REFRIGERANT

Abstract

The invention relates to a refrigerant for a cooling device (10) comprising a cooling circuit (11) comprising at least one heat exchanger (12), the refrigerant undergoing a phase transition in the heat exchanger, the refrigerant being a refrigerant mixture composed of a fraction of carbon dioxide (CO.sub.2), a fraction of 1,1-difluoroethene and a fraction of at least one other component, wherein the fraction of carbon dioxide in the refrigerant mixture is 45 to 90 mole percent, the fraction of 1,1-difluoroethene being 5 to 40 mole percent.

Claims

1. A refrigerant for a cooling device (10, 23, 30, 36, 39, 44, 49, 55, 60) having a cooling circuit (11, 24, 42, 50) comprising at least one heat exchanger (12, 25, 48, 54) in which the refrigerant undergoes a phase transition, the refrigerant being a refrigerant mixture composed of a fraction of carbon dioxide (CO.sub.2), a fraction of 1,1-difluoroethene (C.sub.2H.sub.2F.sub.2), and a fraction of at least one other component, wherein the fraction of carbon dioxide in the refrigerant mixture is 45 to 90 mole percent, the fraction of 1,1-difluoroethene being 5 to 40 mole percent.

2. The refrigerant according to claim 1, wherein a fraction of carbon dioxide in the refrigerant mixture is 50 to 80 mole percent, and a fraction of 1,1-difluoroethene is 10 to 35 mole percent.

3. The refrigerant according to claim 1, wherein the other component is hexafluoroethane (C.sub.2F.sub.6), difluoromethane (CH.sub.2F.sub.2), pentafluoroethane (C.sub.2HF.sub.5) and/or fluoroform (CHF.sub.3).

4. The refrigerant according to claim 1, wherein a fraction of carbon dioxide in the refrigerant mixture is 45 to 75 mole percent.

5. The refrigerant according to claim 4, wherein a fraction of 1,1-difluoroethene is 5 to 40 mole percent.

6. The refrigerant according to claim 4, wherein another component is fluoroform (CHF.sub.3) or hexafluoroethane (C.sub.2F.sub.6), this fraction being 1 to 30 mole percent.

7. The refrigerant according to claim 4, wherein a fraction of 1,1-difluoroethene is 1 to 30 mole percent, difluoromethane (CH.sub.2F.sub.2) and pentafluoroethane (C.sub.2HF.sub.5) being other components, and a fraction of difluoromethane being 1 to 30 mole percent, and a fraction of pentafluoroethane being 1 to 30 mole percent.

8. The refrigerant according to claim 7, wherein another component is fluoroform (CHF.sub.3) or hexafluoroethane (C.sub.2F.sub.6), this fraction being 1 to 30 mole percent.

9. The refrigerant according to claim 5, wherein a fraction of fluoroform (CHF.sub.3) is 1 to 30 mole percent.

10. The refrigerant according to claim 1, wherein a fraction of carbon dioxide in the refrigerant mixture is 55 to 85 mole percent, and a fraction of 1,1-difluoroethene is 5 to 35 mole percent.

11. The refrigerant according to claim 10, wherein difluoromethane (CH.sub.2F.sub.2) and pentafluoroethane (C.sub.2HF.sub.5) are other components, and a fraction of difluoromethane is 1 to 30 mole percent, and a fraction of pentafluoroethane is 1 to 30 mole percent.

12. The refrigerant according to claim 10, wherein another component is fluoroform (CHF.sub.3) or hexafluoroethane (C.sub.2F.sub.6), this fraction being 1 to 30 mole percent.

13. The refrigerant according to claim 1, wherein a fraction of carbon dioxide in the refrigerant mixture is 55 to 90 mole percent, and a fraction of 1,1-difluoroethene is 5 to 35 mole percent.

14. The refrigerant according to claim 13, wherein fluoroform (CHF.sub.3) and pentafluoroethane (C.sub.2HF.sub.5) are other components, and a fraction of fluoroform is 1 to 30 mole percent, and a fraction of pentafluoroethane is 1 to 30 mole percent.

15. The refrigerant according to claim 1, wherein the refrigerant mixture is composed of up to three components or of four or more components.

16. The refrigerant according to claim 1, wherein the refrigerant mixture contains fluoromethane (CH.sub.3F), ethane (C.sub.2H.sub.6), 2,3,3,3-tetrafluoropropene (C.sub.3H.sub.2F.sub.4), ethene (C.sub.2H.sub.4), fluoroethene (C.sub.2H.sub.3F), ethyne (C.sub.2H.sub.2), propane (C.sub.3H.sub.8), propene (C.sub.3H.sub.6) or fluoroethane (CH.sub.2FCH.sub.3) in an amount of up to 30 mole percent each.

17. The refrigerant according to claim 1, wherein the refrigerant has a temperature glide of ≤5 K or >5 K.

18. The refrigerant according to claim, 1 wherein the refrigerant has a relative CO2 equivalent of <2500 over 100 years or that the refrigerant is nonflammable.

19. A test chamber for conditioning air, the test chamber comprising a test space which serves to receive test material and which can be sealed against an environment and is temperature-insulated, and a temperature control device for controlling the temperature of the test space, a temperature in a temperature range of −60° C. to +180° C., being establishable within the test space by means of the temperature control device, the temperature control device having a cooling device (10, 23, 30, 36, 39, 44, 49, 55, 60) comprising a cooling circuit (11, 24, 42, 50) with a refrigerant according to claim 1, a heat exchanger (12, 25, 48, 54), a compressor (13, 26, 51), a condenser (14. 27, 41, 52) and an expansion element (15, 28, 53).

20. A method of using a refrigerant comprising a refrigerant mixture composed of a fraction of carbon dioxide (CO.sub.2) of 45 to 90 mole percent, a fraction of 1,1-difluoroethene (C.sub.2H.sub.2F.sub.2) of 5 to 40 mole percent and a fraction of at least one other component, for conditioning air in a test space of a test chamber, the test space serving to receive test material and being sealed against an environment and temperature-insulated, a cooling device (10, 23, 30, 36, 39, 44, 49, 55, 60) of a temperature control device of the test chamber, which comprises a cooling circuit (11, 24, 42, 50) with the refrigerant, a heat exchanger (12, 25, 48, 54), a compressor (13, 26, 51), a condenser (14. 27, 41, 52) and an expansion element (15, 28, 53), being used to establish a temperature in a temperature of −60° C. to +180° C.

21. The use according to claim 20, wherein the refrigerant of the high-pressure side is cooled by means of an internal heat exchanger (19, 29, 47) of the cooling circuit (11, 24, 42), connected to a high-pressure side (17) of the cooling circuit upstream of the expansion element (15, 28) and downstream of the condenser (14, 27, 41), and to a low-pressure side (18) of the cooling circuit upstream of the compressor (13, 26) and downstream of the heat exchanger (12, 25, 48), the cooling of the refrigerant of the high-pressure side being used to lower an evaporation temperature at the expansion element by means of the internal heat exchanger.

22. The use according to claim 20, wherein only part of the refrigerant is evaporated in the heat exchanger (12, 25, 48, 54).

23. The use according to claim 20, wherein the refrigerant is metered and evaporated in the heat exchanger (12, 25, 48, 54) in a clocked manner during a time interval by means of the expansion element (15, 28, 53).

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0064] Hereinafter, preferred embodiments of the invention will be explained in more detail with reference to the accompanying drawings.

[0065] FIG. 1 is a schematic illustration of a first embodiment of a cooling device;

[0066] FIG. 2 is a pressure-enthalpy diagram for a refrigerant;

[0067] FIG. 3 is a schematic illustration of a second embodiment of a cooling device;

[0068] FIG. 4 is a schematic illustration of a third embodiment of a cooling device;

[0069] FIG. 5 is a schematic illustration of a fourth embodiment of a cooling device;

[0070] FIG. 6 is a schematic illustration of a fifth embodiment of a cooling device;

[0071] FIG. 7 is a schematic illustration of a sixth embodiment of a cooling device;

[0072] FIG. 8 is a schematic illustration of a seventh embodiment of a cooling device;

[0073] FIG. 9 is a schematic illustration of an eighth embodiment of a cooling device;

[0074] FIG. 10 is a schematic illustration of a ninth embodiment of a cooling device;

[0075] FIG. 11 is a temperature-enthalpy diagram for a refrigerant;

[0076] FIG. 12 is a cycle-time diagram for an expansion element;

[0077] FIG. 13 is a temperature-surface diagram for a cooling circuit.

DETAILED DESCRIPTION

[0078] FIG. 1 shows a first embodiment of a cooling device 10 of a test chamber (not shown). Cooling device 10 comprises a cooling circuit 11 with a refrigerant, a heat exchanger 12, a compressor 13, a condenser 14 and an expansion element 15. Condenser 14 is cooled by another cooling circuit 16 in the case at hand. Heat exchanger 12 is disposed in a test space (not shown) of the test chamber. Furthermore, cooling circuit 11 has a high-pressure side 17 and a low-pressure side 18, to which an internal heat exchanger 19 is connected.

[0079] FIG. 2 shows a pressure-enthalpy diagram (log p/h diagram) for the refrigerant circulating in cooling circuit 11, the refrigerant being a zeotropic refrigerant. According to a combined view of FIGS. 1 and 2, starting from position A, the refrigerant upstream of compressor 13 is aspirated and compressed, whereby a pressure is achieved downstream of compressor 13 according to position B. The refrigerant is compressed by means of compressor 13 and is subsequently liquefied in condenser 14 according to position C. The refrigerant passes through internal heat exchanger 19 on high-pressure side 17, where it is cooled further, position C′ upstream of expansion element 15 thus being reached. By means of internal heat exchanger 19, the portion of the wet vapor area (positons E to E′) not usable in heat exchanger 12 can be used to further reduce a temperature of the refrigerant (positions C′ to C). At expansion element 15, the refrigerant is relaxed (positions C′ to D′) and partially liquefied in heat exchanger 12 (positions D′ to E). Then, the wet vapor of the refrigerant enters internal heat exchanger 19 on low-pressure side 18, where the refrigerant is re-evaporated until the dew-point temperature or the dew point of the refrigerant is reached at position E′. Hence, a first subsection 20 of an evaporation section 22 of the refrigerant runs through heat exchanger 12, a second subsection 21 of evaporation section 22 running through internal heat exchanger 19. The essential aspect is that a suction pressure of compressor 13 on low-pressure side 18 is kept constant on evaporation section 22 even if the evaporation temperature at expansion element 15 changes.

[0080] The refrigerant may be refrigerant 2, 4, 6, 8 or 9 from the Table above. These refrigerants do not contain more than three components and have a high temperature glide of >5 K, which is why internal heat exchanger 19 is necessary for safe operation and for achieving temperatures of <−55° C. As described in connection with FIG. 1, with these refrigerants, a cold capacity usable at the heat exchanger 12, i.e., at the test space (not shown), is used in heat exchanger 19 to sub-cool the liquid refrigerant upstream of expansion element 15. When refrigerants having a temperature glide of >5 K are used, this effect is particularly pronounced and an increase in performance is therefore correspondingly high. A control via an elaborate sensor system is not necessary. However, dynamic load changes, i.e., temperature changes, are possible to a limited degree only because of the inertia of cooling circuit 16 and of cooling device 10. Moreover, the refrigerant located in the test space can be evaporated by heating heat exchanger 12.

[0081] FIG. 3 shows a schematic illustration of a simplest embodiment of a cooling device 23, cooling device 23 being self-controlling. Cooling device 23 comprises a cooling circuit 24 with a heat exchanger 25, a compressor 26, a condenser 27, an expansion element 28 and an internal heat exchanger 29. Depending on a temperature at heat exchanger 25, refrigerant not fully evaporated escapes from heat exchanger 25 because the temperature at heat exchanger 25 or in a test space (not shown) is no longer high enough to cause a phase transition. In this case, refrigerant still liquid is re-evaporated in internal heat exchanger 29 because a temperature difference there has to be greater than at heat exchanger 25 at all times. Once the temperature of the liquid refrigerant upstream of expansion element 28 has been reduced by heat exchange in internal heat exchanger 29, the energy density and the temperature difference achievable with it at heat exchanger 25 increase. Cooling device 23 does not require elaborate control by way of sensors etc.

[0082] FIG. 4 shows a cooling device 30 which differs from the cooling device of FIG. 3 in that it has a first bypass 31 and a second bypass 32. A controllable second expansion element 33 is disposed in first bypass 31, first bypass 31 being configured as an additional internal cooling system 34. First bypass 31 is connected to cooling circuit 24 immediately downstream of condenser 27 upstream of internal heat exchanger 29 and downstream of heat exchanger 25 and upstream of internal heat exchanger 29. First bypass 31 thus bypasses expansion element 28 with heat exchanger 25, internal heat exchanger 29 being suppliable with evaporating refrigerant via second expansion element 33. A suction gas mass flow introduced into internal heat exchanger 29 can be cooled additionally by means of first bypass 31 in case of high suction gas temperatures, which may be caused by heat exchanger 25. In this way, evaporation of refrigerant upstream of the expansion element can be precluded. Hence, first bypass 31 can be used to react to changing load cases of cooling device 30. Second bypass 32 has a third expansion element 35 and is connected to cooling circuit 24 downstream of condenser 27 and upstream of internal heat exchanger 29 and downstream of internal heat exchanger 29 and upstream of compressor 26. This allows a suction gas mass flow upstream of compressor 26 to be reduced far enough via second bypass 32 to avoid inadmissibly high final compression temperatures.

[0083] FIG. 5 shows a cooling device 36, which differs from the cooling device of FIG. 4 in that it has another bypass 37. Other bypass 37 has another expansion element 38 and is connected to cooling circuit 24 downstream of condenser 27 and upstream of internal heat exchanger 29 and downstream of internal heat exchanger 29 and upstream of compressor 26.

[0084] First bypass 31 makes it possible to react to changing load cases. So a suction gas mass flow can be introduced into internal heat exchanger 19 and additionally cooled by reinjection via first bypass 31 in the case of high suction gas temperatures which may be caused by heat exchanger 25. Thus, it can be ensured that no evaporation can occur upstream of expansion element 28. Furthermore, a reinjection via other bypass 37 can reduce the suction gas temperature upstream of compressor 26 far enough for excessively high compression end temperatures to be avoided. This makes it possible for refrigerant having a temperature glide of >5 K to be used in cryogenic temperature applications even in the case of highly dynamic load changes.

[0085] FIG. 6 shows a cooling device 39, which differs from the cooling device of FIG. 5 in that it has another cooling circuit 40. Other cooling circuit 40 serves to cool a condenser 41 of a cooling circuit 42. Condenser 41 is realized as a cascade heat exchanger 43 in the case at hand.

[0086] FIG. 7 shows a cooling device 44 having a cooling circuit 45 and another cooling circuit 46 und, in particular, an internal heat exchanger 47 in cooling circuit 45. In the case at hand, a heat exchanger 48 is disposed in a temperature-insulated test space of a test chamber (not shown).

[0087] FIG. 8 shows a schematic illustration of a simplest embodiment of a cooling device 49 without an internal heat exchanger. A cooling circuit 50 of cooling device 49 is realized with a compressor 51, a condenser 52, an expansion element 53 and a heat exchanger 54 in a temperature-insulated test space of a test chamber (not shown).

[0088] A refrigerant circulating in cooling circuit 50 may be one of refrigerants 1, 3, 5, 7 and 9 from the Table above. These refrigerants have a temperature glide of ≤5 K, which is why no internal heat exchanger is necessary for safe operation and for achieving temperatures of <55° C. The low density of the respective refrigerant makes it necessary for compressor 51 and the piping of cooling circuit 50 to be adapted accordingly in the case of low evaporation temperatures.

[0089] FIG. 9 shows a cooling device 55, which differs from the cooling device of FIG. 8 in that a first bypass 56 having a first expansion element 57 and a second bypass 58 having a second expansion element 59 are provided. First bypass 56 and second bypass 58 can be used as described in connection with FIG. 4. So a suction temperature of compressor 51 and an evaporation pressure can be set or controlled by means of first expansion element 57 and second expansion element 59.

[0090] FIG. 10 shows a cooling device 60, which differs from the cooling device of FIG. 9 in that it has another bypass 61 comprising another expansion element 62. By means of other expansion element 62, the suction gas temperature and therefore indirectly the compression end temperature can be lowered even further.

[0091] Furthermore, an effective temperature glide of the refrigerant used can be advantageously reduced in all cooling devices based on the cooling devices shown in FIGS. 3 and 8. As can be seen from the diagram of FIG. 11, a temperature glide is not linear, mostly in refrigerants having a temperature glide of >5 K. In FIG. 11, arrow 63 marks a pipe section of a cooling circuit running through a heat exchanger in a test space. A reduction of the effective temperature glide in the heat exchanger can stabilize a test space temperature. Full evaporation is achieved by exploiting an overheating of the refrigerant in the suction line of the compressor, for example. Furthermore, the energy contained in the refrigerant can be ideally utilized by targeted reheating of the refrigerant or by using liquid separators in order to increase installation efficiency.

[0092] The diagram shown in FIG. 12 shows a clocked opening and closing of an expansion element during a time interval as another advantageous measure. In this way, a small amount of refrigerants evaporating on a heat exchanger can be fed to the latter when only a relatively low cold capacity is needed in order to maintain a temperature.

[0093] The diagram shown in FIG. 13 shows the exploitation of an overheating of the refrigerant in a suction line 66 of a compressor. An arrow 64 marks a heat exchanger, more precisely a course of a temperature increase as the refrigerant passes a heat exchanger surface 65 upstream of the suction line, more precisely its surface 66. By means of an electronic expansion element, a temperature is reduced downstream of the heat exchanger while an overheating in the suction line is ensured.