Refrigerant circuit

Abstract

The invention relates to a refrigerant circuit (10, 110) comprising an evaporator (12), a compressor (14) with a variable volume, a refrigerant (20), which is in a liquid and / or gaseous state and is received in the evaporator (12) and in the compressor (14), a supply line (16), which leads from the evaporator (12) to the compressor (14), for supplying the refrigerant (20) from the evaporator (12) to the compressor (14), and a return line (18), which leads from the compressor (14) to the evaporator (12), for returning the refrigerant (20) from the compressor (14) to the evaporator (12). According to the invention, the compressor (14) contains a liquid auxiliary medium (32) in which the refrigerant (20) is insoluble or sparingly soluble and which is in contact with the refrigerant (20).

Description

[0001] Refrigerant circuit

[0002] The invention relates to a refrigerant circuit according to the preamble of claim 1.

[0003] Such refrigerant cycles are already widely used, for example in heat pumps. In this process, the liquid refrigerant is evaporated by absorbing ambient heat, compressed by the compressor, and condensed under pressure, releasing usable heat. Once back in its liquid state, the refrigerant is returned to the evaporator, allowing the process to begin again. A general problem with heat pumps, and also with other applications of refrigerant cycles of the type mentioned above, is that the achieved efficiency, or the ratio of usable heat output to mechanical drive power, is often unsatisfactory.

[0004] It is therefore an object of the invention to further develop a refrigerant circuit of the type mentioned above in such a way that it enables a better efficiency.

[0005] This problem is solved according to the invention by a refrigerant circuit having the features of claim 1. Advantageous embodiments of the invention are the subject of the dependent claims.

[0006] The invention is based on the idea of ​​providing an additional heat transfer medium, a liquid auxiliary medium, to improve heat exchange. The auxiliary medium always retains its liquid state, while the refrigerant cyclically evaporates and condenses during operation of the refrigerant circuit. Furthermore, the auxiliary medium enables compression that is at least largely free of voids. Due to its liquid state, the auxiliary medium is essentially incompressible in the sense that its compression modulus is greater than 0.5 GPa. To prevent excessive and potentially irreversible or difficult-to-reverse mixing of the refrigerant and the auxiliary medium, the refrigerant is insoluble or only slightly soluble in the auxiliary medium, meaning that its solubility in the auxiliary medium is less than 0.1 mol / l and preferably less than 0.01 mol / l.It is preferred that the auxiliary medium be water, which is nearly incompressible and has a high specific heat capacity. An alkane, in particular butane or propane, is preferred as the refrigerant, wherein the solubility of butane in water is approximately 0.0011 mol / l and the solubility of propane in water is approximately 0.0017 mol / l, both at 20°C. It is further preferred that the refrigerant, even in its liquid state, has a lower density than the auxiliary medium. It is then arranged above the auxiliary medium in the compressor.

[0007] Preferably, the auxiliary medium, expediently in a constant quantity, is also contained in the evaporator and flows through it with the refrigerant as it passes from the return line to the supply line. The presence of the auxiliary medium as a heat transfer medium in the evaporator also enables better heat transfer there. In particular, if the refrigerant has a lower density than the auxiliary medium, even in its liquid state, the return line advantageously terminates at a lower end of the evaporator, and the supply line expediently branches off from an upper end of the evaporator.

[0008] Advantageously, a compensating line branches off from the return line to an expansion tank to compensate for volume changes of the refrigerant. It is preferred that a first valve and a second valve, located closer to the evaporator and at a distance from the first valve, are provided for shutting off the return line. The compensating line advantageously branches off from the return line between the first and second valves. Furthermore, a second valve is preferably provided for shutting off the supply line. The process of cyclical evaporation and condensation of the refrigerant can be controlled by appropriately actuating the valves.

[0009] Advantageously, a heat exchanger is provided through which the supply line and / or the return line runs, enabling internal heat exchange. A section of the return line can be arranged around a section of the supply line, or vice versa, with this circumferential arrangement preferably taking place within the heat exchanger. In this way, the gaseous refrigerant is preheated before being supplied to the compressor. This preheating is more efficient if the refrigerant flows in the opposite direction in the return line to that in the supply line, following a counterflow principle.

[0010] Advantageously, the volume of the compressor can be varied, for example, by means of a piston that is movable within the compressor. It is preferred that the compressor contains a constant quantity of the auxiliary medium, which is in contact with the piston. In this way, the refrigerant in the compressor can be compressed or expanded due to the movement of the piston, with the auxiliary medium acting as a liquid piston. However, it is also possible for the volume of the compressor to be varied by adding or removing auxiliary medium, particularly by means of a pump.

[0011] The refrigerant cycle according to the invention can be operated, in particular, as a heat pump. In a first step, the volume of the compressor is increased, whereby liquid refrigerant evaporates by absorbing heat from the auxiliary medium. In a second step, the volume of the compressor is reduced by increasing the pressure in the refrigerant and releasing heat into the auxiliary medium. In a third step, the volume in the compressor is further reduced, and gaseous refrigerant is condensed in the compressor, releasing heat to the auxiliary medium. Thus, in the second step, a preferably at least approximately isothermal compression takes place, and in the third step, an isothermal condensation of the refrigerant occurs. Finally, in a fourth step, condensed refrigerant is expelled from the compressor by further reducing its volume, and the sequence of four steps is repeated several times.

[0012] It is preferred that during the first step the first valve is closed, while the second valve and the subsequent valve are open. It is further preferred that during the second step and during the third step the first valve, the second valve, and the subsequent valve are closed.

[0013] Finally, it is preferred that during the fourth step the first valve is open, while the second valve and the subsequent valve are closed.

[0014] Advantageously, after preheating by passing the refrigerant through the heat exchanger, it is isothermally compressed by internal heat exchange, whereby useful heat is removed from the refrigerant.

[0015] The invention will now be explained with reference to two exemplary embodiments illustrated in the drawing. The drawing shows...

[0016] Figs. 1a to d show a schematic representation of a refrigerant circuit according to a first embodiment during a first, a second, a third and a fourth process step when operating as a heat pump and

[0017] Fig. 2 shows a schematic representation of a refrigerant circuit according to a second embodiment during the second process step when operating the refrigerant circuit as a heat pump.

[0018] The refrigerant circuit 10 according to the first embodiment (Figs. 1a to d) comprises an evaporator 12 and a compressor 14. A supply line 16 leads from the evaporator 12 to the compressor 14, and a return line 18 leads from the compressor 14 to the evaporator 12. A refrigerant 20 is contained in the evaporator 12, the compressor 14, the supply line 16, and the return line 18, the state of which changes between liquid and gaseous during the process steps shown in Figs. 1a to d. In the present embodiment, the refrigerant 20 is an alkane, namely butane or propane. A first valve 22 is arranged at the outlet of the compressor 14 for closing and opening the return line 18, while a second valve 24 is arranged at the inlet of the evaporator 12 for closing and opening the return line 18. At the entrance to the compressor 14, there is also another valve 26 for shutting off and releasing the supply line 16.Between the first valve 22 and the second valve 24, a compensating line 28 branches off from the return line 18, which leads into a compensating reservoir 30.

[0019] The compressor 14 also contains an auxiliary medium that is liquid and essentially incompressible, and in which the refrigerant 20 is insoluble or only sparingly soluble. In the present embodiment, the auxiliary medium 32 is water. The volume of the compressor 14 is variable by virtue of a connecting line 34 and a cylinder 36 in which a piston 38 is movable back and forth. The refrigerant 20 is always located above the surface of the auxiliary medium 32, or above its level, within the compressor 14. Since, in the embodiment shown here, the refrigerant 20 has a lower density than the auxiliary medium 32, even in its liquid state, and is also insoluble or only sparingly soluble in it, the auxiliary medium 32 acts like a liquid piston when the piston 38 moves within the cylinder 36. This piston pressurizes the refrigerant 20 in the compressor 14, allowing it to be expelled without creating a void.The auxiliary medium 32 is also contained in the evaporator 12, but does not completely fill its volume. Therefore, the surface of the auxiliary medium 32 in the evaporator 12 is located below its upper end 40, from which the supply line 16 branches off. The return line 18, on the other hand, branches off from the upper end 42 of the compressor 14 and opens into the lower end 44 of the evaporator 12. During the first process step shown in Fig. 1a, when operating the refrigerant circuit as a heat pump, the first valve 22 is closed, while the second valve 24 and the further valve 26 are open. During the first process step, the volume of the compressor 14 is increased by retracting the piston 38 in the cylinder 36, causing liquid refrigerant 20 to evaporate and fill the increasing volume in the compressor 14. The evaporation of the refrigerant 20 occurs, among other things, through the absorption of heat from the auxiliary medium 32.Once the piston 38 is retracted, the second valve 24 and the further valve 26 are also closed. In a second process step (Fig. 1b), the volume of the compressor 14 is reduced by increasing the pressure in the refrigerant 20, as the piston 38 is pushed forward again, causing the level of the auxiliary medium 32 in the compressor 14 to rise. In this process step, the refrigerant 20 is compressed. This compression preferably occurs at least approximately isentropically. Following the second process step, in a third process step (Fig. 1c), during which all three valves 22, 24, 26 are also closed, the volume in the compressor 14 is further reduced by advancing the piston 38 in the cylinder 36 and increasing the level of the auxiliary medium 32 in the compressor 14, whereby gaseous refrigerant 20 condenses in the compressor 14, releasing heat, among other things, to the auxiliary medium 32.In this third process step, the refrigerant 20 undergoes isothermal condensation. Subsequently, the first valve 22 is opened, while the second valve 24 and the further valve 26 remain closed. In a fourth process step (Fig. 1d), the condensed refrigerant 20 is expelled from the compressor 14 by further reducing its volume through further advancement of the piston 38 and a further increase in the level of the auxiliary medium 32 within the compressor 14. After the refrigerant 20 has been expelled from the compressor 14, the first valve 22 is closed again, and the second valve 24 and the further valve 26 are opened, allowing the first process step (Fig. 1a) to be carried out once more.The sequence of the four process steps is then repeated cyclically, whereby in the first process step liquid refrigerant 20 from the return line 18 enters the evaporator 12 and rises there in the auxiliary medium 32 without mixing with it and thereby evaporates.

[0020] The refrigerant circuit 110 according to the second embodiment differs from the refrigerant circuit 10 according to the first embodiment only by a few additional arrangements or components. Therefore, identical features are designated with the same reference numerals.

[0021] In the refrigerant circuit 110 according to the second embodiment, the connecting line 34 is omitted. Furthermore, a heat exchanger 50 is provided, through which a section 52 of the supply line 16 runs centrally, and which is in turn filled with water. The section 52 of the supply line 16, which is arranged in the heat exchanger 50, is also filled with the auxiliary medium 32 and can thus also be considered an extension of the evaporator 12. A section 54 of the return line 18 is arranged around the section 52 of the supply line 16, which is arranged in the heat exchanger 50. The flow directions of the refrigerant 20 in section 52 of the supply line 16 and in section 54 of the return line 18 are opposite to each other, so that condensed warm refrigerant 20 in section 54 of the return line 18 flows in the opposite direction to the evaporated refrigerant 20 rising in section 52 of the supply line 16 and releases heat to it.By appropriately controlling the valves 22, 24, 26 and moving the piston 38, the refrigerant circuit 110 according to the second embodiment carries out the four process steps described above in the same sequence as the refrigerant circuit 10 according to the first embodiment, wherein in the second process step a preferably isothermal compression of the refrigerant 20 takes place.

[0022] In summary, the following can be stated: The invention relates to a refrigerant circuit 10, 110 with an evaporator 12, with a compressor 14 having a variable volume and at least largely free of void space, with a refrigerant 20 in liquid and / or gaseous state contained in the evaporator 12 and in the compressor 14, with a supply line 16 leading from the evaporator 12 to the compressor 14 for supplying the refrigerant 20 from the evaporator 12 to the compressor 14, and with a return line 18 leading from the compressor 14 to the evaporator 12 for returning the refrigerant 20 from the compressor 14 to the evaporator 12. According to the invention, it is provided that the compressor 14 contains a liquid auxiliary medium 32 in which the refrigerant 20 is insoluble or only sparingly soluble, and which is in contact with the refrigerant 20.

Claims

Claims 1. Refrigerant circuit with an evaporator (12), with a compressor (14) having a variable volume, with a refrigerant (20) in liquid and / or gaseous state contained in the evaporator (12) and in the compressor (14), with a supply line (16) leading from the evaporator (12) to the compressor (14) for supplying the refrigerant (20) from the evaporator (12) to the compressor (14) and with a return line (18) leading from the compressor (14) to the evaporator (12) for returning the refrigerant (20) from the compressor (14) to the evaporator (12), characterized in that a liquid auxiliary medium (32) is contained in the compressor (14) in which the refrigerant (20) is insoluble or only sparingly soluble and which is in contact with the refrigerant (20).

2. Refrigerant circuit according to claim 1, characterized in that the auxiliary medium (32) is water.

3. Refrigerant circuit according to claim 1 or 2, characterized in that the refrigerant (20) is an alkane, in particular butane or propane.

4. Refrigerant circuit according to one of the preceding claims, characterized in that the auxiliary medium (32) is contained in the evaporator (12) and is passed through by the refrigerant (20) when it flows from the return line (18) to the supply line (16).

5. Refrigerant circuit according to one of the preceding claims, characterized in that an expansion line (28) branches off from the return line (18) to an expansion tank (30).

6. Refrigerant circuit according to one of the preceding claims, characterized by a first valve (22) and a second valve (24) arranged at a distance from the first valve (22) closer to the evaporator (12) for shutting off the return line (18).

7. Refrigerant circuit according to claim 5 and claim 6, characterized in that the compensating line (28) branches off from the return line (18) between the first and the second valve (23, 24).

8. Refrigerant circuit according to one of the preceding claims, characterized by a further valve (26) for shutting off the supply line (16).

9. Refrigerant circuit according to one of the preceding claims, characterized by a heat exchanger (50) through which the supply line (16) and / or the return line (18) runs.

10. Refrigerant circuit according to one of the preceding claims, characterized in that a section (52) of the return line (18) is arranged circumferentially around a section (54) of the supply line (16) or that a section of the supply line (16) is arranged circumferentially around a section of the return line (18), preferably in the heat exchanger (50).

11. Refrigerant circuit according to claim 10, characterized in that the refrigerant (20) flows in the section (52) of the return line (18) in the opposite direction to that in which it flows in the section (54) of the supply line (16).

12. Refrigerant circuit according to one of the preceding claims, characterized in that the volume of the compressor (14) is variable.

13. Refrigerant circuit according to claim 12, characterized in that the volume of the compressor (14) is variable by means of a movable piston (40).

14. Refrigerant circuit according to claim 12 or 13, characterized in that the compressor (14) contains a constant quantity of the auxiliary medium (32) which is in contact with the piston (40).

15. Refrigerant circuit according to claim 12, characterized in that the volume of the compressor (14) is variable by adding or removing auxiliary medium (32).

16. A method for operating a refrigerant circuit (10, 110) according to one of the preceding claims as a heat pump, wherein in a first step the volume of the compressor (14) is increased, wherein liquid refrigerant (20) evaporates by absorbing heat from the auxiliary medium (32), wherein in a second step the volume of the compressor (14) is decreased by increasing the pressure and releasing heat to the auxiliary medium (32), wherein in a third step the volume in the compressor (14) is further decreased and gaseous refrigerant (20) condenses in the compressor (14) releasing heat to the auxiliary medium (32), wherein in a fourth step condensed refrigerant (20) is expelled from the compressor (14) by further decreasing its volume, and wherein the sequence of the four steps is repeated several times.

17. Method according to claim 16 using a refrigerant circuit (10, 110) according to claim 7 and claim 8, characterized in that during the first step the first valve (22) is closed while the second valve (24) and the further valve (26) are open.

18. Method according to claim 17, characterized in that during the second step and during the third step the first valve (22), the second valve (24) and the further valve (26) are closed.

19. Method according to claim 17 or 18, characterized in that during the fourth step the first valve (22) is open, while the second valve (24) and the further valve (26) are closed.

20. Method according to one of claims 16 to 19 using a refrigerant circuit (110) according to claim 9, characterized in that after preheating the refrigerant (20) by passing it through the heat exchanger (50) the refrigerant (20) is isothermally compressed with the removal of useful heat.

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