FR2568673A1 - Vapour compression heat pump circuit and method for supplying heat to a load making use thereof by means of this circuit - Google Patents

Abstract

The invention relates to a vapour compression heat pump circuit. In this circuit, a saturated liquid is expanded through a constriction 10 intended to produce a reduced pressure drop and whose output is connected to a modified evaporator 12 which comprises an atomising device 13 producing progressive pressure reduction in the two-phase liquid/vapour mixture leaving the constriction, with shared reduction in temperature and absorption of heat coming from a source 1 so as to produce the saturated vapour which is directed towards the compressor 5 of the circuit. Field of application: heat pumps.

Description

 The invention relates to a vapor compression heat pump circuit.

 The causes of irreversibility in conventional vapor compression heat pump circuits are numerous and lead to a limitation of the thermal efficiency of such a circuit. One of the main causes of irreversibility is the pressure reducer or throttling element, commonly used in place of a turbine for reasons of simplicity, which does not allow any recoverable work. Another cause results from the isobaric (and therefore isothermal) heat exchange in the vapor compression circuit, both in the condenser and in the evaporator.

 The invention aims to reduce the irreversibility of a vapor compression heat pump circuit.

 In accordance with the present invention, a vapor compression heat pump circuit is provided comprising a throttle in which a working liquid from the circuit condenser expands, the throttle being arranged so as to deliver a two-phase mixture liquid / vapor and being followed by an atomization device designed to gradually relax the two-phase mixture from the throttle, with a distributed reduction in temperature, to produce saturated steam intended to be compressed by the compressor of the heat pump circuit.

 According to another aspect of the invention, a vapor compression heat pump circuit is provided which comprises a throttle by which a saturated liquid is expanded so as to form a two-phase liquid / vapor mixture, an evaporator intended gradually expanding the two-phase mixture from the throttle, with a distributed reduction in temperature to produce saturated steam, a compressor for compressing the saturated steam to produce superheated steam, and a condenser for extracting heat, to supply it to a user load, superheated steam from the compressor to produce the saturated liquid intended for throttling.

 In accordance with another aspect of the invention, there is provided a method for supplying heat to a user load using a vapor compression heat pump circuit, which includes the steps of expanding a liquid working through a throttle to form a mixture of two liquid / vapor phases, gradually relaxing the mixture of two phases, with a distributed reduction in temperature and absorption of heat from a heat source to produce saturated steam, compressing the saturated steam to produce superheated steam, extracting heat to supply it to a user load, from a part of the circuit between the compressor and the throttle, and repeating these operations.

 Steam compression heat pump circuits are known in which a saturated liquid coming from a condenser is expanded through a shutter or throttle and delivered from the latter to the inlet of an evaporator where it is vaporized under conditions isothermal. However, in the invention, only limited expansion of the saturated liquid from the condenser takes place in the throttle and the remaining expansion occurs in the expansion means, with a distributed reduction of the temperature in order to reduce the irreversibility.

The improvement brought by the invention will now be explained more fully. Considering the case of an evaporator placed in the known heat pump circuit, heated by a fluid coming from an external heat source, the working fluid which circulates from the heat pump must be colder than the point cooler fluid from the heat source. The working fluid inevitably leaves the pressure reducing valve or the throttling element at a temperature which is significantly higher than that of the evaporator, whatever the heat exchangers incorporated in the circuit of the heat pump. . Consequently, the fluid passing through the throttle element partially vaporizes in order to cool down to the lower temperature of the evaporator. The less this cooling is intense, the less the loss of capacity of the circuit of the larger the heat pump, the higher its efficiency, and the invention makes use of this fact. It should be noted that the L / T vaporization entropy is lower,
L being the latent heat of vaporization of the working fluid and T its temperature.

We will now consider a numerical example. It is assumed that 3rd working fluid leaves at 300C from the throttle element. If, for example, the external fluid coming from the heat source arrives at 150C and is cooled to 50C in an isobaric evaporator, the temperature of the evaporator will generally be of the order of -50C. The increase in the entropy of the working fluid of the heat pump circuit, to the point of entering the evaporator, is therefore (without taking into account sensitive heat)
L (1/268 - l / 303) where L is expressed in joules. In the evaporator, the entropy of the working fluid increases by L / 268 per mole.

 Considering now the numerical evaluation of an equivalent embodiment according to the invention, the evaporator heat exchanger can function satisfactorily if the working fluid evaporates between 100C and -50C, instead of 'have the isothermal value of -50C.

At the entrance of the evaporator heat exchanger, the entropy produced by vaporization is not more than L / 283 per mole, gradually increasing to L / 268. The development of entropy (and therefore irreversibility) is therefore reduced. In the above digital example, 30.6LJK1 is obtained with the equivalent heat pump circuit according to the invention, against 33.3L JK 1 with the known arrangement. An improvement of about li% is therefore obtained.

In addition, to cool the working fluid to the inlet temperature in the evaporator, the mass of the working fluid which must be vaporized to reduce the cooling required is Cp. t T, where Cp is the specific heat
The form, at constant pressure, of the working fluid and AT is the temperature drop experienced when the two-phase mixture passes from the throttling element to the inlet of the evaporator.

In the known arrangement using an isobaric evaporator, AT is 300K whereas with the invention, AT is 15 K. The loss of capacity is therefore halved in the second case. It should be noted that the approximate value of Cp.QT in the numerical example above is 0.1 times the total capacity of a conventional working fluid, wherellT = 15 "R.

 The reduction in capacity is therefore of the order of 10%.

 To progressively relax the two-phase mixture from the throttle, with a distributed temperature reduction and absorption of the heat from the heat source, the atomization device can be equipped with heat transmission means intended to transmit heat from a two-phase mixture heat source passing through the evaporator. In a simplified arrangement, the heat transmission means can be part of the atomization device proper. For example, the heat transmission means may be a heat conducting part, placed in heat communication between an external source of heat, such as the ambient atmosphere, and the two-phase mixture located in the atomization device. .

 The atomization device advantageously comprises means intended to cause the flow of the two-phase mixture in order to divide and recombine it repeatedly before it leaves the atomization device. An advantageous method making it possible to obtain this result consists in equipping the atomization device with a tube having a substantially cylindrical lumen and an inlet and an outlet respectively at its two ends, a core being housed in the tube, roughly coaxially with, but at a distance from the wall of the light, the peripheral surface of the core having at least one non-intersecting helical groove which extends continuously around the core, substantially over its entire length, and means establishing a path helical between the core and the wall of the tube to define at least one helical path extending continuously around the core in communication with the helical groove or grooves, but not opposite them. The points where the or each helical groove intersects the or each helical path serve to divide and recombine the flow of the two-phase mixture through the atomizing device. It should be noted that this crossing of the respective flow paths, produced by the helical groove (s) and the helical path (s), generates a two-phase interaction and shearing of the mixture, leading to an intimate mixing and the splitting of the liquid droplets into a fine mist, which favors the production of vapor phase flowing from the output of the atomization device.

 The means forming helical paths can be fixed to the peripheral surface of the core and can be in frictional contact with the wall of the tube so that the core and the means forming the helical paths form an assembly which is detachably fixed. in the tube by said friction contact and which can be removed in one piece from the tube. The core is usually cylindrical and has at least one helical groove extending inward from its cylindrical surface.

 In another preferred form of arrangement, the core is an elongated element of rectangular section, advantageously square, which is twisted along its length, around its longitudinal axis, so that four helical grooves are formed in the peripheral surface of this core , the tube also being of rectangular section, for example square, and being twisted in the opposite direction to that of the core.

 To improve the efficiency of the heat pump circuit, this circuit may also include heat exchange means intended to exchange heat between the working fluid supplied to the atomization device and that which comes therefrom.

The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting examples and in which
Figure 1 is a schematic representation of a known heat pump circuit using an isobaric evaporator
Figure 2 is a schematic view of a preferred form of the invention
Figure 3 is a section along line AA of Figure 2
Figure 4 is a view similar to that of Figure 3, but showing a variant
FIG. 5 is a Mollier diagram (enthalpieentropia) illustrating the improvement that can be obtained during the implementation of the invention
Figure 6 is a very schematic illustration of another advantageous arrangement of the evaporator in the heat pump circuit according to the invention;
Figure 7 is a very schematic view of an advantageous and practical design for the evaporator; and
FIG. 8 is a diagram of a two-stage heat pump circuit constituting another advantageous embodiment of the invention.

 Figure 1 shows a typical circuit which is known from a vapor compression heat pump. As shown, the heat from a source 1 is circulated in a heat exchange coil 2 immersed in a working liquid contained in a closed container 3, from an evaporator 12, and heat is transmitted from the coil 2 to the working liquid. A space 22 filled with steam exists in the container 3 above the working liquid and saturated steam, coming from this space, circulates by a conduit 4 towards a compressor 5 where it is compressed for give superheated steam which is transported by a pipe 6 (with a certain pressure drop and a certain cooling) to a condenser 7 which extracts heat from superheated steam (isothermal condensation) to circulate it towards a user load 8 in order to produce a saturated liquid which is directed towards a throttle (for example a needle valve) or a shutter element 10. The saturated liquid is expanded through the shutter or throttle element 10 In order to form a two-phase liquid / vapor mixture which is introduced via a line 9 into the working liquid contained in the container 3 of the evaporator 12. For this purpose, the line 9 descends inside the container 3 and ends up a short distance above the bottom of this closed container 3. The gas phase of the two-phase mixture introduced into the container forms bubbles which rise up through the working liquid of container 3 and pass into the space 22, filled with saturated steam, from the evaporator. The thermal efficiency of the heat pump circuit can be improved by the use of a heat exchanger 11 performing a heat exchange between the saturated working liquid s' flowing from the outlet of the condenser 7 to the throttling element 10 and the saturated steam circulating in the duct 4.

 As mentioned in the preamble to this memo, the main causes of the irreversibility of the heat pump circuit of FIG. 1 are the relaxation occurring in the throttling element 10, since this relaxation produces no work. recoverable, and the isobaric, and therefore isothermal, heat exchange takes place in the condenser and in the evaporator. The embodiment of the invention, illustrated in Figures 2 and 3, is improved with respect to this point. The same reference numerals used in FIG. 1 and in FIGS. 2 and 3 designate the same elements or equivalent elements which will not be described again in detail below.

 In the heat pump circuit of FIGS. 2 and 3, the difference, compared to the previous circuit, lies in the expansion of the saturated liquid transported to the throttling element 10 and the evaporator 12 to form saturated vapor which is directed to the compressor 5. First, the isenthalpic pressure drop occurring through the throttle member 10 is considerably less than that occurring with the throttle member of the embodiment of Figure 1 In fact, the sole purpose of the throttling or sealing element is to ensure that the section of the conduit 9 located upstream of this throttling element 10 contains saturated liquid, and the degree of throttling must This saturated liquid is expanded in the throttle element 10 to form a two-phase mixture which is then further expanded in the evaporator 12 which includes a device 13 for atomization as well as a coil 2 of heat exchange related to the heat source 1 which is in thermal communication with the two-phase mixture of the working fluid expanding in the atomization device 13.

 As shown in FIGS. 2 and 3, the atomizing device 13 comprises a core 21 represented in the form of a core or of a cylindrical core, although other elongated shapes are possible, the cylindrical surface of which has two twisted, wide and deep grooves or grooves 15, extending inwards, each rotating in a helix around the core substantially over its entire length, and advantageously forming more than three complete turns (although, only for reasons of simplicity, two complete turns are shown in figure 2). The actual number of revolutions must, in principle, be determined experimentally, or calculated, depending on the cross-sectional area and the mass flow rate of the evaporating fluid. The shape of the core 21 is similar to that of a metal drill bit. For example, for a core diameter of 4 mm, its length must be at least 80 mm.

 Two metal wires 16, each having, in section, a diameter of 1 mm, for example, are wound around the core. As before, the wires are wound in a helix but the turns of these helices are in the opposite direction to that of the turns of the helical grooves 15 of the core 21. Each wire 16 forms, as before, three complete turns over a length of 80 mm and is fixed to the core 21, for example by a few solder points. The core assembly thus formed is inserted axially inside a cylindrical tube 17, the lumen diameter of which is 6 mm, and is adjusted by force or by tight friction. The tube is closed at each end by a cap 18 having a central hole 19 in axial alignment with the core 21 and with which the conduit 9 or 4, as the case may be, is fluid-tightly connected by any suitable means of connection. it is obvious that at least one of the end caps 18 must be removably attached to the tube 17 of the atomization device 13 to allow the assembly of this device during manufacture and any subsequent disassembly desired and any refitting place of the core assembly, but this is not illustrated in FIG. 2 for clarity. it is obvious that the values indicated for the numbers of grooves 15 and 16 as well as for the number of turns of each of them, over the length of the atomization device, as well as the dimensions given, are only indicated as an example.

FIG. 2 very schematically illustrates the coil 2 for heat exchange in thermal communication with the two-phase mixture circulating through the atomization device. For example, the coil 2 can be wound in a helix around the outer surface of the cylindrical tube 17 which is obviously made of a material with high thermal conductivity, for example metal. Alternatively, the outer surface of the cylindrical tube 17 can be simply exposed to the ambient atmosphere so that the evaporator 12 takes off
Its heat from the surrounding medium to evaporate the two-phase mixture.

 During the operation of the heat pump circuit, the two-phase mixture coming from the throttling element 10 circulates in the conduit 9 and arrives at the inlet end of the atomization device 13 where it meets the paths helical flow, of opposite pitches, formed respectively by the helical grooves or channels 15 and the wires 16 wound in a helix. The effect of these flow paths of opposite steps is to quickly divide and recombine the two-phase mixture, at the points of intersection between the flow paths of opposite steps. phases progresses through the atomization device 13, we see that it extracts heat from the source 1 and that at the same time, an atomization and a vaporization occur, with reduction of temperature, because the mixture with two phases cools to promote its own vaporization. In this way, the mixture of two phases arriving at the inlet end of the atomization device 13 is transformed, with pressure reduction and temperature reduction, into the pure vapor phase flowing from the outlet end of the atomizing device 13, at a high speed. it should be noted that the stirring, shearing, swirling and mixing caused by the core assembly of the atomizing device ensures that the liquid phase of the two-phase mixture is both finely divided in whole, and mixed intimately in the vapor phase.

 it should be noted that the numerical example given in the preamble of this memo can be applied to the known heat pump circuit, shown in Figure 1, and to the embodiment of Figures 2 and 3, respectively, as comparison intended to illustrate the improvement, which can be obtained with the embodiment of FIGS. 2 and 3, by reducing the degree of expansion in the throttling element and eliminating the isobaric and isothermal evaporation of the working fluid.

 The improvement is further illustrated in FIG. 5 which shows the operating cycle of the working fluid on an enthalpy-entropy diagram of Mollier. In this figure, a classic saturated vapor curve for the working fluid is indicated in 100 and its saturated liquid curve is given in 13L The cycle AB-B'-C-C'-DE-E'-A represents the cycle of the working fluid of the known heat pump circuit, shown in FIG. 1 (with the heat exchanger II present). Point A represents the output of the two-phase mixture from the throttle element 10. Line A-B represents the isothermal expansion of the two-phase mixture in the evaporator 12 to form saturated vapor (point B) which is superheated by exchange with the liquid in the evaporator.

This isobaric heating is indicated in B-B '. Line BC represents a polytropic compression, in compressor 5, of superheated steam whose pressure and temperature, upstream of the condenser, drop (C-C'-D), followed by isothermal condensation in condenser 7 ( line DE), cooling (E-E ') by heat exchange with the vapor coming from the evaporator (E-E'), and finally isenthalpic expansion through the throttling element 10 ( line
E'-A).

In the heat pump circuit of Figures 2 and 3, the throttling element 10 and the evaporator 12 cooperate so as to modify the part E'-ABB 'of the cycle in a path
E'-FBB 'shown in Figure 5. Thus, as mentioned above, the degree of relaxation in the throttling element 10 is very reduced, which brings the point F much closer to the point E' of the curve 101 saturated liquid as point A. The expansion and evaporation in the evaporator 12 then follow the line FB-B '. It will be noted that the area FAB represents the reduction in irreversibility which can be obtained with the embodiment of FIGS. 2 and 3.

 In a variant (see FIG. 4) of the embodiment of FIGS. 2 and 3, instead of using metal wires surrounding a core with helical grooves, a bar 14 of rectangular section, advantageously square, which can be twisted, is used along its length, around its longitudinal axis, so as to form four helical grooves 15, and this twisted bar is adjusted inside a tube 17 of rectangular section, advantageously square, which is twisted along its length, in opposite direction to that of bar 14, in the same manner as in FIGS. 2 and 3.

 it should be noted that the expansion of the working fluid in the atomizing device 13 produces work, namely in the form of an acceleration of the working fluid, which is used to overcome the pressure losses of the evaporator. it should be noted that this work is free, as it comes from the increased development of entropy in the course of evaporation. The pressure drop due to the evaporator therefore does not require additional work on the part of the compressor. it may even be that the speed of the vapor at the outlet end of the evaporator 12 can be recovered under pressure and therefore completes the work produced by the compressor. This can be obtained by a suitable aerodynamic design of the outlet of the evaporator and the inlet of the compressor connected together. This speed recovery is indicated in B'-B "in FIG. 5.

EXAMPLE
We will now give an example of the design of a 10 kW evaporator where the working fluid is halogen R22 (monochlorodifluoromethane) having the following properties
Latent heat: 190 kJ.kg-l
Molar mass: 90
Evaporation temperature: 100C
Average evaporation pressure (p): 7 bars
Specific volume (V): 0.0338 m3.kg 1
pV: 23700 Pa.m3.kg 1
Speed of sound: 180 ms -1
Mass flow for 10 kW: 52 gs -1
If the speed of the halogenated fluid is limited to mach 0.6 (100m.s -1), the area of the flow section is 33.8. 52 / 10,000 = 0.176 cm2, which is obtained with an 8.4 mm diameter core, inserted into a 12 mm inner diameter tube. In fact, a mixer was constructed with an 8mm core, 2mm metal wire as a spacer, and a 12mm inner diameter tube. The outside diameter of this tube is 14 mm, its perimeter is therefore 44 mm, and the length necessary to obtain an exchange surface of 1 m2 must therefore be 23 m. This tube, suitably equipped with fins to increase the heat exchange area, can have an exchange surface 3 or 4 times larger, so that its length can be reduced to 6 m. To improve relaxation and mixing, this tube is preceded by a 4 mm core mixer, having a cross-section
internal flow of 4 mm2 (4.5 mm2 minus the remaining tube
exchanger), so it is reasonable to limit it to
a few percent (10 to 15) evaporation occurs
in this tube. Since some of the liquid
evaporates by itself upstream of the entry of this tube, the area
external heat exchange of this tube is limited to 8 - -
of the total heat exchange area presented by the successive tubes. The outer perimeter of this first tube is 25 mm, and this tube, suitably equipped with fins, has an area of 750 cm2 per meter.

 In a first approximation, this evaporator (see FIG. 6) includes a serpentine tube arrangement comprising a single inlet mixer section 50 of 1 meter in length, with a 4 mm core, followed by six successive mixer sections 51 one meter long, with a core of 8 mm. The halogen inlet pipe in the inlet mixer section is indicated at 52 and the outlet pipe of the serpentine tube, leading to the compressor 5, is designated by the reference 53. The cooling fins carried by the sections 51 of the mixer are shown at 54 and each of the mixer sections 50, 51 is placed in a water tube 55 surrounding it, the tubes 55 being connected together in series. and connected in a circuit to be supplied by the heat source 1.

 The pressure drop of the halogen in the evaporator is then evaluated or measured on a prototype and the calculations are continued until all the parameters (temperatures, pressures, heat and mass flow rates) correspond, in sequence of empirical processes, to the criteria provided which, in an arrangement, are that the pressure drop of the halogen through the evaporator 12 is 2 bars, that the halogen evaporates by itself, before entering the inlet of the evaporator, at 150C (7.8 bars) and that it leaves the evaporator at 50C (5.8 bars), and the inlet and outlet temperatures of the water are 200C and 100C, respectively.

 In another practical arrangement (FIG. 7) for the evaporator 12, in which the pressure drop of the working fluid (for example a halogenated fluid) is kept at a low value, the evaporator 12 comprises a series of sections 30 d evaporator whose cross-sectional area increases for the flow of halogen. The successive sections are arranged in a water jacket 31. The number of sections and the overall length (which define the area of the heat exchange surface) are determined according to the criteria required for passage through the evaporator .

 A two-stage heat pump circuit is illustrated in FIG. 8. In this embodiment, the working fluid is expanded through a throttling element 10 and an atomizing device 13 (similar in construction to that of the atomization device 13 in FIGS. 2 and 3) up to an intermediate pressure, in an instant vaporization chamber 23, and the vapor released in the vapor space of the instant vaporization chamber is then directed towards the inlet of the second stage compressor 5. The liquid in the bottom of the instantaneous vaporization chamber is expanded through a second throttling element 24 and is directed to the evaporator 12 in the conventional manner. The vaporized working fluid coming from the evaporator 12 is then compressed by a compressor 25 of the first stage and it is introduced into the inlet of the atomization device 13 where it combines and mixes with the fluid coming from the throttle 10 The atomization device 13 here improves the efficiency of the instantaneous vaporization chamber 23 compared to that which it would have in the absence of this atomization device.

 British patent No. 1,553,875 describes in more detail the construction and operation of the atomization device shown in FIGS. 2 to 4.

 It goes without saying that many modifications can be made to the heat pump circuit described and shown without departing from the scope of the invention.

Claims (12)

 1. Steam compression heat pump circuit, characterized in that it has a throttle (10) through which a working liquid from the condenser <7) of the heat pump circuit expands, this throttle being designed to deliver a two-phase liquid / vapor mixture and being followed by an atomizing device (13) which is designed to gradually relax the two-phase mixture from the throttle, with a distributed reduction in temperature, in order to produce saturated steam intended to be compressed by the compressor (5) of the heat pump circuit.  2. Heat pump circuit according to claim 1, characterized in that the atomization device comprises means (2) for transmitting heat intended to transmit heat from a source (1) to the two-phase mixture passing through. the circuit evaporator (12).  3. Steam compression heat pump circuit, characterized in that it comprises a throttle (10) through which the saturated liquid is expanded to form a liquid with two liquid / vapor phases, an evaporator (12) intended to gradually relax the two-phase mixture coming from the throttle, with a distributed reduction in temperature, to produce saturated steam, a compressor (5) intended to compress the saturated steam to produce superheated steam, and a condenser ( 7) intended to extract heat, to transmit it to a user load (8), steam coming from the compressor in order to produce the saturated liquid intended for throttling.  4. Heat pump circuit according to claim 3, characterized in that the evaporator comprises an atomization device (13) intended to atomize the liquid phase of the two-phase mixture and means (2) for transmitting heat intended transmitting heat from a source (1) to the two-phase mixture passing through the evaporator.  5. Heat pump circuit according to any one of claims 1, 2 and 4, characterized in that the atomization device comprises means intended to induce the flow of the two-phase mixture in order to divide and recombine it. repeatedly before it leaves the atomizing device.  6. Heat pump circuit according to claim 5, characterized in that the atomization device comprises a tube (17) which has a substantially cylindrical lumen having an inlet and an outlet located respectively at its two ends, a core (21 ) housed in the tube, substantially coaxial with the wall of the lumen, but spaced from this wall, the peripheral surface of the core having at least one non-intersecting helical groove (15) which extends continuously around the core , substantially over its entire length, and means (16) for forming helical paths being arranged between the core and the wall of the tube and defining at least one helical path which extends continuously around the core, in communication with the groove or the heli-cold grooves, but not opposite to that of this groove or these grooves.  7. Heat pump circuit according to claim 6, characterized in that the means forming helical paths are fixed to the peripheral surface of the core and are in frictional contact with the wall of the tube so that the core and the means forming the helical paths constitute a core assembly which is fixed in a removable manner in the tube, by said friction contact, and which can be removed in one piece from the tube.  8. Heat pump circuit according to one of claims 6 and 7, characterized in that the core is substantially cylindrical and has at least one helical groove extending towards the inside of its cylindrical surface.  9. Heat pump circuit according to one of claims 6 and 7, characterized in that the core is an elongated element (14) of rectangular section which is twisted along its length, around its longitudinal axis, in order to form four helical grooves (15) in the peripheral surface of said core, the tube (17) being of rectangular section.  10. Heat pump circuit according to claim 9, characterized in that the elongate element and the tube both have a square section.  11. Heat pump circuit according to any one of the preceding claims, characterized in that it further comprises a heat exchanger (11) intended to carry out a heat exchange between the working fluid supplied to the atomization device. and the one coming out.  12. Method for supplying heat to a user load using a vapor compression heat pump circuit, characterized in that it consists in expanding a working liquid through a constriction to form a mixture two-phase liquid / vapor, gradually expanding the two-phase mixture, with a distributed reduction in temperature and absorption of heat from a source to produce saturated vapor, compressing the saturated vapor to produce superheated steam, to extract the heat, intended for a load, from a part of the circuit between the compressor and the throttle, and to repeat these operations.