizing the desired objective.
[0023] From the theoretical point of view and analysis of proposals, the state of the art can be seen described in previous applications of the inventor of the present application. Specifically, patent ES 2427648 B2 deals with a Brayton cycle with ambient cooling close to the critical isotherm. Another document, with Spanish patent application number P 201731263, describes a cycle whose lowest enthalpy point has a temperature below the critical one, but its pressure is above the critical pressure. A third document is the Spanish patent with publication number ES2713123 (application number P201930136).
[0024] In the state of the art it is important to point out the existence of several documents on cycles to take advantage of residual heat, and specifically patent documents ES2528932T3 and ES2374874T3, specifically dedicated to "waste heat recovery" which is a family of inventions very close to this one. , but of which they are not precedent at all, as neither are the ES2401582T3, ES2447827T3 and ES2634552T3, although they deal with the same problem. A little closer are US8869531 and EP3420201, which deal with cascade cycles, but with different working fluids in each cycle.
[0026] Another fundamental thermodynamic concern is to improve compression, since it is the phase that ends up being especially burdensome in the energy balance, in order to achieve good performance.
[0028] It is well known that isothermal compression, which has to be carried out under very slowly maintained cooling conditions, gives better results than isentropic compression, which is nevertheless much faster, which in a power cycle is generally decisive.
[0030] To achieve an isothermal air compression, a common recipe, but not always applicable, is to add a few drops of water to the air, so that the heat generated is consumed in evaporation of the water. This is the case of documents US5839270, US8225606 and JP2010071273, the latter applied to a gas turbine, as well as MX2016006069, applied to an internal combustion engine. Foaming fluid compressions have also been proposed, as in US4027993. Other inventions or applications related to improving compression are CN20236015, FR3066227, US4249384 and WO2008134283, but none of them provide anything that can be considered a precedent of the invention claimed herein.
[0032] From these documents and the general bibliography, it can be extracted that gas cycles, without condensation, commonly called Joule-Brayton, can be classified into two classes, according to two criteria: one, referring to the shape of the circuit in which they are the cycle materializes, which can be open or closed. Properly speaking, the open circuit starts and ends in the atmosphere, which represent conditions that cannot be changed by design, which to a certain extent impairs the performance of the cycle; but allows it to be internal combustion, which is not feasible in a closed cycle, since the combustion products would immediately suffocate the circuit.
[0034] The second criterion refers to the temperature map established in the circuit; and the two classes of cycles that can be distinguished are, on the one hand, those that have a turbine outlet temperature that is higher than the compressor outlet temperature; and in this case, and speaking of closed circuits, it is elementary to think about transferring the heat that leaves the turbine with the pressure of the low isobar of the cycle, passing it to the current that leaves the compressor, which will be colder, but higher pressure, as it will be in the high isobar.
[0036] The other alternative is that the turbine exhaust is at a lower temperature than the compressor outlet, in which case, there is no possibility of heat regeneration (increasing the pressure).
[0038] In the case of open circuits, we have the property that the performance increases when the pressure ratio increases, but its limit remains in any case below the Carnot performance. In this, the working gas is usually considered to behave as an ideal gas, which is acceptable, since it is usually air, which is essentially nitrogen.
[0040] In closed circuits, with heat regeneration, the performance increases on the contrary, that is, when the pressure ratio is reduced; and it coincides with the Carnot performance, right at the limit, that is, when the pressure ratio is equal to 1. But in this case, there is no cycle, since the high and low isobars are the same; but the indication remains that the pressure ratio of the cycle must be reduced to reasonable values.
[0042] This leads to the use of high-performance, low-cost, single-stage, turbine-flow rate compressors and turbines for both centrifugal and centripetal turbines. In both machines, the gas flow rates that can be achieved are limited by the sonic block (it is not possible to penetrate the sound barrier at any point, although the most significant in this context, in each case, is the flow path by the notch of minimum straight section). These speeds are related to the difference in static pressures that are established between upstream of the machine, and downstream of it.
[0044] Regarding the latter, both machines logically have opposite regimes: in turbines, the inlet nozzles have to serve to greatly accelerate the working fluid, which will move the blades of the machine, to whose axis it will transmit a torque and an angular velocity ( and therefore a power). This power must be a considerable fraction of what it carried as thermal flux, but it will not be able to transmit all of it, as there will be two types of losses:
[0045] - The output kinetic energy, which can carry 20 or 30% of the energy charged from the nozzle. This kinetic energy can be used in a next nozzle, which feeds a next plate of blades, if a cascade of single-stage turbines is assembled to take advantage of the available thermal energy. At the outlet of the last turbine stage, at the outlet of a compressor stage, a large part of that kinetic energy can be recovered as static pressure, adding a mechanical recuperator to its exhaust, from which it exits at very low speeds, on the order of 1 meter per second.
[0046] - Thermal losses, generated by friction, in the very diverse situations in which the flow collides with the walls, or there is friction in the flow itself.
[0048] The result of these thermal losses is that the real pressure is always lower, at a certain point in the circuit, than the ideal pressure; and the temperature is always higher. This makes it essential to adequately characterize compressors and turbines, through a performance that takes into account all this phenomenology, to determine their performance. This performance must measure the result, of compression or expansion, with a definitive exit velocity (of the diffuser or horn that is available) that does not exceed 5% of that of the higher speed straight section, and it could even be reduce this limit quantity to 1%, since the best use of the excess kinetic energy is its conversion to static pressure, which is ultimately PV energy (pressure per volume).
[0050] In the case of the compressor, the performance will be the quotient between the useful power generated by the machine (on the fluid) divided by the energy source that It feeds the machine (in the case of the compressor, its motor, which we will assume electric).
[0052] In the case of the turbine, the efficiency is the power of the electric generator, divided by the thermal energy entering the turbine nozzles.
[0054] These performances can be factored into two performances: one that measures from the electrical part to the shaft (in one direction or the other, depending on whether it is compressor or turbine) and a second performance that goes from the shaft to the thermodynamic cycle, and in the analysis of This invention proposal is the second performance that will be mentioned (the other is typical of electrical machines, and today it is very high, above 96%).
[0056] In the thermodynamic evaluation of the cycle, therefore, the energy conversion to electricity, or from electricity, is not taken into account, but the performance refers to the power on the shaft, as a relevant quantity.
[0058] From principle, it is considered that the working fluid behaves sufficiently as an ideal gas in the thermodynamic domain in which the cycle is going to unfold, meaning that the real values of the state variables do not differ from the ideal gas values. by more than 5%.
[0060] Thermodynamically, the cycle will be governed by the following equations, which refer to the input conditions in a component, for example, a nozzle, characterized by /, and the output conditions, which carry the subscript e. The variables considered are:
[0061] Temperature (t)
[0062] Pressure (P)
[0063] Density (p) or its inverse, the specific volume, V
[0064] Speed (v)
[0065] Straight through section (S)
[0067] In addition, the specific work appears, both external, 5Wext done by a machine (negative) or on a machine (positive), as associated with friction, due to 5Wroza losses; and the contribution of heat from the outside also appears, 5qext, which is positive if it is contributed, and the heat generated by the friction, 5qroza, which is equal to the work done by the flow on the duct, to advance, 5Wroza.
[0069] Several previous variables can be joined in another, which can be very useful to deal with speed and temperature with a certain homogeneity, and specifically it is:
[0070] Enthalpy (H) and particularly Remanso Enthalpy, (H00)
[0072] The equations that govern fluid flow and its evolution are:
[0073] - Fluid equation of state (ideal gas)
[0077] - Equation of the transformation of the fluid. In some phases of the cycle there will be an isobar, or very similar situation, in which the pressure remains almost uniform, such as the passage through the plate of blades, both of the turbine and the compressor, or the passage through an exchanger. The other relevant transformation is the isentropic one, governed by the equation:
[0079] P i / P j = P e / P l
[0080] Where y is the quotient between the specific heats at pressure and at constant volume; and both can be generalized in the polytropic transformation, of equation
[0082] P i / P f = Pe! Pe
[0084] Where g is the polytropic coefficient, which coincides with and when the transformation is adiabatic, it is worth 1 for the isotherms, and acquires an intermediate value for the practical transformations, which have some cooling, being the isotherm the one that has the most, and being zero the cooling of the adiabatic.
[0085] - Flow continuity equation, or mass flow, m '
[0087] m'i = P ^í V ^í S ^í = m'e = peveSe
[0088] - First Law of thermodynamics
[0092] - Energy conservation
[0094] Or, alternatively, a linear combination equation of the two above
[0098] And alternatively, they can be used, for energy conservation:
[0099] - Definition of backwater enthalpy, and backwater temperature, T0o
[0101] H00 = H - v 2 = CpT - v 2 = CpT00
[0103] - Conservation of backwater enthalpy in a stream line (no heat input or work done, and other contributions, such as gravitational, are ignored)
[0108] The above equations are essential to correctly devise the performance specifications, but this is more physically relevant if we express the thermal conditions in kinetic form, specifically, as a function of the speed of sound, i / s.
[0112] That for ideal gas, it turns out
[0117] This allows us to introduce the Mach M number as a fundamental parameter that unites the mechanical with the thermodynamic, from which it can be found
[0122] This equation applies both to the point with subscript i and e, like any other, being H, T and M their properties. The backwater enthalpy has already been defined previously, from the complete knowledge of the thermodynamic data of a point in a stream line, the backwater point could be taken as the one with the lowest velocity, as long as it was M < 0.01; and if there is no such point, it is considered of virtual existence, since it is possible to continue operating with said concept as much as desired. And from this last equation and the relationships proper to an isentropic transformation, we have
[0127] , 2 ( rP - 1)
[0129] and - 1
[0131] This last expression gives the Mach number at the end of a pressure ratio expansion r, starting from almost zero Mach.
[0133] According to the aforementioned formal analogy, the previous equations work for any polytropic, changing the exponent to k, instead of y. Due to the usefulness of the concept of polytropic evolution, it is pertinent to show that it must be accompanied by heat transfer, with a medium that provides it (heat) or extracts it. This is: in adiabatic there is no heat transfer with the surrounding medium. Precisely for this reason it is also isentropic (As = AQ / <T> = 0; as the heat exchange is zero. The entropy s does not therefore vary in adiabatic ones, and <T> is the mean temperature on a logarithmic scale, in the transformation suffered.
[0135] Now, in all movement there is friction, and at any stage considered, there will be a contribution of heat to the fluid, which will increase its entropy, which in turn will be against the efficiency of the process. This is especially taken into account in the invention.
[0137] From the conservation equations, for the stationary case as we are always assuming, and admitting that the flow is essentially one-dimensional, and that x represents the variable along the stream line, we obtain
[0140] This equation implies a change of topology when M = 1, going from an inverse relation, due to the minus sign, between v and S when M <1, to a direct relation when M> 1; which ultimately leads to sonic blocking when M = 1, which requires that S have a minimum value at that point (which is a notch).
[0142] For each straight section S of gas passage, there is a coupling between its Mach number and the established flow conditions, which are
[0143] - The mass flow m '
[0144] - Backwater conditions (T0o, Poo or P0o)
[0145] - Backwater sound speed vs0o
[0146] - The type of gas (through and)
[0151] In particular, the so-called critical section, Sc, which may not exist, and be merely a virtual reference, has a lot of theoretical and calculus importance, and is the value of S where M = 1 is reached.
[0156] This straight section is taken as a reference for the calculations, since the backwater section cannot be taken, since at speed 0, or tending to 0, there corresponds a section tending to infinity. The relationship between straight sections is
[0161] The following table gives the values of the S / Sc ratio for the case of monatomic gases, as a function of M. It can be seen that large variations occur below a moderate value of Mach, which could be 0.1 . For values above 0.6, the slope is practically horizontal, which makes the required precision difficult.
[0162] M S / Sc
[0181] In a single-stage centripetal turbine, the conversion of thermal to mechanical energy is carried out in two phases that are carried out in two different bodies: the nozzle (or nozzles, arranged circularly) in which the fluid loses pressure and temperature isentropically ( in the ideal cycle), reducing the pressure by a factor r, while greatly accelerating the passage of the working fluid; and the impeller or plate of blades, in which a significant part of the kinetic energy of the fluid passes to kinetic energy of rotation of the axis of the impeller, and of the electric generator coupled to it.
[0183] In all this evolution, the fluid cannot exceed the speed of sound at any point, since if Mach = 1 is reached, the sonic blockage would occur, which apart from slowing down the fluid, would cause great energy losses. The passage through the nozzles to produce the acceleration of the fluid, consuming thermal energy, is accompanied by a very large increase in the Mach number, from Mm, which is practically 0, to Mx = 1 (in reality, somewhat lower, but they can the extreme values 0 and 1 are used for the theoretical formulation, in which the subscript M refers to the inlet in the nozzle, and the X represents reference to the exit of the nozzle and entry into the impeller or blade plate; in which the equations that follow are fulfilled:
[0188] The previous relationships are fundamental in this system, and they particularly limit the pressure ratio in a single stage, which would correspond to Pm / Px, which is a function of the adiabatic coefficient, and; and it is calculated, immediately, that the upper limit of r in a single stage, is 2.05 for Ar (monatomic); 1,893 for N2 (diatomic) and 1,825 for C02 (triatomic).
[0190] The previous relations constitute limits, since the Mach numbers used are not maintainable (with Mach 0, there would be no flow, and nothing would work).
[0192] In the plate of blades, the properly mechanical interaction occurs, in which the fluid transmits kinetic moment to the shaft, but the fluid still exits the plate with great speed (with Mach numbers not much less than 0.5 in many cases), and This specific kinetic energy can also be seen as dynamic pressure, which is transferred to static pressure P, in a diffuser, or diffuser horn, or mechanical recuperator, which in the energy accounting that is followed in this document, is included in the performance of the machine itself, which is not only what turns (the blade plate) but also the front mechanical conditioner (the nozzle) and the rear one (diffuser).
[0194] Two essential parameters in the description of the cycle are the pressure ratio, r, in each machine, compressor and turbine, and the adiabatic quotient, y. which is the quotient between the isobar and isochor specific heats. For simplification of writing, the coefficient p will also be used
[0195] The compressor performance will be denoted by ^{r | c} , which is measured by the ideal enthalpy increase in the compression isentropic, divided by the real increase, corresponding to the real outlet temperature, Tc which can be written T0 ( rP - 1 )
[0196] See TC ~ T 0
[0198] With this denomination, the specific work of real compression, Wcr is expressed as a function of the theoretical one, Wc, always measured in joules per kilogram, as well as enthalpy, which is always specific, that is, per unit of mass, and therefore expressed in J / kg. When these quantities are multiplied by the mass flow or flow rate, in kg / s, the corresponding power (kJ / s) is obtained.
[0200] For the compressor the expression
[0201] Wc T0 ( r - 1)
[0202] Wcr
[0203] Go go
[0205] Similarly, the turbine performance, represented by qt, is defined as the real decrease in enthalpy, divided by the ideal decrease, and is expressed as a function of the real temperature at its outlet, Tt, with respect to that of the turbine inlet, TM, and the theoretical output, r "pTM,
[0206] Tm Tt
[0207] Vt = Tm ~ r ~ PTM
[0209] The ideal cycle performance, taking the machines as a reference (and not the heat exchanges) can be defined as
[0213] where p is the Carnot quotient, TM / T0.
[0215] If in the previous definition the theoretical specific tasks of the compressor and the turbine are replaced by the realistic ones, which include the performance of these machines, the following expression is obtained
[0218] From this last equation it follows that to obtain a positive return in the real cycle, the following must be met:
[0219] r p <M cr] t
[0221] Logically, in every thermodynamic cycle, heat exchangers are necessary. In our case, two have already been identified: the hot spot, and the cold spot. These two, more classic ones, are analyzed first, and then the newest ones are seen.
[0223] In the analysis of the exchangers, the fundamental thing is the equality of the thermal power, according to the total enthalpy balance of one of the two fluids, the one that is chosen (which in our case is the working fluid, which is the fluid that is heat, if it is the heat exchanger of the hot bulb, or the one that cools, if it is the heat exchanger of the cold bulb) and according to the thermo-transfer equation, that is:
[0224] Q = m'CpAT = UAST
[0226] Q = thermal power exchanged
[0227] m '= flow or mass flow of the working fluid, which may be heating or cooling, depending on the exchanger of the hot or cold source;
[0228] Cp = specific heat at constant pressure of the working fluid, which has been assumed ideal, so it will be a constant value
[0229] AT = absolute temperature variation in the working fluid as it passes through the exchanger
[0230] U = global heat transfer coefficient. For thin-walled tubes, with the same film coefficient inside and outside, h, the value of U = h / 2
[0231] A = heat transfer area
[0232] 5T = mean logarithmic temperature difference
[0234] The thermal design of the exchangers to be incorporated into the invention is a scientific challenge of great interest, because the final integrated performance of the cycle does not depend only on the machines, but on the management of the heat; which will become evident in the following.
[0235] DESCRIPTION OF THE INVENTION
[0237] The system is made up of a series of physical elements that constitute a closed thermodynamic cycle with three differentiated phases, one of them with a double function, existing superimposed on these elements, other components and fluids acting countercurrently, which reduce the entropy generated by irreversibilities in the compression and expansion mechanical phases of the thermodynamic cycle.
[0238] The previous elements included in the invention are:
[0240] • at least one heat exchanger, where each heat exchanger comprises a primary circuit, with two inlet branches, the main one and the regeneration lateral branch, having an external fluid that, entering through the main branch, provides heat to the fluid of work, which circulates through the secondary circuit; while another external fluid provides heat to the secondary circuit, entering through the lateral regeneration branch;
[0241] • the end of said secondary circuit coinciding with the beginning of the first expansion nozzle, with strong acceleration of the working fluid, and entry to the first turbine, said nozzle being cooled, to extract the heat generated by thermodynamic irreversibilities in the nozzle , by an external fluid traveling countercurrent inside its corresponding housing;
[0242] • the cooling fluid emerging from the nozzle through a conduit that supplies it to the regeneration side branch of the primary circuit of the exchanger, already mentioned;
[0243] • while the working fluid that emerges from the nozzle itself enters the impeller or blade plate of the turbine, to whose axis it transfers a high fraction of the kinetic energy it carries;
[0244] • the first turbine exiting through the exhaust, either to enter the nozzle of the second turbine, if there is a series of turbines connected in a pressure drop cascade, or to enter a deceleration diffuser and increase the static pressure , before entering the cold focus;
[0245] • the cold source being constituted by a heat exchanger through whose primary the working fluid circulates, and through the secondary the ambient fluid that cools it;
[0246] • after which the working fluid enters the first compressor, whose outlet diffuser is cooled countercurrently, by ambient fluid, to extract the heat generated by thermodynamic irreversibilities in the diffuser;
[0247] • entering from that diffuser, either in the second compressor, if there is a concatenation of these in increasing pressure value, or in the secondary circuit of the exchanger mentioned in the first place;
[0248] the previous elements being configured to perform a closed thermodynamic cycle with the following three phases:
[0250] - heating of a working fluid, carried out in the heat exchanger, in which the working fluid reaches its maximum temperature, Tm, at a pressure Pm;
[0251] - expansion of the working fluid, in concatenated turbines, where the countercurrent cooling system extracts the heat generated by the irreversibilities in the acceleration of the flow, and sends it to the primary of the heat exchanger; Furthermore, each turbine has an exhaust manifold, which is attached to the inlet nozzle of the next turbine, in decreasing order of pressures, except for the last turbine, whose exhaust manifold serves as the entrance to the cooling element, or cold focus, prior to the first compressor;
[0252] - integrated cooling and compression phase, in which the cooling element is alternately intercalated with the compressor, with repetition of this cooling-compression sequence, a cold focus being configured as the set of refrigerations prior to the compressors; and furthermore, each of the compressors of the concatenated series that does the total compression, is embedded in a counter-current cooler, particularly in the outlet diffuser of each compressor.
[0254] With which, said countercurrent refrigerant actions make up what can be called a heat-repairing cycle, applied both to the compressor outlet diffusers, as well as to the inlet nozzles to the turbines, the diffusers being externally cooled by the ambient fluid, and the nozzles being cooled by a fluid that can be mixed with the external fluid that provides heat to the hot spot, the latter having a regenerative thermodynamic purpose, since the heat extracted from the cooling of the nozzles is recovered in a high fraction, as high pressure heat of the working fluid, using the heat exchanger for this. heating, in whose primary the heat extracted from the nozzles is injected, by the regeneration branch.
[0256] Particularly adapted to this invention, a centrifugal compressor is selected as the compressor and, as the turbines, a single-stage type centripetal turbines. The centrifugal compressor is made up of an inlet manifold, plus a turntable with blades, which rotates according to an axis attached to the plate, driven by an electric motor or other source of rotational energy, and also having a cooled diffuser in the exhaust, This diffuser being a conduit with an increasing straight section, according to the direction of the working fluid, where its flow slows down, passing part of the dynamic pressure to static pressure; and in addition a previous cooling sequence is carried out, prior to the fluid entering the corresponding compressor, and in said sequence the ambient fluid of the cold focus, cools the working fluid to the minimum temperature that can be achieved with said focus, denoting said temperature as T0; and analogously, the expansion is carried out in single-stage centripetal turbines, each one of which is formed by an externally cooled nozzle, in which the working fluid is accelerated, plus a turntable, with blades of centripetal geometry for the flow , rotating the plate with its blades jointly with the turbine axis, each axis being specific to each turbine, and each axis being connected to an electric generator, or to a mechanical transmission system to drive a common axis to several turbines, or to another energy generation application; and the cooling of the nozzles is also carried out in cascade, but countercurrent to the direction of the working fluid, the cooling fluid emerging from the upstream part of the turbine nozzle with the highest pressure, said cooling fluid being injected into the exchanger heating of the working fluid, through the lateral regeneration branch.
[0258] As a basic formulation of the invention, the compression chain is made up of m compressors that all provide the same compression ratio, which we denote by r, and with m turbines in the expansion phase, each one of them with a pressure ratio also of value r, fulfilling, in the case of ideal gas fluid, and perfect turbines and compressors, the following equality
[0259] Tlm = 101
[0260] the maximum pressure of the circuit, Pm at the inlet of the first turbine, and the minimum, P0, at the inlet of the first compressor, being also related by the relation
[0261] Pm = r mP0
[0262] pointing out that these relationships correspond to the ideal situation, of fluid with ideal gas behavior, and perfect machines and components.
[0264] A configuration variant does not require that there be the same number of turbines as compressors. In general, there can be m of these and n of those, but it has to be fulfilled in this case, where rc is the compression ratio of the compressors, and rt the pressure ratio in a turbine, and, 771 __ y, Tt
[0265] ’C ~’ t
[0266] and likewise it must be fulfilled
[0267] Tm = T0 ( rfrtnfí)
[0269] The alternative is that each compressor has its own compression ratio, different from the values of others. So we would have rc1, rc2,. , and similarly for turbines; and in this case, ideally it is fulfilled
[0274] The fluid must be a gas with ideal behavior, that is, with an equation of state that does not separate from the ideal gas by more than 5%. The possibility of using monatomic gases, such as argon, diatomic gases, such as nitrogen, or triatomic gases, such as carbon dioxide, has already been introduced in the description of the state of the art; that present important variations in the value of p, since it is 0.4 for monatomic ones; 0.286 for diatoms; and 0.222 for those with 3 atoms.
[0276] From the point of view of minimizing the number of turbines and compressors for a given application, the most recommended family of gases is the monatomic, and within it, for reasons of abundance and price, argon, although its heat Specific is low, having an atomic mass of 40, instead of the 4 of helium, which however is very expensive.
[0278] Although the invention is correctly explained with an ideal assembly, with perfect machines, the reality is that every machine has losses, depending on its nature, and this must be taken into account when evaluating the invention, and particularly when calculating its performance.
[0280] In the state of the art, the ideal and the real performance have been introduced, and it has been seen that the inclusion of the compressor and turbine performance produces an effect equivalent to reducing the Carnot quotient, going from p to p ', according to the next definition
[0281] F = mcVt
[0282] For a cycle with a single machine, plus heat regeneration, the condition for positive performance was
[0283] r p <ia] cr] t
[0285] But in the case of this invention, this relationship is not applicable, since there is no regeneration, since the heat is taken from a flow of fluid that must be used in its entirety, and that leads to covering all the expansive potential of the fluid. working, hot and at high pressure, using a concatenated set of turbines, which coherently covers the range of temperatures covered in the hot source, using a pressure range that perfectly matches the pressure drops required in the inlet nozzles to turbines.
[0287] In this concatenated set of machines, the effects of thermal losses, or increased entropy, are the usual ones: pressure loss and temperature gain. In this invention, this is manifested in that the exponent p, decreases in the expansion with losses, and becomes approximately P '
[0289] F = f or t
[0291] Which means that to lower a given step, between two temperatures, a pressure step, r ', is needed greater than the original r, since
[0292] r P = r 'P'
[0294] In the case of the compressor, it is the opposite, since the pressure is increasing, and the coefficient p is modified to P ', according to
[0295] F = P h c
[0297] In a turbine with efficiency r |, the relationship between the enthalpy given in the real case, AHr and the ideal one, AH, is:
[0298] AHr = CvTm { 1 - r-P ') = rjAHi = rjCpTm ( l - r ~ P)
[0300] At this point, thermo-repair is essential to keep the working fluid in the proper thermodynamic path, which for turbine expansion is adiabatic. Therefore, it is essential to extract from the working fluid the heat generated by irreversibilities, which is the complement of the useful enthalpy, that is:
[0305] Where the subscript i has been included in the pressure ratio, r, to denote that it would be the value of the ideal process, with performance 1. When in reality, the pressure ratio will be lower if the nozzle is cooled to remove the friction heat. The reduction of the pressure ratio is obtained from:
[0310] The following table shows r as a function of performance, (r, = 2)
[0311] r | r (ro = 2)
[0318] It should be noted that the cooling to be produced in the nozzle can and must be corroborated with the continuous measurement of the pressures and temperatures at the inlet, e, and at the outlet, s, of the turbine, which must comply
[0321] If the Ts is too high to fulfill that equation, it has to intensify the cooling, and attenuate it, if it is too small.
[0323] Compression is governed by a similar law, which leads to
[0328] The values of r in heat-repaired compression are shown in the following table, which gives values very similar to those of expansion.
[0329] H r (ro = 2)
[0336] As in expansion, in compression, the coherence of the evolution of the variables must also be monitored, with the thermodynamic evolution to be followed.
[0338] In compression, which is carried out at a much lower temperature than expansion, it is necessary to consider following a polytropic trajectory, even reaching the isotherm, which is the one that requires less compression work, but the most cooling.
[0340] The following table gives information on the relevant variables of this type of compression, as a function of its exponent g, which varies between the y of the adiabatic case and the value g = 1 of the isotherm. The working fluid is argon (R = 208 J / kg-K; Cv = 312 J / kg-K) where Cg is the specific heat of the polytropic (infinity for the isotherm, to be calculated by its own method) and energy items are in J / kg.
[0341] gr max T sup C g PdV Q ext -TC 2 2.0070 425.00 103.99 26000.52 12998.96 52001.04 1.9 2.0186 418.42 80.88 27368.97 9577.77 52001, 04 1.8 2.0318 411.11 51.99 28889.47 5776.45 52001.04 1.7 2.0472 402.94 14.84 30588.85 1527.91 52001.04 1.6667 2.0528 400 .01 0.00 31200.00 0.00 52001.04 1.6000 2.0651 393.75 -34.68 32500.65 -3251.69 52001.04 1.5000 2.0863 383.34 -104.02 34667.36 -8668.57 52001.04 1.4000 2.1118 371.43 -208.03 37.143.60 -14859.30 52001.04 1.3000 2.1430 357.69 -381.37 40,000.80 - 22,002.44 52001.04 1.2000 2.1822 341.67 -728.05 43334.20 -30336.11 52001.04 1.1000 2.2329 322.73 -1768.10 47273.67 -40184.99 52001 , 04 1.0500 2.2642 311.91 -3848.21 49524.80 -45812.92 52001.04 1.0100 2.2932 302.48 -20489.04 511486.18 -50716.46 52001.04 1, 0050 2.2971 301.24 -41290.08 51.742.33 -51356.85 52001.04 1.0010 2.3002 300.25 -207698.40 51.949.09 -51873.76 52001.04 1.0000 2.3010 300.00 52000.65 -52000.65 52000.65
[0343] It is important to note that the compression work, TC, is the same in all cases, but not all reach the same r, whose maximum corresponds to the isotherm. Hence, it can be chosen for the compression path, although it has the drawback of presenting the maximum required cooling value, Qext, whose negative value indicates cooling.
[0345] To cope with this high heat transfer requirement through the lateral area of the diffuser, it is necessary to either lengthen the diffuser, or distribute the working fluid flow between several thinner diffusers, in parallel.
[0347] Finally, regarding the effects of irreversibilities, the coherence between the drop in pressures in expansion, and the drop in temperatures, we must mention the next balance of temperatures, assuming m compressors and n turbines in the cycle, with r't being the realistic pressure ratio in the turbine
[0352] At the same time, there is the pressure level, which the compressors must also comply with, with a compression ratio r'c:
[0357] An important chapter of the invention is the sizing of the turbine nozzles, and the compressor diffusers, although these all start from the same temperature, T0, due to the prior cooling to which the working fluid is subjected, before of each compressor, and all the refrigeration-compression pairs have a similar behavior. On the contrary, in turbines the temperature of the working fluid decreases, as the thermal energy is converted into kinetic energy of the axis of rotation. This subject will be seen more appropriately when describing a preferred mode of carrying out the invention, but the dimensioning itself is the strict application of the equations that govern the behavior of the working fluid in this cycle, as described in beginning of explanation.
[0359] It should be noted that a fundamental novelty in this invention is the so-called heat-repairing cycle, which consists in that both the diffusers at the compressor outlets, and the nozzles, at the inlet to the turbines, are externally cooled, countercurrent, in order to to reduce or eliminate excess entropy caused by friction inside the duct, since such excessive entropy produces a strong loss of performance. Hence, the heat transfer part is fundamental in this invention, and for the said components, the invention provides some prescriptions that are defined below, together with mechanical considerations, which must be integrated together with the thermal ones, including the effect of mechanical stresses created by thermal gradients in the wall material of diffusers or nozzles. Bear in mind that the shape of these elements, and in particular the variation of the straight section as the streamlines advance, is the fundamental parameter for the conversion of kinetic energy into pressure. static, or vice versa, so that the invention must respect the precision of the measurements, with a design that accommodates innovations without compromising the sensitive points of elements as apparently simple as diffusers and nozzles, but which have an impact very important in cycle performance.
[0361] On the one hand, the prescriptions of the invention refer to the fact that the opening or closing of the passage of the fluid in these elements is not very abrupt, because if it is, a lot of manometric loss is generated. On the other hand, already in the first part of the explanation of the invention, it was specified that these elements are externally cooled, but it is necessary to avoid that this cooling causes appreciable changes in the geometry of the element, due to differential expansions in the same piece. With these prolegomena, the prescriptions are as follows:
[0362] - The diffusers and nozzles will be selected from conduits of revolution with a straight axis, or conduits with a circular straight section, or close to it, with an eccentricity of less than 10%, measured in excess of 1 of the maximum diameter over the minimum, and with warped or helical axis, passing said axis through the centers of the straight sections:
[0363] - the diffusers and nozzles will have a shaft length that will be greater than the highest value of the mechanical and thermal limits;
[0364] - the mechanical limit being that the length of the shaft is greater than twice the difference between the diameter of its straight section with the largest area, and the diameter of the one with the smallest area;
[0365] - and the thermal limit being an axis length such that, multiplied by the mean value of the length of the circumferences of the successive straight sections of the duct, gives a value of a surface that is greater than the value resulting from multiplying the thermal power to extract in countercurrent external cooling, by the thickness of the duct wall, and to divide said product by the thermal conductivity of the wall material, and divide all this by the number pi; - and the thermal power to be extracted in external cooling being a value equal to the power that is transformed from kinetic energy to pressure energy per volume, or vice versa, multiplied by said power transformed by the complement to 1 of the expected yield in said element, for said transformation, and divided by the value of the yield itself.
[0367] By means of this last limit, it is achieved that the temperature difference between the hot side and the cold side of the duct is limited to 1 ° C, and there are no stresses that deform the duct.
[0369] Also bear in mind that the cycle operates with a constant working fluid inventory. To do this, it is loaded with a certain number of moles, or kg, before starting a given work session, with known or expected characteristics. The total amount of working fluid contained in the closed circuit provides pressures and densities for a given temperature map. This map depends fundamentally on the thermal conditions of the fluid that carries the heat from the outside, so it corresponds to the hot focus, and depends on the environmental refrigerant, in the cold focus. The mole load therefore determines the pressure at each point in the cycle, which determines the thickness required in each conduit, so as not to exceed the applicable mechanical stress limits.
[0371] It should be noted that the hot spot is made up of a single exchanger, or several interconnected as one, and therefore the invention is explained with a single exchanger, through whose primary, or hot branch, the external fluid that provides the heat circulates, plus the heat regeneration fluid extracted from the countercurrent nozzles; and the cooler working fluid circulates through the secondary, which heats up. In the primary, the entrance of the regeneration fluid, through its branch, is made laterally, not through the face with the highest temperature, but at the level at which the fluid current of the primary reaches the temperature, descending, that carries the fluid from regeneration, at the end of its journey through the successive external cooling of the nozzles.
[0373] In the cold source, there are refrigeration exchangers for the working fluid, prior to the compressors, and all these exchangers are the same, since they perform the same function with equal flow rates of working fluid and ambient fluid, and the same values of temperatures of input and output.
[0374] Furthermore, each diffuser and each nozzle are embedded in a countercurrent circulating coolant casing; and said refrigerant is the ambient cold fluid itself in the diffusers, while in the nozzles, which are at a much higher temperature, a specific refrigerant is used, mixable with the heat fluid to be used, which constitutes the hot focus, selected said refrigerant between pressurized air or another fluid with similar physical characteristics, but with less oxidation capacity, and said specific refrigerant is injected laterally into the primary of the heating exchanger, at the level at which the temperatures of the original primary fluid, which enters through the main branch, and of the cooling fluid, which enters through the regeneration lateral branch, are equal, the pressures also being equal.
[0376] To unequivocally explain the prescriptions of the invention regarding the fundamental issue of heat transmission for one or another function, heating the working fluid or cooling it, the following temperatures are designated, corresponding, the first four, to the heat exchanger of the hot bulb, in which you have
[0377] -Tw, maximum temperature of the heat carrier fluid that feeds the hot spot
[0378] -Tm, maximum temperature reached by the working fluid, which is very close to Tw in the invention;
[0379] -Tu, temperature of the fluid that carries the residual heat, when it leaves the atmosphere, after having passed through the heat exchanger;
[0380] -Tc, temperature of the working fluid, when it leaves the compressor, which is the one with which it enters the secondary conduit (colder) of the heat exchanger;
[0381] and for what corresponds to the exchangers of the cold focus, we have:
[0382] -Tt, temperature of the working fluid at the outlet of the last turbine, which in a correct assembly of the invention, is equal to Tc; Hence, Tc is used in all the exchangers of the cold source;
[0383] -Tv, maximum temperature reached by the cooling fluid, which corresponds to its exit from the exchanger of the cold source;
[0384] -Ta, ambient temperature of the refrigerant fluid, with which it enters said exchanger from the cold source;
[0385] -T0, temperature of the working fluid, when it enters the compressor, after leaving the cold source;
[0387] The classical functionality of these aforementioned exchangers will first be analyzed; Next, the singularities of the cooling of diffusers and nozzles are exposed, and finally it is explained how to take advantage of the cooling fluids of said components, to optimize their role with regard to the performance of the cycle.
[0389] For each exchanger, the hot bulb and the cold bulb, two faces are distinguished: one hotter, where the hottest fluid enters and the coldest comes out, and the other face, which we call colder. All exchangers work countercurrently, and are designed with a possible imbalance between the heat capacity rates of one fluid in the exchanger and the other, the degree of imbalance being a concept developed for this invention, and which is fundamental in the hot spot, which is where residual or waste heat must be captured.
[0391] Said imbalance implies that on the hottest face of the hot bulb exchanger, the temperature difference between the hot flow, which is the residual, and is at Tw, and the cold flow, which is the working fluid, Tm, is very small; while on the cold side of said heat exchanger, the temperature difference, which corresponds to Tu minus Tc, can be much greater. This allows the working fluid to be heated to a value, Tm, practically the same as the temperature with which the residual heat is received, which is Tw, and that improves the performance of the cycle as such, since the higher Tm, the higher the coefficient g ( Carnot quotient). But for g to really be the highest possible value, in the exchanger of the cold focus, on its cold face, the difference T0 minus Ta must also be very small, which is achieved with an imbalance in this exchanger, analogous, but inverse to the previous one, since the exchange of the cold focus, on the hot side, will have a difference Tc minus Tv, which can be very high. Although it is admitted that the refrigerant fluid has zero value, and it does not matter to heat it more or less, sometimes there may be environmental and safety limitations that prevent Tv from being too high, which will restrict the field to select the level of imbalance that is adopted in that focus.
[0392] In the case of the hot spot, the temperature Tu marks the performance of capturing residual heat, since it is used from Tw to Tu, but not from the latter to Ta, which marks the environmental or neutral state, which is taken as an exergy reference. null. And its degree of equilibrium, cp, in the hot bulb exchanger, is defined as
[0397] and it is 1 for the case of the balanced exchanger.
[0399] And we define the degree of imbalance as the value complementary to 1, that is, 1 -cp, which is precisely 1 (cp = 0) when it is totally unbalanced (and the hot fluid does not change in temperature, but is a vapor that is condenses).
[0401] For the hot spot, calling the difference in temperatures on the hottest face, Tw-Tm, 0Oc, and 01c the difference on the coldest face, Tu-Tc, the mean logarithmic temperature difference, 5T, can be written as
[0402] 5T - l ^ c ~ 0 ^ c
[0403] ln (0lc / 0 Oc)
[0405] remembering that the transferred thermal power, Q, is
[0406] Q = m'CpAT = UAST
[0408] And from conjugating the enthalpy balance of the first part of the equation, with the thermo-transfer balance of the second part, we arrive at
[0409] 0ic = e oc exp ((l - cp) NUT )
[0411] where NUT represents the number of transmission units, defined by
[0416] For the balanced case, cp is 1, and the temperature difference between the hot and cold flow is always the same throughout the exchanger, which makes the system lose some performance, since Tm is somewhat less than Tw, which is which makes the effective temperature of the hot bulb lose On the contrary, the residual heat capture efficiency practically coincides with cp (except for the difference T0 - Ta) and the balance would be the best; but what matters is the total performance of the system, of which the catchment is a part, which must be multiplied by the performance of the corresponding cycle.
[0418] For the totally unbalanced case, cp = 0, and this is where the temperature difference is widest, from one face to the other; Although this case requires that the contribution of heat by the fluid that carries the residual heat, does it in a phase change, that is, by condensation, without a sensible change in temperature, which is a perhaps rare possibility, but that encompasses the invention.
[0420] In the fluid carrying heat from the outside, energy is all the more valuable the higher its temperature; But the low-temperature energy cannot be neglected either, since ultimately the working fluid must be heated from Tc to Tm, very close to Tw. Precisely what is important in this invention, with regard to heat exchangers, is that the difference between the temperatures of the coldest side, of the cold source, and the difference between the temperatures, on the hottest side, of the hot source , be very small. In the invention we prescribe that both 0Oc and 0Of be less than 5 ° C, taking 1 ° C as a reference value, for any application of this invention.
[0422] Given the equation
[0423] 0 ic = 80c exp ((l - ( p ) NUT )
[0425] which links the temperature difference on both faces, and the equation from the definition of 9,
[0427] 8 le = (T m - Tc) (1 - ( p )
[0429] The sizing of this component is prescribed by selecting a degree of imbalance (1 -cp) that together with the selection of the values of Tm and Tc leads to determining the NUT of the exchanger, which is
[0432] When the exchanger is balanced, an indeterminacy of type 0/0 appears, which is resolved by l’Hopital.
[0434] Analogously, we proceed with the exchanger of the cold focus, from whose balance of transferred enthalpy, we can write:
[0439] In this case, the cold stream is that of ambient cooling, and the hot stream is that of the working fluid, which is the one that changes the temperature the most, and therefore the one that conditions the exchanger.
[0441] Calling 0Of the temperature difference on the coldest face of this exchanger, which is T0-Ta, and 01f the difference on the hottest face, which is Tt-Tv, we can write the mean logarithmic temperature difference, 5T how
[0446] Remembering that the transferred thermal power, Q, is
[0447] Q = m'cCpc ( Tt - T0) = UAST
[0449] From conjugating the enthalpy balance of the first part of the equation, with the thermo-transfer balance of the second part, we arrive at
[0451] Qif = 0o / exP ((l - <Pf) NUT)
[0453] where NUT represents the number of transmission units, defined by
[0458] Note that, for the exchanger of the cold focus, the working fluid is the hottest, and hence the subscript c appears in this last equation, which is also the one that varies the most in temperature, so it is the one that has to intervene in the definition of NUT (and both the NUT itself as well as U and A refer to the exchangers, all the same, of the cold source, obviously different from the exchanger of the hot bulb, and without any direct relationship with it).
[0460] In the cold focus, from the definition of its degree of equilibrium, cpf of the cold focus, already expressed, we have
[0461] 6lf = {Tt - T 0) {l - c p f)
[0463] With which the sizing of this component is prescribed by selecting a degree of imbalance (1 -cpf) that together with the selection of the values of Tt and T0 leads to determine the NUT of the cold source exchanger, which is
[0468] But the essential question is the efficiency obtained in the exploitation of the residual heat carrier flux, whose available power, for heating, is WR WR = m! RCRpc ( Tw - Tc)
[0470] Note that the temperature has been limited below to Tc, and not to T0 or Ta (almost equal) because that cold tail of the hot external flow can no longer be incorporated into the working fluid, which below Tc has to be refrigerate.
[0472] In short, the power that is absorbed in the hot bulb is
[0473] WRc = m'RCRvc ( Tw - Tu) = m'Cp ( Tm - Tc)
[0475] where the last member (from the right) refers to the working fluid, whose mass flow m 'is defined precisely by the equation immediately above, and therefore depends on the choice of the outlet temperature Tu of the waste heat fluid. If this equates (practically, that is, with less than 5 ° C difference) to Tc, it can be said that the hot bulb absorbs all the technically available energy; and absorbs proportionally less, how much higher value has You. Therefore, a catchment yield can be defined, c
[0476] Wrc _ Tw Tu
[0477] £ c ~ W ^ ~ Tw - T c
[0479] To simplify some equations, and taking into account the prescriptions on temperature differences type 0O, which must be 1 ° C (less than 5 ° C, in any case), in these equations Tw can be replaced by Tm (and Ta by T0, in the cold). This leads to
[0484] There is no reason to limit the value of the collection performance, which can ideally be worth 1. For this, the hot bulb must be configured as a balanced exchanger, which may be more or less expensive, due to its larger or smaller size, which will the temperature difference between the residual fluid and the working fluid is smaller or larger. Hence, it can be admitted that said capture is optimized, and therefore the value of cp = 1.
[0486] The cooling of diffusers and nozzles through the wall of their ducts, which are externally bathed by a cooling fluid, remains to be explained. For the diffusers, the same refrigerant of the cold bulb is used. For the nozzles, the same cooling fluid is the ultimate sink for the extracted heat, but the cooling of the nozzles is carried out by an intermediate fluid, which also serves as a thermal regeneration agent. In all cases, it is a classic countercurrent exchanger, monotube, for which what is stated in the preceding paragraphs is valid for the cold source. A unique feature is that fins can be arranged outside the duct to improve heat extraction.
[0488] Once the elements that make up the invention have been presented, it is essential to end with a statement of the performance that these cycles can achieve, well idealized, well realistic.
[0489] The thermal power consumed by each compressor is:
[0490] W C1 = m'Cp( Tc - T0)
[0492] And the total thermal power consumed by the compressors is
[0493] Wc = mm'Cp ( Tc - T0)
[0495] In this last equation it is important to distinguish between the number of compressors, m, and the flow or mass flow, m '. In turn this equation can be rewritten as
[0496] Wc = mm'Cp T0 ( jP - 1)
[0498] To express the thermal power that the turbines deliver to the shafts, it should be noted that they act in cascade, for which the inlet and outlet temperatures in successive turbines correspond to what is given in the following table, in which, to simplify formulation, the following parameter has been defined:
[0499] T = r /
[0501]
[0503] And so on.
[0505] The total turbined power is thus a summation with n addends, as indicated below
[0510] Recalling the expression for the enthalpy balance in the cycle, the prescription is that
[0512] T _{1 C} = T _{1 rr}
[0513] T n
[0514] WT = m'Cp ( Tm - Tc)
[0515] Which also requires that the heat exchanger be balanced, with cp = 1
[0517] And the overall efficiency of using the heat supplied from the outside is, in terms of thermal energy of the machines
[0522] If the Carnot quotient is used
[0527] For what corresponds to WT, its expression is valid for the case of real machines with losses due to irreversibilities, since the heat generated by them remains mainly in the working fluid (it escapes a little due to the lubrication and the bearings). But irreversibilities require higher pressure ratios ( r ' instead of r) and this has an effect on increasing the energy consumption of compression, and also increasing Tc, which also has a negative effect on WT, although the expression is formally the same, but Tc and T0 are related in the realistic case by
[0528] Tc = T0r ’P h c
[0530] (where it has been assumed that there are the same number of compressors as there are turbines).
[0532] In the general case, of m compressors with performance qc and n turbines with performance qt, taking into account this last expression of Tc, the following set of equations can be written, at the end of which the thermo-mechanical performance is exposed:
[0533] Wc = mm'Cp r0 (r '/ / 7c - 1)
[0534] WT m CpTm ( one r n / ) t
[0536] WT - Wc
[0537] e R WT
[0539] Which can be written based on the fundamental parameters of the cycle
[0544] The influence of the type of gas on performance is evidenced through p, both in the ideal and in the realistic case, counting the performance of the machines. This is related to the selection of the working fluid, fundamentally its nature, which can be monatomic, diatomic or triatomic (with more atoms, the behavior is far from the ideal).
[0546] It was found that r, at one stage, cannot exceed 2.05 for argon, and other noble, monatomic gases; 1,893 for N2 (diatomic) and 1,825 for C02 (triatomic) for reasons of avoiding sonic blockage (not being able to exceed Mach number = 1). Expressed in r, with the corresponding exponent p (0.4 for Ar; 0.286 for diatoms; and 0.222 for triatomics), the maximum values of r for each type of gas are found, which leads to 1.332 for Ar; 1.213 for N2; and 1.14 for C02.
[0548] Apparently, the selection of the working fluid opts for monatomics, but if the ideal thermo-mechanical efficiency is calculated, for a given Carnot quotient, p, the same efficiency is obtained for any type of gas.
[0550] This is so, because in the formulation of the invention, there has been complete coherence between the pressure variations throughout the cycle, and the temperature variations, and this implies that, once p is given, the values are adjusted of r in such a way that the cycle is left with a perfect balance of pressure and temperature. But it should be noted that the values of r, logically, increase as p decreases, and this implies greater pressure jumps in each machine, which in general is more expensive and generates more losses. Even more, It may be the case that the value of r required to apply the invention exceeds the limit of the sonic block, and then the invention cannot be applied under those conditions; although there is a way to save it: increase the number of machines, which makes r decrease. The following table shows that for n = m = 2 the value of r for nitrogen, N2, goes beyond the limit, and for 3 machines of each type ( n = m = 3) it is just at the limit. The table corresponds to T0 = 300K, and Tm = 620 K (Carnot quotient p = 2.0667)
[0552] n (m = n) ideal r-Ar yield ideal r-N2
[0553] 2 0.309 1.831 2.337
[0554] 3 0.312 1.574 1.89
[0555] 4 0.313 1.438 1.664
[0556] 5 0.314 1.353 1.529
[0558] On the other hand, it is possible to set the number n of turbines fixed, and increase the number of compressors, in order to increase performance, but the effect of this possibility is very limited, as can be seen in the following table, for Ar and n = 3, with different values of m, with the same reference temperatures (same p = 2.0667) as the previous table. The effect of machine performance is also included, since the ideal case is shown in the central column (turbine and compressor performance equal to 1) and the cycle performance is given in the right column for a machine performance of 85%. The cycle performance drop is very strong. In fact, below 80%, the system does not work, as it presents a negative performance, as discussed below.
[0560] m q (c / t) = 1 n (c / t) = 0.85
[0569] For this, a last effect that must be exposed is going to be taken into account, and that is that of the maximum temperature Tm with respect to the minimum T0 of the cycle, that is, the Carnot quotient, p. The following table shows the results for argon, with two levels of this quotient, 2.0667 and 3. In this case, as indicated in the header of the table, 4 machines of each type are used, because if this is lower number, the case of p = 3 could not be covered, since it would require values of r above the limit of sonic block.
[0570] n = m = 4
[0571] n (c / t) p = 2.0667 M = 3
[0572] 1 0.313 0.44
[0576] Bear in mind that in the definition of the performance of the machines, the loss of energy that the fluid outlet velocity entails, which is usually the loss of the greatest contribution to the reduction of performance, in open circuits (where effectively it is lost, it escapes). In this case it does not escape, as it is used to give impulse to the fluid in the nozzle of the next turbine, in the expansion. And in compression, the exhaust velocity (which gives rise to the so-called kinetic pressure,% pv2) ends up transforming into an increase in static pressure, P, which is the mission of the compressor, therefore it is not a loss either.
[0578] The losses that must be accounted for are those that generate heat, which in turn remains within the fluid, but makes it difficult for its thermal energy to be transformed into kinetic energy, to be used in the turbine blade plate . Or vice versa, they generate more mechanical difficulty in the compressor blade plate. Therefore, when evaluating the thermo-mechanical performance of these machines, it is essential to take into account this definition of energy losses.
[0580] Finally, it is necessary to explain and characterize the most unique innovation of the invention, which is the heat-repairing cycle, which has two parts: the one relating to the cooling of the diffusers, in compression; and that of the expansion, in the nozzles.
[0581] For its analysis we will start from the equation
[0583] S q 8 q eX £ "one" ^ Q ro z a d H V d P
[0585] Which we complement with the following equations
[0590] d H = C,, d T P d V V d P
[0592] Which for the case without friction and without heat exchange, lead to
[0596] And rearranged gives
[0598] CvdT / T = ~ y d V
[0600] And integrating
[0601] TV 1-7 = constant = T 0 Vq ~ y
[0603] Which is the expression of an adiabatic, as was already known, and has been used in all of the above. The problem is that the appearance of 5qroza is inevitable, which causes the appearance of a polytropic of higher temperature, which we identified earlier by the exponent p / qc; which reduces cycle performance.
[0605] However, cooling the diffuser may lead to better results, which would have the high performance limit corresponding to isothermal compression. For this, the cooling must be very efficient, and the diffuser duct long enough, as already indicated. The minimum temperature at which isothermal compression could be done would be T0. Furthermore, dT = 0 would be fulfilled . The heat to be extracted would be governed by
[0607] 8 q e x t = P d V - 8 q ro z a
[0609] Which is negative (cooling) since dV is. And the mechanical work to be done is
[0610] rVs
[0611] Wu P d V = RT 0L n ( - V y s )
[0612] Jvt V¡
[0613] Which will be negative, that is, to be carried out by a machine, since the upper volume (at the end of the compression) is less than the lower one. Taking into account the equation of state, it can be rewritten as
[0614] Wiso = RT 0 L n ( l / r )
[0616] While for the ideal adiabatic case it is
[0617] Wadb = CpT0 ( rP - 1)
[0619] For a monatomic gas Cp = 5R / 2 the ratio between compression works remains
[0620] r Wiso / Wadb
[0630] The cooling of the diffusers produces a saving of a certain level in compression work, and a reduction in the temperature of the working fluid at the end of the compression, since in the isothermal case it is T0 and in the adiabatic case it is r ^ To. Both of these have a significant positive impact on full cycle performance, when heat-healing effects are included. However, the application of the invention can be done in different ways, depending on the cost that each item represents. For example, with argon as the working fluid, and for an ideal compression r = 2, the adiabatic requires a compression work of 49.8 kJ / kg, and the isotherm 43.3; but the saving of 6.5 kJ / kg in the latter requires cooling 43.3 kJ / kg (that is, 7 times more than the savings in mechanical energy, although it is true that cooling is easier and cheaper than compressing).
[0632] Regarding the cooling of the nozzles, a distinction must be made with respect to what has been explained for the diffusers, where the ambient cold fluid is carried excess heat. In the nozzles, the refrigerant flow, of air, for example, passes sequentially from low pressure to high pressure, heating up from Ta to a value close to Tm but below it, which we will denote with u> Tm, where u> a coefficient less than 1.
[0634] In this case, the ideal reference is adiabatic expansion, which, without cooling, presents an efficiency r | t that denotes that its complement up to one, divided by the efficiency itself, and multiplied by the total transformed power in mechanical energy, it gives the thermal power to be cooled, and injected into the primary branch of the heating exchanger. Although this heating is done in successive stages, one per nozzle, to assess its effect it can be done assuming heating all the way, corresponding to a pressure ratio rT equal to rn.
[0636] The theoretical temperature at the end of the expansion is Tc, and the real temperature is Tt, linked by the yield qt which corresponds to
[0641] The specific regenerative power to be extracted is
[0646] And this power in turn will have to be transferred to the heat-repairing fluid, which will require counting the absolute powers, which requires multiplying the specific powers by the costs (kg / s) corresponding to each fluid. For this we denote
[0647] m ’= flow of the working fluid of the closed thermodynamic cycle
[0648] m'R = expense of the external fluid that contributes the heat to the hot spot
[0649] m'g = expenditure of the regenerative flow of the heat extracted from the nozzles
[0651] As fundamental relationships we have, in terms of thermo-repair
[0652] m 'gCpg ( a) Tm - T a) = m' (1 - Ti t) Cp ( Tm - T c)
[0654] And in the heating exchanger the mixture is produced (not properly on the face of higher temperature level, but even lower level, to equalize temperatures between the main heating fluid and the regenerative fluid. This aspect is in a certain way secondary, and what is relevant is to establish the enthalpy balance in the said exchanger.
[0655] m'Cp ( Tm - T c) = om'gCpg ( a) Tm - T u) m'RCpR ( TR - T u)
[0657] Where a mixing performance, a, has been included to take into account the irreversibilities of that process. But if we take into account the last two equations, they can be combined, and we get
[0658] m 'Cp ( Tm - T c) = am' ( l - q t) Cp ( Tm - T c) m'RCpR ( TR - T u)
[0660] From which it follows
[0661] m'Cp ( Tm - Tc) (1 - cr (l - ti t)) = m'RCpR ( JR - Tu)
[0663] If there were no regenerative heat-repairing effect, the mass flow of the working fluid would be
[0664] m '= m'RCpR ( TR - Tu) / ( Cp ( Tm - T c))
[0666] However, with such an effect, it is
[0667] m! = m'RCpR ( TR - Tu) / ( Cp ( Tm - Tc) (1 - cr (l - qt)))
[0669] There is therefore an amplification of expenditure, and therefore of the power generated, which is
[0670] 1 / (1 - er (l - ti t))
[0672] The following table gives the amplification factor for various performances, of the nozzles on the one hand, and of the mixture in the primary of the exchanger, on the other. To condense the information on the effect, the same value is taken in each case for both returns.
[0674] a = r | -turb amplification
[0681] In addition to this effect, the cooling of the nozzle allows to achieve better performances in the acceleration of the working fluid, by reducing the temperature to the levels corresponding to the isentropic expansion, for which all the heat generated by irreversibilities must be removed, only. The heat extraction is intensified or relaxed so that the temperature at a monitoring point is equal to that required by the pressure value at that point. In this way, the accelerating expansion of the fluid reaches a Mach number similar to that expected, although some of the available energy has been lost in situ, but will be recovered in the hot spot.
[0683] The improvement is really substantial, although not all irreversibilities can be repaired by this thermo-repair. With it, the complete cycle is made up of:
[0684] - a compression phase composed of m compressor stages with cooled diffusers, making the conversion of kinetic energy of the working fluid to compression energy, and therefore from kinetic pressure to static pressure, follow a law that is determined by refrigeration which is applied, selecting the thermodynamic path between the extremes represented by an adiabatic compression, in which only the heat generated by irreversibilities is extracted, and an isothermal compression, with a constant temperature not less than T0;
[0685] - followed by a heating phase, in one or more exchangers, in the primary branch of which mix, at the same temperature, the fluid that comes from the counter-current cooling of the nozzles, and that that contributes the external heat, which enters the exchanger at a temperature higher than that coming from the nozzles;
[0686] - plus an expansion phase in a cascade of n turbines, each with:
[0687] - a nozzle in which the working fluid is accelerated, losing thermal energy, and carrying out external cooling that adjusts the value of the working fluid temperature to that of the isentropic one that ends with the outlet pressure, extracting the heat generated by irreversibilities, this heat going to form the thermal energy of a heat-repairing flow, which circulates countercurrent to the working fluid in the turbine cascade, and said heat-repairing flow being injected into the heating exchanger, as explained in phase above, so that this flow is counted as loss in the nozzles, and as thermal gain in the heating exchanger:
[0688] - there being then, in each turbine, a plate of blades, to which the kinetic energy of the working fluid is communicated, and makes the turbine shaft rotate, to which the electricity producing system is coupled;
[0689] - there being at the outlet of each turbine a connection manifold with the next nozzle, in decreasing pressure;
[0690] - until the end of the thermodynamic cycle of energy generation, which involves the final cooling down to the temperature T0, if it has not been reached;
[0691] - and as a consequence of the countercurrent cooling of the closed cycle of energy generation, already specified, an open and fractional cycle of heat repair is developed by cooling the compressor diffusers, using the cold ambient fluid that constitutes the cold source, in a set of open ducts, in parallel, one for each diffuser; and it also includes a series cooling circuit of the nozzles, starting with the one with the lowest pressure and ending with the one with the highest pressure, said flow being injected, at the end of its heating, into the heat exchanger that constitutes the hot spot of the system.
[0693] Finally, it should be noted the improvement that heat repair represents for the performance of the system, especially when the machines, compressors and turbines, present friction losses, and generation of entropy in general; as a consequence of which its own performance is less than 1. It was seen in the analyzes of the first presentation of the invention, that the performance of the system dropped a lot when the value of the performance per machine decreased a little, it being seen that in the base formulation of the invention, for a value of p = 2.0667, with 3 compressors and 3 turbines, working with monatomic gas, the performance with ideal machines was 0.311 and this dropped to 0.046 when the unit performance of the machines was 0.85.
[0695] The following table shows the cycle performance values for a value of g = 2.0667, with 3 compressors and 3 turbines, working with monatomic gas, with temperatures T0 = 300K, Tm = 620 K and with maximum flow temperature external hot spot of Tw = 645 K (corresponding to a quotient, emulus of Carnot, gw = 645/300 = 2.15). The performance of the first column is the performance of each type of process: compression, expansion (turbine performance) and heat recovery from the thermo-repair (the same value is taken, as indicated, for the three processes):
[0698] 1 1.28218775 0.726 1.15 0.48364152
[0699] 0.95 1.21807837 0.76421053 1.095375 0.41434928
[0700] 0.9 1.15396898 0.80666667 1.0465 0.33187034
[0701] 0.85 1.08985959 0.85411765 1.003375 0.23494899
[0702] 0.8 1.0257502 0.9075 0.966 0.12241222
[0703] 0.75 0.96164082 0.968 0.934375 -0.0068058
[0705] In this table it can be seen that the thermorepaired cycle improves ostensibly for ideal machines (since the overall performance of the cycle goes from 0.311 to 0.4836) and the result is more spectacular with real machines, since a unit yield of 0.85 was achieved previously, a system performance of 0.046 and with the heat repair it becomes 0.235. The change is radical, since it goes from not being usable, to having frank use. And bear in mind that in heat repair losses are not avoided, as each machine is affected by its performance. For this, it must be explained that the performance of the previous table corresponds to the most appropriate definition of system performance, which is
[0708] Where or was already presented as the regenerative recovery performance of the cooling flow of the nozzles, and the subscript R refers to the fluid that contributes, in the hot spot , with temperature Tw , the external heat to be used in the system. (It should be said that the last fraction, in Denomin, is practically worth 1).
[0710] BRIEF EXPLANATION OF THE FIGURES
[0712] Figure 1 shows a thermodynamic graph of pressure, P, in ordinate, in logarithmic scale, and temperature T in abscissa, in linear scale, in which the thermodynamic cycle of the invention is exposed, in its version of ideal machines, with 3 compressors and 3 turbines.
[0714] Figure 2 shows a graph similar to the previous one, but with compressors and turbines with thermo-mechanical performances of 90%.
[0716] Figure 3 shows the system of the invention, with a geometric and functional arrangement of the essential components of its thermodynamic cycle.
[0718] Figure 4 presents the same system, with the addition of the electrical elements that complement it, with a one-line diagram of the connection of the electrical generators driven by the turbine shafts. In this case, they are mounted in series, which allows the voltage to rise, at the cost of the sum of the currents generated having to pass through the windings of all the generators.
[0719] Figure 5 shows an electro-mechanical assembly with a single generator, driven by the three turbines, with axes parallel to the main one, by means of transmission belts.
[0721] Figures 6a and 6b show, respectively, the temperature diagram in the heat exchanger of the hot bulb, in an unbalanced case, and in a totally balanced case.
[0723] Figure 7 shows the temperature diagram of the heat exchangers of the cold source, which are prescribed to be unbalanced.
[0725] Figure 8 shows the thermodynamic cycle with thermo-repair. The power generation cycle is right-handed, while the thermo-repair cycle is left-handed, and is closed, in each of its branches, by the environment: there is a branch for each compressor, remaining in parallel with each other, and a single branch sequential on the turbine nozzles.
[0727] Figure 9 is a conceptual composition of components to materialize the cycle with heat repair of the previous figure.
[0729] Figures 10 a and 10 b show the H (enthalpy) P (pressure) schemes of the thermo-repair in compression and expansion respectively.
[0731] Figure 11 shows a countercurrent cooled diffuser.
[0733] Figure 12 shows a nozzle, countercurrently cooled.
[0735] Figure 13 shows the profile of the duct of a nozzle, in terms of radius as a function of the abscissa, which is where the axis of the duct unfolds, and also shows the Mach number of each section.
[0737] Figure 14 shows the profile of the duct of a diffuser
[0739] Figure 15 shows a multitubular mounting of a diffuser, to increase the lateral area of heat transmission in cooling.
[0740] To improve understanding of the explanation of the figures, the elements that make up the invention are listed below:
[0741] 1. Fluid flow that provides heat from outside the circuit, and enters the exchanger of the hot spot, through the main branch, with temperature Tw.
[0742] 2. Hot bulb heat exchanger
[0743] 3. Exhaust fluid flow (1) coming out of exchanger casing (2) with temperature Tu.
[0744] 4. Bundle of tubes of the heat exchanger, inside which the working fluid circulates, and constitutes the secondary of said exchanger.
[0745] 5. Grid-type plate to assemble the bundle tubes (4) in the diffuser (6) that channels the working fluid coming from the refrigerated compression phase. The fluid at this point has a temperature Tc, and a pressure Pm.
[0746] 6. Diffuser, with a flared shape of increasing straight section, which connects the end of the cooled compression phase with the heating of the working fluid in the hot spot.
[0747] 7. Plate, grid type, that leads the outlet of the bundle tubes (4) towards the first nozzle (8). At the outlet from the tubes, the fluid has a temperature Tm and a pressure Pm.
[0748] 8. Nozzle that feeds the first turbine (9).
[0749] 9. First turbine, higher pressure.
[0750] 10. Exhaust from the first turbine (9) which is in turn a nozzle for the second turbine (11).
[0751] 11. Second turbine.
[0752] 12. Exhaust of the second turbine (11) which is in turn a nozzle for the third turbine (13).
[0753] 13. Third turbine.
[0754] 14. Exhaust manifold of the third turbine (13), which leads the working fluid to the first cooler (15) of the cooled compression phase.
[0755] 15. First cooler, which is part of the cold bulb. Through the conduit (15e) that comes from the outside, enters the ambient cold fluid, with temperature Ta; and goes out through the duct (15s) with temperature Tv. In the other branch of the cooler, which goes from the exhaust (14) to the manifold (16), the working fluid is cooled from Tc to T0. Inlet manifold to the first compressor (17).
[0756] First compressor.
[0757] Diffuser of the first compressor (17) at the end of which, the temperature is Tc.
[0758] Second cooler.
[0759] Inlet manifold to second compressor (21)
[0760] Second compressor.
[0761] Second compressor diffuser (21) at the end of which, the temperature is also Tc.
[0762] Third cooler.
[0763] Inlet manifold to the third compressor (25).
[0764] Third compressor.
[0765] Electric generator coupled to the shaft of the first turbine (9) Connection cable with the external electrical load.
[0766] Connection cable between the generators of the first (9) and second (11) turbine.
[0767] Electric generator coupled to the shaft of the second turbine (11) Connection cable between the generators of the second (11) and third (13) turbine
[0768] Electric generator coupled to the shaft of the third turbine (13) Connection cable with the external electrical load, which is between the cable and the (27)
[0769] Electric motor of the first compressor
[0770] Electric motor of the second compressor.
[0771] Electric motor of the third compressor.
[0772] Disc fixed to the shaft of the first turbine (9) that moves the general shaft (38) through the chain or belt (37)
[0773] Chain or belt that links the shaft of the first turbine with the shaft of the single generator (41)
[0774] General axis of rotation of the single generator (41)
[0775] Chain or belt that links the shaft of the second turbine with the shaft of the single generator (41)
[0776] Chain or belt that links the shaft of the third turbine with the shaft of the single generator (41)
[0777] Unique electric generator.
[0778] Temperature trajectory of the hot external fluid in the heat exchanger.
[0779] Temperature trajectory of the working fluid in the secondary circuit of the hot bulb exchanger, in general.
[0780] Temperature trajectory of the hot external fluid in the heat exchanger of the hot spot, when the exchanger is balanced.
[0781] Temperature trajectory of the working fluid in the secondary of the hot spot exchanger, when said exchanger is balanced.
[0782] Temperature trajectory of the working fluid in the cooling exchanger.
[0783] Temperature trajectory of the cooling ambient fluid, in the secondary circuit of the cold source exchanger.
[0784] Path in temperature of the hot external fluid that thermally feeds the hot source of the cycle.
[0785] Temperature trajectory of the working fluid in the secondary of the hot spot exchanger, in which the working fluid experiences a quasi-isobaric heating.
[0786] Isothermal compression line, to which the thermo-repair of the upper compression stage tends
[0787] Counterflow cooling stream of the diffuser of said upper stage.
[0788] Path in the diagram (T; log P) of the realistic compression in the upper compressor diffuser, taking into account the generation of heat by friction, without cooling yet (51).
[0789] Symbol of the kinetic energy of rotation, delivered by the motor of the upper compressor, and which is mainly transformed into static pressure in its diffuser (line 52)
[0790] Overall cooling resulting from heat repair in the intermediate compressor diffuser.
[0791] Path in the diagram (T; log P) of the realistic compression in the diffuser of the intermediate compressor
[0792] Path in the diagram (T; log P) of the realistic compression in the diffuser of the lower compressor.
[0793] Symbol of the kinetic energy of rotation, delivered by the lower compressor motor, and which is mainly transformed into static pressure.
[0794] Symbol of the rotational kinetic energy, generated by the expansion in the lower turbine.
[0795] Path in the diagram (T; log P) of the realistic expansion at the upper turbine nozzle.
[0796] Resulting trajectory, in the diagram (T; log P) of the realistic expansion in the upper turbine nozzle, including the heat-repairing effect (61).
[0797] Countercurrent cooling of the upper pressure nozzle.
[0798] Overall result of heat-healing refrigeration (61) Connection for passing the heat-healing fluid, from the intermediate turbine to the upper one.
[0799] Symbol of the kinetic energy of rotation, generated by the expansion in the upper turbine.
[0800] Resulting trajectory, in the diagram (T; log P) of the realistic expansion in the intermediate turbine nozzle, including the heat-repairing effect (66).
[0801] Countercurrent cooling of the intermediate pressure nozzle. Symbol of the rotational kinetic energy, generated by the expansion in the intermediate turbine.
[0802] Countercurrent cooling of the lower pressure nozzle.
[0803] Resulting trajectory, in the diagram (T; log P) of the realistic expansion in the lower turbine nozzle, including the heat-repairing effect (68).
[0804] Connection, cooled in the cold source, of the lower pressure turbine exhaust, with the suction of the lower pressure level compressor (or first compressor)
[0805] Inlet of the cooling fluid of the nozzle heat-repairing circuit.
[0806] Casing for conducting the refrigerant fluid around the lower pressure nozzle.
[0807] Connection of the front casing (72) with the casing for conducting the refrigerant fluid around the intermediate pressure nozzle (74).
[0808] Casing for conducting the refrigerant fluid around the intermediate pressure nozzle.
[0809] Connection of the front casing (74) with the casing for conducting the refrigerant fluid around the upper pressure nozzle (76). Housing for conducting the refrigerant fluid around the upper pressure nozzle.
[0810] Lateral branch of entry into the heat exchanger of the hot spot (2). Said branch comes from the connection with the front casing (76).
[0811] Casing for conducting the cold ambient fluid, around the lower pressure diffuser.
[0812] Countercurrent cooling circuit of the lower pressure diffuser, which goes through the front casing (78).
[0813] Casing for conducting the ambient cold fluid, around the intermediate pressure diffuser.
[0814] Countercurrent cooling circuit of the intermediate pressure diffuser, which goes through the front casing (80).
[0815] Casing for conducting the cold ambient fluid, around the upper pressure diffuser.
[0816] Countercurrent cooling circuit of the upper pressure diffuser, which goes through the front casing (82).
[0817] Duct of a diffuser.
[0818] Entry of the working fluid into a diffuser, with high kinetic energy and low static pressure.
[0819] Output of the working fluid from a diffuser, with low kinetic energy and aita static pressure.
[0820] Straight section of the diffuser duct.
[0821] Cold ambient refrigerant shell that runs countercurrent to the working fluid.
[0822] Inlet of the cold ambient refrigerant that goes against the current of the working fluid, through the front casing (88).
[0823] Exit of the cold ambient refrigerant that goes against the current of the working fluid, through the casing (88).
[0824] One nozzle duct.
[0825] Inlet of the working fluid in a nozzle, with low kinetic energy and high static pressure.
[0826] Output of the working fluid from a nozzle, with high kinetic energy and low static pressure.
[0827] Straight section of the nozzle duct.
[0828] Housing of the heat-repairing coolant that goes through the nozzles countercurrent to the working fluid.
[0829] Inlet of the heat-repairing refrigerant that goes through the nozzles countercurrent to the working fluid, through the front casing (95).
[0830] Exit of the heat-repairing refrigerant that goes through the nozzles countercurrent to the working fluid, through the casing (95).
[0831] Cooling circuit, with ambient air, of the connection (70).
[0832] Connection of the cooling air of the circuit (98) with the fluid intake for cooling the nozzles (71).
[0833] . Initial point of compression.
[0834] . Friction lost enthalpy.
[0835] . Ideal compression path.
[0836] . End point of the ideal path.
[0837] . Real trajectory without thermo-repair.
[0838] . Ideally available enthalpy.
[0839] . Ideal pressure jump.
[0840] . End point of the heat-repaired path.
[0841] . Real pressure jump.
[0842] . Not used
[0843] . Initial point of expansion.
[0844] . Ideal path of expansion.
[0845] . Real trajectory.
[0846] . Friction lost enthalpy.
[0847] . End point of the ideal path.
[0848] . Ideally available enthalpy.
[0849] . Ideal pressure jump.
[0850] . End point of the heat-repaired path.
[0851] . Real pressure jump.
[0852] . Elemental diffuser of a multi-tube set
[0853] . Inlet of a diffuser
[0854] . Outlet of a diffuser
[0855] In Figures 6 (a and b) and 7 the following labels are used, which in turn correspond to those used in the text
[0856] Tw inlet temperature in the exchanger of the hot spot, of the outdoor hot flow (1)
[0857] Tm maximum temperature reached by the working fluid
[0858] Tu = temperature at which the outside flow (3) leaves the heat exchanger of the hot spot
[0859] Tc temperature that the working fluid exits, from the last compression stage Tt = exit temperature of the working fluid, from the last turbine (13)
[0860] Tv outlet temperature of the cooling ambient fluid, from the exchanger of the cold source, which corresponds to the label (15s)
[0861] T0 minimum temperature of the working fluid,
[0862] Ta = temperature of the cooling ambient fluid
[0864] In figure 12 the ratio D / Dc is used to represent the quotient between the diameter of the section of a nozzle, with fluid movement to the right, and the critical diameter, and in addition to giving the abscissa of the axis, x, as arbitrary units of length, the Mach number, represented by M, for each section is given.
[0866] MODE OF EMBODIMENT OF THE INVENTION
[0868] The invention is materialized by grouping in a circuit the successive components that have been prescribed in the invention, using materials suitable for the temperature and pressure levels that exist in each case. For example, for the heat exchangers of the cold source, which have temperatures moderately above the ambient temperature, it is possible to use aluminum or copper, due to their much higher thermal conductivity than carbon steel, in turn higher than that of stainless steel. Another important aspect in the selection of the material is its resistance to corrosion, although using a noble gas, such as argon, as a working fluid, internally the corrosion would be inhibited (even with the intrusion of water vapor). However, if CO2 is used as the working fluid, the intrusion of water vapor would generate carbonic acid, which could attack non-electrochemically protected materials.
[0869] But it is not possible to connect one component after another, without specifying its size, which has to be commensurate with the mass flow of the fluid, which in turn depends on the power at which it has to work. Said power can be measured in various phases of the cycle, each of them representing a different magnitude, although the power that matters most is the net power, which is the difference between the sum of the powers of the turbine shafts, and the sum of the powers absorbed by the compressors.
[0871] In each component, its associated power is the specific enthalpy exchanged, thermally or mechanically, (in J / kg), multiplied by the mass flow (in kg / s). And this value, the mass flow rate, is the key quantity in determining the straight through sections in the various couplings, which is the fundamental geometric variable of the design. In the case of nozzles and diffusers, so will their length.
[0873] These two components, and their countercurrent cooling for their heat repair, are the most specific of the invention, which can use compressors and single-stage turbines available on the market, but needs nozzles and diffusers that comply with the prescriptions of the invention. This section is especially dedicated to them, with more emphasis on the nozzles, due to their higher temperature and fluid speed.
[0875] The speed of the fluid plays an essential role in this system, and oscillates between two extremes: very low values in the exchangers, especially that of the hot spot, to limit its length, and in this we can find Mach values of 0.001; and values at the nozzle outlet, which will be close to Mach = 1. As all this refers to the speed of sound, which in this case is proportional to the square root of T, we find that the velocity profile is absolutely conditioned by the temperature profile. This is important when evaluating friction losses, which can be written as a function of its three main factors, in terms of the loss of manometric head: friction factor (f), which in turn can depend on speed, but in a much less than linear way; the geometric factor, (L / D) or in differential terms (dx / D) and the kinetic pressure pv2 / 2.
[0876] The power associated with the friction that causes this loss is the product of the previous loss due to the flow, and this leads to:
[0881] In the equation it can be considered that the v are fixed by the temperature map and the Mach number; and m '(kg / s) is due to the nominal power. That leaves Qroza independent of density, apparently, and yet it depends directly on L and inversely on D. To reduce this heat loss (which lowers performance, and also has to be cooled) it is advisable to go to large machines (high value of D) which leads to a low p, due to the constancy of the value of m '. And since the map of T cannot be touched in a given problem, this means that it is good to reduce the pressure P to reduce losses in this case.
[0883] This indication can be specified quantitatively with a fundamental design criterion for the heat-repairing cycle: the heat flow q '' (W / m2) must be less than a critical value, which is the one that can pass through the walls of the nozzles or the diffusers, when they are cooled countercurrently, without the temperature difference between the hot and cold side, ATP, producing ring voltages in the duct that exceed the maximum allowed, amax. These stresses are related to the coefficient of linear expansion, a, and to the above-mentioned temperature difference, so that if we call E the Young's modulus of the material, we have
[0885] ® m ax _ t tA T p
[0888] From which, ATP is limited, since the previous fraction must be of the order of 10-4, since the material is at high temperature, and as the coefficient of linear expansion is of the order of 10.5, the difference in temperatures between faces it must not exceed 20 ° C.
[0890] At the same time, it is necessary to remember the classical mechanical criterion that the thickness of the wall, the nozzle duct or the diffuser must meet
[0892] e> - ------- m to x
[0893] And it remains to apply that the criterion already mentioned that the heat flow does not exceed the critical value that is given by the difference in temperatures between faces, and the thickness, plus the conductivity k
[0895] q " = <- A Tv < two amax - ^ - A Tp
[0896] H nDL e v PD p
[0898] The above inequality is to be applied point to point, or straight section to straight section, in which the value of D is unambiguous. However, it can be stated, as has been done, in a rough approximation, with average values of D. Furthermore, the inequality can be written without being a function of this parameter but as
[0900] QvOZÍ ^{Z __n i a T}
[0901] P ^{^ 2 <7} m ax kA T p
[0902] 2nL kATp
[0903] (7r » ^<
[0904] Q ro za
[0906] The sizing of the high pressure nozzle of a circuit with argon, with 1 kg / s flow rate, and the following temperatures and representative data of its properties and coefficients will be considered:
[0907] Cp = 520 J / kg-K
[0908] R = 208 J / kg-K
[0909] Upper P = 0.4 MPa
[0910] r = 1.6
[0911] Tw = 640 K
[0912] T m = 620 K
[0913] T0 = 300 K
[0914] Ta = 290 K
[0916] The end of heating in the exchanger is chosen as the stopping point or backwater, with the values of 620 K and 0.4 MPa, corresponding to a density of 3.1 kg / m3 and sound speed of 463 m / s ; which means that a Mach of 0.001 represents 0.46 m / s which is an acceptable speed for the exit of the hot spot.
[0917] With the r selected of 1.6; the theoretical outlet temperature is 513.7 K and the Mach is 0.788; which multiplied by a speed of sound of 422 m / s gives 332 m / s of theoretical speed.
[0919] The theoretical converted energy is 55.28 kW, of which we assume that 85% is transformed into kinetic energy of the working fluid, and 15% into heat, which must be extracted, and is 8.3 kW.
[0921] This performance makes the muzzle velocity lower than the theoretical one, and in particular it is the square root of 2-0.85-55280 = 306.6 m / s.
[0923] To size the nozzle, it is necessary to start by calculating its extreme straight sections, which correspond to M = 0.001 and M = 0.99; and that give radii of 0.47 and 0.02 m respectively.
[0925] The reduction in radius along the nozzle is therefore 0.45 m; and proposing a classical geometric ratio in the suction cones of pneumatic machines, a value of the tangent of 0.25 is adopted; so the length of the nozzle would be 1.8 m. It may seem excessive, but in figure 12 it can be seen that it corresponds to a very proportionate profile, and the area of its wall is 1.5 m2. This makes its average thermal flux 5.5 kW / m2; which for a reasonable film coefficient of 100 W / m2K represents a temperature difference between the fluid and the inner wall of 55 ° C.
[0927] The most critical in terms of material occurs at the beginning of the nozzle, with a very wide mouth and the highest pressure (we have assumed 0.4 MPa). If a reasonable hoop stress limit, at that temperature, is 40 MPa, the above pressure is 1%; and taking into account that the radius is practically 0.5m, the thickness of its wall in that area should be not less than 0.005m. With this thickness, the temperature difference between the faces of the nozzle wall, with a thermal conductivity of its material of 20 W / mK (typical of an alloy steel) is 1.37 ° C, a figure with which no there is risk due to thermal stresses.
[0929] In the final part of the nozzle, the problem is quite another, and it is that with very little variation in diameter, there are important changes in the number of Mach. An increase of 1% of the critical straight section, implies a decrease from Mach 1 to Mach 0.9. And if it increases 4%, it drops to 0.8. The regulation of the step is done by the reason of pressures, not reaching the maximum allowed to reach M = 1, to avoid the sonic blockage. This reduces the risks of great overheating, which is what occurs in the blockage; and thanks to which the speed of sound increases at that point, which allows more expense (little more really) but at the cost of very strong irreversibilities, and therefore, loss of performance. It is preferable to reduce r, although that implies using some more machine, both compression and expansion.
[0931] On the other hand, the dimensioning and characterization of the compressors must be taken into account, governed by the same general equations, but applied just in the opposite way. In this case, the blade plate accelerates the working fluid to the required speed, which is mainly transformed into an increase in static pressure in the diffuser. This has less technical demands than the nozzles, because it works at a much lower temperature.
[0933] In explaining the invention, representative values were given for the various items involved, particularly the heat to be extracted and the compression work.
[0935] For the dimensioning of the diffuser, it is appropriate to take the outlet, of high pressure, as a backwater state, and in it the density will not be the same for all the compressors, but the higher the higher the Pa.
[0937] ^{_ p *} P00 _{K nij l i 0}
[0938] And the straight section of passage is
[0943] In this case, the speed of sound is always the same because it is isothermal,
[0947] That in this practical assumption, with T0 = 300K, there remains 322.5 m / s. In turn, with a pressure of 0.4 MPa the density is 6.4 kg / m3 and with an output Mach of 0.002 for example, you have a straight section of 0.242 m2, which is 0.278m in radius.
[0949] For the inlet, the straight section leaves 0.00086 m2 which implies a radius of 1.66 cm. The extension of the radius is 0.26 m, which suggests a shaft length of 1.04 m; with the previously used geometric recipe. Figure 13 shows the diffuser profile and its adjustment to the Mach number in each section.
[0951] Although these are less intense energy transactions than those that occur in the nozzles, the problem in the diffusers is that a lot of heat has to be extracted, so that the compression remains isothermal.
[0953] For example, the isothermal compression of 1 kg / mass flow of argon for r = 1.6 at 300K is 29.3 kW; and the adiabatic starting from that same temperature requires 32.76 kW; but another 29.3 kW of heat has to be extracted. plus friction losses, which can be 15% of 29.3 kW, that is, about 5 kW, which in total would mean 34.3 kW, which is a much higher amount than that calculated for the nozzle, which they were 8.3 kW, but in the nozzle it is not sought that the fluid evolves by an isotherm.
[0955] On the other hand, in the diffusers water can be used for cooling, at atmospheric pressure, which gives greater potential for heat repair. Furthermore, the flow of fluid to be compressed can be divided into a set of diffusers that in total offer a greater lateral area for heat transmission.

权利要求:
Claims (8)
[1]
1.- Thermodynamic system with closed cycle, with countercurrent regenerative cooling, to generate mechanical energy in one or more axes, from external flows of hot fluids, characterized in that it comprises:
• at least one heat exchanger (2), where each heat exchanger comprises a primary circuit, with two inlet branches, the main one and the lateral regeneration branch (77), having an external fluid (1) that, entering through the main branch provides heat to the working fluid, which circulates through the secondary circuit (4); while another external fluid provides heat to the secondary circuit, entering through the lateral regeneration branch;
• The end of said secondary circuit coinciding with the beginning of the first expansion nozzle (8), with strong acceleration of the working fluid, and entry to the first turbine (9), said nozzle being cooled, to extract the heat generated by the thermodynamic irreversibilities in the nozzle, by an external fluid traveling countercurrently inside its corresponding casing (76);
• the cooling fluid emerging from the nozzle through a conduit that supplies it to the lateral regeneration branch (77), which discharges into the primary circuit of the exchanger, already mentioned;
• while the working fluid that emerges from the nozzle itself, enters the impeller or blade plate of the turbine (9), to whose axis it transfers a high fraction of the kinetic energy it carries;
• the first turbine exiting through the exhaust, either to enter the nozzle (10) of the second turbine (11), if there is a series of turbines connected in a pressure drop cascade, or to enter a collector (14 ) of deceleration and increase of the static pressure, before entering the cold focus (15);
• the cold focus being constituted by a heat exchanger through whose primary the working fluid circulates, and through the secondary the ambient fluid that cools it, which enters through (15e) and leaves through (15s);
• after which the working fluid enters the first compressor (17), whose outlet diffuser (18) is cooled countercurrently, by ambient fluid, to extract the heat generated by thermodynamic irreversibilities in the diffuser;
• entering from that diffuser, either in the second compressor (21), if there is a concatenation of these in increasing pressure value, or in the secondary circuit (4) of the exchanger mentioned in the first place;
the previous elements being configured to perform a closed thermodynamic cycle with the following three phases:
- heating of a working fluid, carried out in the heat exchanger, in which the working fluid reaches its maximum temperature, Tm, at a pressure Pm;
- expansion of the working fluid, in the concatenated turbines (9, 11, 13), where the countercurrent cooling system (61) extracts the heat generated by the irreversibilities in the acceleration of the flow, and sends it to the primary of the heat exchanger hot; and also each turbine has an exhaust manifold, which is connected to the inlet nozzle (8, 10, 12) of the next turbine, in decreasing order of pressures, except for the last turbine, whose exhaust manifold (70) makes inlet to the cooling element, or cold focus, (98) prior to the first compressor (17);
- Integrated cooling and compression phase, in which the cooling element (15, 19, 23) are alternately intercalated with the compressor (17,21,25), with repetition of this cooling-compression sequence, being configured a cold focus as all the refrigerations prior to the compressors; Furthermore, each of the compressors of the concatenated series (17, 21, 25) that makes the total compression, is embedded in a countercurrent cooler, particularly in the outlet diffuser (6, 18, 22) of each compressor.
[2]
2.- Thermodynamic system with a closed cycle, with countercurrent regenerative cooling, to generate mechanical energy in one or more axes, from external flows of hot fluids, according to claim 1, characterized in that the compressor (17, 21, 25 ) is a centrifugal compressor, and the turbines are single-stage type centripetal turbines; where the centrifugal compressor is formed by an inlet manifold, plus a turntable with blades, which rotates according to an axis attached to the plate, driven by an electric motor or other source of rotational energy, and also having a diffuser (6, 18 , 22) cooled in the exhaust, this diffuser being a conduit of increasing straight section, according to the direction of the working fluid, where its flow slows down, passing part from dynamic pressure to static pressure; Furthermore, a previous cooling sequence is carried out in the corresponding exchanger (15, 19, 23), before the fluid enters the corresponding compressor, and in said sequence the ambient fluid from the cold source cools the working fluid to minimum temperature that can be achieved with said focus, denoting said temperature as T0; and analogously the expansion is carried out in the centripetal turbines (9, 11, 13) of the single-stage type, each one of them being formed by an externally cooled nozzle (8, 10, 12), in which the fluid of work, plus a rotating plate, with blades of centripetal geometry for the flow, rotating the plate with its blades jointly with the turbine shaft, each axis being specific to each turbine, and each axis being connected to an electric generator (26, 29, 31), or to a mechanical transmission system (37, 39, 40) to drive a common shaft (38) to several turbines, or to another power generation application; and the cooling of the nozzles is also carried out in a cascade, but countercurrent (61) to the direction of the working fluid, the cooling fluid emerging from the upstream part of the nozzle (8) of the higher pressure turbine, injecting said refrigerant fluid in the heating exchanger (2) of the working fluid, by the lateral regeneration branch (77).
[3]
3.- Thermodynamic system with closed cycle, with countercurrent regenerative cooling, to generate mechanical energy in one or more axes, from external flows of hot fluids, according to claim 1, characterized in that the compression chain is formed by " m ”compressors that provide the same compression ratio“ r ”for all of them; and existing in the expansion phase “m” turbines, each one with a pressure ratio also of value “r”, fulfilling, in the case of ideal gas fluid, and perfect turbines and compressors, the following equality

[4]
4. - Thermodynamic system with closed cycle, with countercurrent regenerative cooling, to generate mechanical energy in one or more axes, from external flows of hot fluids, according to claim 3, characterized in that for a configuration of the system with "m" of compressors and “n” turbines, and rc being the same compression ratio of the compressors, and rt the same pressure ratio in each turbine, it is true that

[5]
5. - Thermodynamic system with closed cycle, with countercurrent regenerative cooling, to generate mechanical energy in one or more axes, from external flows of hot fluids, according to claim 3, characterized in that for a configuration of the system with "m" of compressors and “n” turbines, it is fulfilled that:

[6]
6.- Thermodynamic system with closed cycle, with countercurrent regenerative cooling, to generate mechanical energy in one or more axes, from external flows of hot fluids according to claim 1, characterized in that the pressure drop in expansion, and the temperature drop, they fulfill the following temperature balance, assuming m compressors and n turbines in the cycle, and r't being the realistic pressure ratio in the turbine

[7]
7.- Thermodynamic system with closed cycle, with countercurrent regenerative cooling, to generate mechanical energy in one or more axes, from of external flows of hot fluids, according to any one of the preceding claims, characterized in that
- the diffusers and nozzles are selected from conduits of revolution with a straight axis, or conduits with a circular cross section, or close to it, with an eccentricity of less than 10%, measured in excess of 1 of the maximum diameter over the minimum, and with warped or helical shaped axis, said axis passing through the centers of the straight sections; - the diffusers and nozzles will have a shaft length that will be greater than the highest value of the mechanical and thermal limits;
- the mechanical limit being that the length of the shaft is greater than twice the difference between the diameter of its straight section with the largest area, and the diameter of the one with the smallest area;
- and the thermal limit being an axis length such that, multiplied by the mean value of the length of the circumferences of the successive straight sections of the duct, gives a value of a surface that is greater than the value resulting from multiplying the thermal power to extract in countercurrent external cooling, by the thickness of the duct wall, and to divide said product by the thermal conductivity of the wall material, and divide all this by the number pi; - and the thermal power to be extracted in the external cooling being a value equal to the power that is transformed from kinetic energy to pressure energy per volume, or vice versa, multiplying said transformed power by the complement to 1 of the expected performance in said element, for this transformation, and divided by the value of the yield itself.
[8]
8.- Thermodynamic system with a closed cycle, with countercurrent regenerative cooling, to generate mechanical energy in one or more axes, from external flows of hot fluids, according to any one of the preceding claims, characterized in that the complete cycle is composed of :
- A compression phase composed of m compressor stages with cooled diffusers, making the conversion of kinetic energy of the working fluid to compression energy, and therefore from kinetic pressure to static pressure, follow a law that is determined by the refrigeration that is applied, selecting the thermodynamic path between the extremes represented by an adiabatic compression, in which only the heat generated by irreversibilities is extracted, and an isothermal compression, with a constant temperature not less than T0;
followed by a heating phase, in one or more exchangers, in whose primary circuit the fluid that comes from the counter-current cooling of the nozzles is mixed, at the same temperature, and enters the primary through the regeneration side branch, and the one that contributes the external heat, which enters the exchanger through the main branch, at a temperature higher than that coming from the nozzles;
plus an expansion phase in a cascade of n turbines, each with:
a nozzle in which the working fluid is accelerated, losing thermal energy, and performing external cooling that adjusts the value of the working fluid temperature to that of the isentropic one that ends with the outlet pressure, extracting the heat generated due to irreversibilities, this heat going to form the thermal energy of a heat-repairing flow, which circulates counter-current of the working fluid in the turbine cascade, and said heat-repairing flow being injected into the heating exchanger, as stated in the preceding phase , so that this flow is counted as loss in the nozzles, and as thermal gain in the heating exchanger;
there being then, in each turbine, a plate of blades, to which the kinetic energy of the working fluid is communicated, and makes the turbine shaft rotate, to which the electricity producing system is coupled;
there being at the outlet of each turbine a connection manifold with the next nozzle, in decreasing pressure;
until the end of the thermodynamic cycle of energy generation, which involves the final cooling to the temperature T0, if it has not been reached;
and as a consequence of the countercurrent refrigerations of the closed cycle of energy generation, already specified, an open and fractional cycle of heat repair is developed by cooling the compressor diffusers, using the cold ambient fluid that constitutes the cold focus, in a set open ducts, in parallel, one for each diffuser; and it also includes a series cooling circuit of the nozzles by means of an external fluid, which begins its flow with the one with the lowest pressure and ends with the one with the highest pressure, said flow being injected, after heating, through the lateral branch of regeneration, in the primary circuit of the heat exchanger that constitutes the hot spot of the system.

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ES2776024B2|2021-10-28|

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ES2652522A1|2017-10-30|2018-02-02|Universidad Politécnica de Madrid|THERMODYNAMIC CYCLIC PROCESS WITHOUT FLUID CONDENSATION AND WITH PRESCRIPTIONS TAXED ON ITS POINTS OF MINIMUM AND MAXIMUM ENTHALPY AND DEVICE FOR ITS REALIZATION |ES2821746A1|2020-10-28|2021-04-27|Univ Madrid Politecnica|CLOSED CYCLE THERMODYNAMIC SYSTEM TO TRANSFORM THERMAL ENERGY INTO MECHANICAL ENERGY |

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ES202030181A|ES2776024B2|2020-03-03|2020-03-03|THERMODYNAMIC SYSTEM WITH CLOSED CYCLE, WITH COUNTERCURRENT REGENERATIVE COOLING, TO GENERATE MECHANICAL ENERGY IN ONE OR SEVERAL AXES, FROM EXTERNAL FLOWS OF HOT FLUIDS|ES202030181A| ES2776024B2|2020-03-03|2020-03-03|THERMODYNAMIC SYSTEM WITH CLOSED CYCLE, WITH COUNTERCURRENT REGENERATIVE COOLING, TO GENERATE MECHANICAL ENERGY IN ONE OR SEVERAL AXES, FROM EXTERNAL FLOWS OF HOT FLUIDS|