COOLING UNIT USING TWO-STAGE COMPRESSOR

Abstract

 A cooling unit 1a includes a two-stage compressor 2a, a gas cooler 3, an intermediate cooler 6, a first decompressor 4 placed upstream of the intermediate cooler, a second decompressor 7 placed downstream of the intermediate cooler, an evaporator 8, and an oil separator 5, the oil separator 5 is placed between the intermediate cooler 6 and the first decompressor 4 which is located downstream of the gas cooler 3, the oil separator 5 separates oil 14 included in refrigerant 9, and the separated oil 14 is supplied to the two-stage compressor 2a. According to this, temperature of intermediate pressure refrigerant in the two-stage compressor 2a is lowered, density of inspired gas is increased, a refrigerant circulation amount can be increased, and the cooling unit has high cooling ability.

Description

[TECHNICAL FIELD]

[0001] The present disclosure relates to a cooling unit used for a conditioning unit which is utilized in a refrigeration system and an air conditioner and especially among them, the disclosure relates to a cooling unit using a two-stage compressor.

[BACKGROUND TECHNIQUE]

[0002] Patent document 1 discloses a cooling unit using a two-stage compressor. This cooling unit is provided with a two-stage compressor, an oil separator, a gas cooler, a first decompressor, an intermediate cooler, a second decompressor and an evaporator. They are provided in a refrigeration cycle. The cooling unit includes an oil cooler for cooling oil which is separated by the oil separator. The oil cooler is provided in an auxiliary cycle. When compressor exit pressure becomes higher than critical pressure in the refrigeration cycle which uses the two-stage compressor, a two-state expansion device and the intermediate cooler, the cooling unit performs control such that an opening degree of an expansion valve located upstream of the intermediate cooler is reduced. According to this, patent document 1 discloses that pressure in the intermediate cooler can be made lower than the critical pressure, gas refrigerant obtained by gas-liquid separating action of the intermediate cooler is sent to the compressor, and refrigerating ability is increased.

[PRIOR ART DOCUMENT]

[PATENT DOCUMENT]

[0003] [Patent Document 1] Japanese Patent Application Laid-open No.2017-172923

[SUMMARY OF THE INVENTION]

[PROBLEM TO BE SOLVED BY THE INVENTION]

[0004] The present disclosure supplies a cooling unit capable of obtaining higher refrigerating ability and high reliability as compared with the above conventional technique.

[MEANS FOR SOLVING PROBLEM]

[0005] A cooling unit of the present disclosure includes a two-stage compressor, a gas cooler, an intermediate cooler, a first decompressor placed upstream of the intermediate cooler, a second decompressor placed downstream of the intermediate cooler, an evaporator, and an oil separator, the oil separator is placed between the intermediate cooler and the first decompressor located downstream of the gas cooler, the oil separator separates oil included in refrigerant, and the separated oil is supplied to the two-stage compressor.

[EFFECT OF THE INVENTION]

[0006] In the cooling unit of the present disclosure, refrigerant is cooled by the gas cooler which is located upstream of the oil separator and which has a heat radiation area larger than that of the oil cooler, and oil in the refrigerant is returned from the oil separator into the two-stage compressor. Therefore, temperature of intermediate pressure refrigerant in the two-stage compressor is lowered, and temperature of inspired gas of a second compression mechanism is lowered. Hence, inspired gas density of the second compression mechanism is increased, and a refrigerant circulation amount can be increased. At this time, temperature of discharged gas is also lowered. Therefore, it is possible to obtain a cooling unit having high cooling ability and high reliability. Further, an oil cooler is also unnecessary and thus, production costs can be reduced, and it is possible to provide an inexpensive cooling unit.

[BRIEF DESCRIPTION OF THE DRAWINGS]

[0007] 

Fig. 1 is a circuit configuration diagram showing a refrigeration cycle of a cooling unit in a first embodiment;

Fig. 2 is a p-h diagram for describing a cycle of the cooling unit in the first embodiment;

Fig. 3 is a circuit configuration diagram showing a refrigeration cycle of a cooling unit in a second embodiment; and

Fig. 4 is a p-h diagram for describing a cycle of the cooling unit in the second embodiment.

[MODE FOR CARRYING OUT THE INVENTION]

(Knowledge and the like which became basis of the present disclosure)

[0008] When the present inventors arrived at the present disclosure, a cooling unit using a compressor having a structure in which an external cooler such as an intercooler could not be mounted could not obtain high cooling ability.

[0009] Especially, in the case of a cooling unit in which a first compression mechanism and a second compression mechanism are integrally formed together and a two-stage compressor which cannot independently control respective refrigerant circulation amounts is used, it is not possible to control temperature of inspired gas of the second compression mechanism, there is tendency that temperature of the inspired gas becomes relatively high, and density of the inspired gas is reduced and therefore, the amount of refrigerant circulation is reduced, and temperature of discharged gas also rises. Therefore, high cooling ability cannot be obtained and reliability is also deteriorated.

[0010] Hence, it is objects to the cooling unit having a configuration disclosed in patent document 1 to separate oil discharged together with refrigerant from a discharge portion of the second compression mechanism from the refrigerant by the oil separator before the oil reaches the gas cooler, and to secure oil level in the compressor. According to this cooling unit, oil is returned into the two-stage compressor by the auxiliary cycle, the auxiliary cycle is provided with an oil cooler, oil is cooled by the oil cooler, the oil is returned into the two-stage compressor, and refrigerant having intermediate pressure in the two-stage compressor is cooled. According to this, temperature of the inspired gas of the second compression mechanism is lowered, the density of the inspired gas is increased, and the amount of the refrigerant circulation is increased. At this time, since temperature of discharged gas is also lowered, cooling ability is enhanced.

[0011] However, it is difficult to install an oil cooler having a sufficiently large heat radiation area in a limited space, i.e., cooling unit and therefore, it is not possible to sufficiently cool the oil. As a result, it is not also possible to sufficiently cool refrigerant of intermediate pressure in the two-stage compressor, and a cooling unit having high cooling ability and high reliability cannot be obtained. Further, costs of members of the oil cooler itself, mounting steps and costs are increased, and there is a problem that production costs are largely increased.

[0012] Installation of the above oil cooler has the same problems even when a two-stage compressor on which a cooler such as an intercooler can be mounted is used, e.g., even when a two-stage compressor in which refrigerant of intermediate pressure compressed by a first-stage compressor is discharged to outside and suction of a second-stage compressor is directly sucked from outside is used.

[0013] Under such severe conditions, the present inventors arrived at an idea that it might be possible to share a cooling operation of oil with a gas cooler having a large heat radiation area. Then, the inventors arrived at a subject matter of the present disclosure based on this idea.

[0014] Hence, the present disclosure provides, as a configuration in which the cooling operation is shared with the gas cooler having a large heat radiation area, a cooling unit capable of inexpensively obtaining higher cooling ability and higher reliability than those of the conventional techniques.

[0015] An embodiment will be described below in detail with reference to the drawings. However, description which is detail more than necessary is omitted in some cases. For example, detailed description of matters which are already known, or redundant description of substantially the same configuration is omitted in some cases.

[0016] Accompanying drawings and the following descriptions are provided so that a person skilled in the art can sufficiently understand the present disclosure, and it is not intended that subject matters described in claims are limited by the accompanying drawings and the following descriptions.

(First Embodiment)

[0017] A first embodiment will be described below using Figs. 1 and 2.

[1-1. Configuration]

[0018] As shown in Fig. 1, in a cooling unit 1a, a known two-stage compression two-stage expansion refrigeration cycle circuit is configured by placing a two-stage compressor 2a, a gas cooler 3, a first decompressor 4, an oil separator 5, an intermediate cooler 6, a second decompressor 7 and an evaporator 8 in this order. Refrigerant (e.g., carbon dioxide) 9 is charged into the refrigeration cycle circuit.

[0019] The two-stage compressor 2a includes a first compression mechanism 11a, a second compression mechanism 12a, an electric motor 13 and oil 14, and they are provided in a container 10. The first compression mechanism 11a and the second compression mechanism 12a are connected to each other through a shaft 15, and the compression mechanism 11a and 12a are driven by an electric motor 13.

[0020] The first compression mechanism 11a and the second compression mechanism 12a suck and compress refrigerant 9. Pressure of the refrigerant 9 compressed by the first compression mechanism 11a becomes intermediate pressure, and the refrigerant is released into the container 10. The second compression mechanism 12a sucks intermediate pressure refrigerant 9 existing in the container 10, and further compresses the refrigerant 9 to high pressure, and discharges the refrigerant 9 into the known two-stage compression two-stage expansion refrigeration cycle together with oil 14.

[0021] The gas cooler 3 exchanges heat of the refrigerant 9 compressed by the second compression mechanism 12a with outside air or the like, and cools the refrigerant 9, and the refrigerant 9 is decompressed by the first decompressor 4.

[0022] A gas-liquid separation type oil separator is used as the oil separator 5, and the oil separator 5 is placed between the first decompressor 4 and the intermediate cooler 6. The oil 14 separated by the oil separator 5 is returned into the container 10 of the two-stage compressor 2a.

[0023] The refrigerant 9 which is decompressed by the first decompressor 4 and separated by the oil separator 5 is introduced into the intermediate cooler 6. A portion of the refrigerant 9 which is cooled by the intermediate cooler 6 is returned into the container 10 of the two-stage compressor 2a, and this refrigerant 9 is mixed, in the container 10, with another refrigerant 9 which is compressed by the first compression mechanism 11a and whose pressure becomes intermediate pressure. The mixed refrigerant 9 is sucked into a suction part (not shown) of the second compression mechanism 12a.

[0024] Remaining refrigerant 9 which is cooled by the intermediate cooler 6 is further decompressed by the second decompressor 7, it passes through the evaporator 8, and it is directly sucked into the suction part (not shown) of the first compression mechanism 11a in the container 10 of the two-stage compressor 2a.

[0025] Both the first decompressor 4 and second decompressor 7 are composed of electric expansion valves whose opening degrees (decomposition amounts) are variable.

[1-2. Operation]

[0026] Operation and effect of the cooling unit 1a constructed as described above will be described below.

[0027] Operation of the cooling unit 1a will be described based on Figs. 1 and 2.

[0028] A refrigeration cycle of the cooling unit 1a will be described together with a p-h diagram shown in Fig. 2. In Fig. 2, a character a shows a saturated liquid line, and a character b shows a saturated vapor line.

[0029] First, in the first compression mechanism 11a, the refrigerant 9 is compressed to predetermined intermediate pressure (process of symbols A -> B in Fig. 2). After the refrigerant 9 is compressed to the intermediate pressure, the refrigerant 9 is released into the container 10.

[0030] Next, the intermediate pressure refrigerant 9 released into the container 10 is compressed to predetermined high pressure by the second compression mechanism 12a (process of symbols C -> D), and the refrigerant 9 is discharged to the gas cooler 3. Next, the refrigerant 9 discharged to the gas cooler 3 exchanges heat with outside air, and is cooled to predetermined temperature (process of symbols D -> E). At this time, in the gas cooler 3, oil 14 includes in the refrigerant 9 is also cooled together with the refrigerant 9. Thereafter, the refrigerant 9 is decompressed by the first decompressor 4 (symbols E -> F), and the refrigerant 9 flows into the oil separator 5 together with the oil 14.

[0031] The oil 14 cooled by the gas cooler 3 is separated by the oil separator 5, and the oil 14 is returned into the container 10 of the two-stage compressor 2a. The oil 14 cools refrigerant 9 and the like which are compressed to the intermediate pressure in the first compression mechanism 11a, the second compression mechanism 12a, the electric motor 13 and the container 10.

[0032] The refrigerant 9 decompressed by the first decompressor 4 and separated by the oil separator 5 flows into the intermediate cooler 6, and the refrigerant 9 is further cooled (symbols F -> G). Thereafter, a portion of intermediate pressure refrigerant 9 is returned into the container 10 of the two-stage compressor 2a (symbols G -> B), and is mixed with intermediate pressure refrigerant 9 in the container 10. Further, the intermediate pressure refrigerant 9 in the container 10 is cooled (process of symbols B -> C), and is sucked into the second compression mechanism 12a.

[0033] Here, when the oil separator 5 is placed upstream of the gas cooler 3 like the conventional technique, it is necessary to provide an oil cooler (not shown) for cooling the oil 14. From a viewpoint of an installation space and the like in the cooling unit 1a, a heat radiation area of the oil cooler becomes smaller than that of the gas cooler 3, and the oil 14 cannot sufficiently be cooled. Therefore, intermediate pressure refrigerant 9 in the container 10 also cannot sufficiently be cooled (process of symbols B -> C').

[0034] However, in the case of the cooling unit 1a of the present disclosure, the oil separator 5 is located downstream of the gas cooler 3 as described above, and the oil 14 in the refrigerant 9 is cooled by the gas cooler 3 together with the refrigerant 9. Since the gas cooler 3 has a sufficient area, the oil 14 is efficiently cooled. After the oil 14 is decompressed by the first decompressor 4, the oil 14 is supplied into the container 10 through the oil separator 5.

[0035] That is, the intermediate pressure refrigerant 9 in the container 10 of the two-stage compressor 2a is cooled by oil 14 which is cooled by the gas cooler 3 and a portion of the intermediate pressure refrigerant 9 which is cooled by the gas cooler 3 and the intermediate cooler 6. Hence, temperature of the inspired gas of the second compression mechanism 12a is largely lowered, and density of the inspired gas of the second compression mechanism 12a is increased. According to this, a refrigerant circulation amount is increased. At this time, since temperature of discharged gas is also lowered, F in Fig. 2 becomes lower than F' of conventional technique.

[0036] Hence, enthalpy of the refrigerant 9 which flows through a refrigerant flow passage is further reduced (process of symbols F' -> G', and F -> G). That is, a variation amount of enthalpy in the process of symbols H -> A becomes larger than a variation amount of enthalpy in conventional technique (symbols H' -> A).

[0037] Since the cooling unit 1a of the present disclosure is the two-stage compression two-stage expansion refrigeration cycle, the first decompressor 4 can control such that density of refrigerant 9 which flows into the oil separator 5 becomes smaller than density of oil 14 which flows into the oil separator 5. Therefore, it is possible to reliably separate the oil 14 from the refrigerant 9, and more refrigerant can be circulated.

[0038] Remaining intermediate pressure refrigerant 9 which passes through the intermediate cooler 6 is further decompressed (symbols G -> H) by the second decompressor 7 and flows into the evaporator 8.

[1-3. Effect and the like]

[0039] As described above, in the first embodiment, the cooling unit 1a includes the two-stage compressor 2a, the gas cooler 3, the intermediate cooler 6, the first decompressor 4 placed upstream of the intermediate cooler 6, the second decompressor 7 placed downstream of the intermediate cooler 6, the evaporator 8, and the oil separator 5, the oil separator 5 is placed between the intermediate cooler 6 and the first decompressor 4 located downstream of the gas cooler 3, the oil separator 5 separates oil 14 included in refrigerant 9, and the separated oil 14 is supplied to the two-stage compressor 2a.

[0040] The oil separator 5 is placed between the intermediate cooler 6 and the first decompressor 4 located downstream of the gas cooler 3 as described above. In other words, the oil separator 5 is placed downstream of the gas cooler 3. According to this, low temperature oil 14 which radiates heat in the gas cooler 3 having a large heat radiation area can be returned into the container 10 of the two-stage compressor 2a from the oil separator 5. As a result, temperatures of the intermediate pressure refrigerant 9 in the two-stage compressor 2a, the first compression mechanism 11a, the second compression mechanism 12a and the electric motor 13 are lowered, and inhalation superheat of the second compression mechanism 12a is lowered. Hence, inhalation density of the second compression mechanism 12a is increased, and the circulation amount can be increased. At this time, discharged gas temperature is also lowered.

[0041] According to this, it is possible to provide a cooling unit 1a having high cooling ability and high reliability.

[0042] That is, by returning the low temperature oil 14 which radiates heat in the gas cooler 3 having the large heat radiation area into the two-stage compressor 2a from the oil separator 5, the intermediate pressure refrigerant in the two-stage compressor can efficiently be cooled, and inspired gas temperature of the second compression mechanism 12a is lowered. According to this, since the density of the inspired gas is increased, the refrigerant circulation amount is increased, and the cooling unit has higher cooling ability as compared with the conventional technique. At this time, since the discharged gas temperature is also lowered, reliability of the cooling unit is also enhanced.

[0043] Further, since an oil cooler (not shown) is unnecessary, the production costs can be reduced, and it is possible to provide an inexpensive cooling unit 1a.

[0044] As shown in the first embodiment, in this cooling unit 1a, the first decompressor 4 controls pressure of the refrigerant 9 such that density of refrigerant 9 which flows into the oil separator 5 becomes smaller than density of the oil 14 which flows into the oil separator 5. That is, the first decompressor 4 controls such that the density of the refrigerant 9 which flows into the oil separator 5 becomes lower than the density of the oil 14 which flows into the oil separator 5, and the refrigerant 9 and the oil 14 are returned into the two-stage compressor from the intermediate cooler 6. According to this, a density difference between the refrigerant 9 and the oil 14 is secured.

[0045] By securing this density difference between the refrigerant 9 and the oil 14, separation between the refrigerant 9 and the oil 14 is facilitated, and more refrigerant can be circulated. Therefore, it is possible to provide a cooling unit 1a which can exhibit higher cooling ability.

[0046] The two-stage compressor 2a shown in the first embodiment has such a structure that refrigerant 9 which is compressed to the intermediate pressure by the first compression mechanism 11a is released into the container 10, and this released refrigerant 9 is sucked as it is from the suction part (not shown) of the second compression mechanism 12a. Hence, a cooling device such as an intercooler (not shown) cannot be attached. The configuration of the present disclosure exhibits a large effect when the cooling unit 1a using the two-stage compressor 2a having such a structure cools the intermediate pressure refrigerant 9.

(Second Embodiment)

[0047] A second embodiment will be described below using Figs. 3 and 4. The same symbols will be allocated to the same members or corresponding members as those of the first embodiment.

[2-1. Configuration]

[0048] As shown in Fig. 3, in a cooling unit 1b, a known two-stage compression two-stage expansion refrigeration cycle circuit is configured by placing a two-stage compressor 2b, a gas cooler 3, a first decompressor 4, an oil separator 5, an intermediate cooler 6, a second decompressor 7 and an evaporator 8 in this order. Refrigerant (e.g., carbon dioxide) 9 is charged into the refrigeration cycle circuit.

[0049] The two-stage compressor 2b includes a first compression mechanism 11b, a second compression mechanism 12b, an electric motor 13 and oil 14, and they are provided in an container 10. The first compression mechanism 11b and the second compression mechanism 12b are connected to a shaft 15, and these compression mechanisms 11b and 12b are driven by an electric motor 13.

[0050] The first compression mechanism 11b and the second compression mechanism 12b suck and compress refrigerant 9. Pressure of the refrigerant 9 compressed by the first compression mechanism 11b becomes intermediate pressure, and the refrigerant is released into the container 10. Thereafter, the refrigerant 9 is once discharged to outside of the container 10, the refrigerant 9 passes through an intercooler 16 provided in a refrigerant circuit which connects the first compression mechanism 11b and the second compression mechanism 12b to each other, and the refrigerant 9 is sucked directly into a suction part (not shown) of the second compression mechanism 12b. The refrigerant 9 is compressed to high pressure, and is discharged to a known two-stage compression two-stage expansion refrigeration cycle circuit together with the oil 14.

[0051] The gas cooler 3 exchanges heat of the refrigerant 9 compressed by the second compression mechanism 12b with outside air or the like, and cools the refrigerant 9, and the refrigerant 9 is decompressed by the first decompressor 4.

[0052] A gas-liquid separation type oil separator is used as the oil separator 5, and the oil separator 5 is placed between the first decompressor 4 and the intermediate cooler 6. The oil 14 separated by the oil separator 5 is returned into the container 10 of the two-stage compressor 2b.

[0053] The refrigerant 9 which is decompressed by the first decompressor 4 and separated by the oil separator 5 is introduced into the intermediate cooler 6. A portion of the refrigerant 9 which is cooled by the intermediate cooler 6 joins up with another refrigerant 9 which passes through the intercooler 16, and they are sucked directly into a suction part (not shown) of the second compression mechanism 12b in the container 10 of the two-stage compressor 2b.

[0054] Remaining refrigerant 9 which is cooled by the intermediate cooler 6 is further decompressed by the second decompressor 7, it passes through the evaporator 8, and it is sucked directly into the suction part (not shown) of the first compression mechanism 11b in the container 10 of the two-stage compressor 2b.

[0055] Both the first decompressor 4 and second decompressor 7 are composed of electric expansion valves whose opening degrees (decomposition amounts) are variable.

[2-2. Operation]

[0056] Operation and effect of the cooling unit 1b constructed as described above will be described below.

[0057] Operation of the cooling unit 1b will be described based on Figs. 3 and 4.

[0058] A refrigeration cycle of the cooling unit 1b will be described together with a p-h diagram shown in Fig. 4. In Fig. 4, a character a shows a saturated liquid line, and a character b shows a saturated vapor line.

[0059] First, in the first compression mechanism 11b, the refrigerant 9 is compressed to predetermined intermediate pressure (process of symbols A -> B in Fig. 4), the refrigerant 9 is released into the container 10 and then, the refrigerant 9 is once discharged to outside of the container 10, the refrigerant 9 passes through the intercooler 16 and it is cooled (symbols B -> C).

[0060] Next, the refrigerant 9 which is cooled by the intercooler 16 is sucked directly into the suction part (not shown) of the second compression mechanism 12b, the refrigerant 9 is further compressed to high pressure (process symbols C -> D), and the refrigerant 9 is discharged to the known two-stage compression two-stage expansion refrigeration cycle circuit together with the oil 14.

[0061] Next, the refrigerant 9 discharged to the gas cooler 3 of the two-stage compression two-stage expansion refrigeration cycle circuit exchanges heat with outside air and the like, and the refrigerant 9 is cooled to predetermined temperature (process symbols D -> E) . At this time, in the gas cooler 3, the refrigerant 9 and also the oil 14 included in the refrigerant 9 are cooled. Thereafter, the refrigerant 9 is decompressed by the first decompressor 4 (symbols E -> F), and the refrigerant 9 flows into the oil separator 5 together with the oil 14.

[0062] Next, the oil 14 cooled by the gas cooler 3 is separated by the oil separator 5, and the oil 14 is returned into the container 10 of the two-stage compressor 2b. The oil 14 cools refrigerant 9 and the like which are compressed to the intermediate pressure in the first compression mechanism 11b, the second compression mechanism 12b, the electric motor 13 and the container 10.

[0063] The refrigerant 9 decompressed by the first decompressor 4 and separated by the oil separator 5 flows into the intermediate cooler 6, and the refrigerant 9 is further cooled (symbols F -> G). Thereafter, a portion of intermediate pressure refrigerant 9 joins up with another refrigerant 9 which is cooled by the intercooler 16, and they are sucked directly into the suction part of the second compression mechanism 12b in the container 10 of the two-stage compressor 2b (symbols G -> C).

[0064] Here, when the oil separator 5 is placed upstream of the gas cooler 3 as in the conventional technique, it is necessary to provide an oil cooler (not shown) for cooling the oil 14. Further, from a viewpoint of an installation space and the like in the cooling unit 1b, a heat radiation area of the oil cooler becomes smaller than that of the gas cooler 3, and the oil 14 cannot sufficiently be cooled. Therefore, intermediate pressure refrigerant 9 in the container 10 also cannot sufficiently be cooled (process of symbols B -> C').

[0065] However, in the case of the cooling unit 1b of the present disclosure, the oil separator 5 is located downstream of the gas cooler 3 as described above, and the oil 14 in the refrigerant 9 is cooled by the gas cooler 3 together with the refrigerant 9. Since the gas cooler 3 has a sufficient area, the oil 14 is efficiently cooled. After the oil 14 is decompressed by the first decompressor 4, the oil 14 is supplied into the container 10 through the oil separator 5.

[0066] That is, the intermediate pressure refrigerant 9 in the container 10 of the two-stage compressor 2b is cooled by the oil 14 which is cooled by the gas cooler 3. Since this gas cooler 3 has a sufficient area, the oil 14 is efficiently cooled as described above. The cooled intermediate pressure refrigerant 9 in the container 10 is once discharged to outside of the container 10, and the refrigerant 9 is further cooled by the intercooler 16. Thereafter, the refrigerant 9 joints up with a portion of another intermediate pressure refrigerant 9 which is cooled by the intermediate cooler 6, and they are sucked directly into the suction part (not shown) of the second compression mechanism 12b. Therefore, temperature of the inspired gas is largely lowered, density of the inspired gas of the second compression mechanism 12b is increased, and the refrigerant circulation amount can be increased. At this time, since temperature of the discharged gas is also lowered, F in Fig. 4 becomes lower than F' of conventional technique.

[0067] Hence, enthalpy of the refrigerant 9 which flows through a refrigerant flow passage is further reduced (process of symbols F' -> G', and F -> G). That is, a variation amount of enthalpy in the process of symbols H -> A becomes larger than a variation amount of enthalpy in conventional technique (symbols H' -> A).

[0068] Since the cooling unit 1b of the present disclosure is the two-stage compression two-stage expansion refrigeration cycle, the first decompressor 4 can control such that density of refrigerant 9 which flows into the oil separator 5 becomes smaller than density of oil 14 which flows into the oil separator 5. Therefore, it is possible to reliably separate the oil 14 from the refrigerant 9, and more refrigerant can be circulated.

[0069] Intermediate pressure refrigerant 9 which passes through the intermediate cooler 6 is further decompressed (symbols G -> H) by the second decompressor 7 and flows into the evaporator 8.

[2-3. Effect and the like]

[0070] As described above, in the second embodiment, the cooling unit 1b includes: the two-stage compressor 2b; the gas cooler 3; the intermediate cooler 6; the first decompressor 4 placed upstream of the intermediate cooler 6; the second decompressor 7 placed downstream of the intermediate cooler 6; the evaporator 8; the oil separator 5; and the intercooler 16 provided in the refrigerant circuit which connects the first compression mechanism 11b and the second compression mechanism 12b of the two-stage compressor 2b, wherein the oil separator 5 is placed between the intermediate cooler 6 and the first decompressor 4 located downstream of the gas cooler 3, oil 14 included in the refrigerant 9 is separated by the oil separator 5, and the separated oil 14 is supplied to the two-stage compressor 2b.

[0071] Since the cooling unit 1b is configured as described above, low temperature oil 14 which radiates heat in the gas cooler 3 having a large heat radiation area is returned from the oil separator 5 into the container 10 of the two-stage compressor 2b. According to this, temperatures of the intermediate pressure refrigerant 9 in the two-stage compressor 2b, the first compression mechanism 11b, the second compression mechanism 12b and the electric motor 13 are lowered. Therefore, in a state where temperature of the intermediate pressure refrigerant 9 in the container 10 is low, the refrigerant 9 is discharged to outside of the container 10, and is further cooled by the intercooler 16. The low temperature refrigerant 9 joins up with a portion of intermediate pressure another refrigerant 9 which is cooled by the intermediate cooler 6, and they are sucked directly into the suction part (not shown) of the second compression mechanism 12b. Hence, temperature of the inspired gas is largely lowered, density of the inspired gas of the second compression mechanism 12b is increased, and the refrigerant circulation amount can be increased. At this time, temperature of discharged gas is also lowered.

[0072] That is, the cooling unit shown in the second embodiment is characterized in that the intercooler 16 for cooling refrigerant 9 which is discharged from the first compression mechanism 11b is further provided in the refrigerant circuit which connects, to each other, the first compression mechanism 11b and the second compression mechanism 12b of the two-stage compressor 2b of the cooling unit described in the first embodiment.

[0073] According to this, by cooling refrigerant 9 compressed by the first compression mechanism 11b and by returning the refrigerant 9 into the two-stage compressor 2b, temperature of the inspired gas of the second compression mechanism 12b is further lowered, and density of the inspired gas is further increased. Therefore, the refrigerant circulation amount is further increased. At this time, temperature of discharged gas is further lowered. According to this, it is possible to obtain higher cooling ability and higher reliability as compared with the cooling unit of the first embodiment.

[0074] Further, an oil cooler (not shown) is also unnecessary and thus, production costs can be reduced, and it is possible to provide an inexpensive cooling unit 1b.

[0075] Like the first embodiment, according to this cooling unit 1b, the first decompressor 4 controls pressure of refrigerant 9 such that density of refrigerant 9 which flows into the oil separator 5 becomes smaller than density of oil 14 which flows into the oil separator 5. That is, the first decompressor 4 controls such that density of refrigerant 9 which flows into the oil separator 5 becomes smaller than density of oil 14 which flows into the oil separator 5, and the refrigerant 9 and the oil 14 are returned to the two-stage compressor from the intermediate cooler 6. According to this, a density difference between the refrigerant 9 and the oil 14 is secured.

[0076] By securing this density difference between the refrigerant 9 and the oil 14, separation between the refrigerant 9 and the oil 14 is facilitated, and more refrigerant can be circulated. Therefore, it is possible to provide a cooling unit 1b which can exhibit higher cooling ability.

[0077] As described above, the first and second embodiments were described as examples of the technique disclosed in the present application. However, the technique in the present disclosure is not limited to them, and the technique can also be applied to another embodiment in which change, replacement, addition or omission is carried out.

[INDUSTRIAL APPLICABILITY]

[0078] According to the cooling unit using the two-stage compressor, the two-stage expansion device and the intermediate cooler, cooling ability and reliability can be enhanced, and it is possible to suppress the rise in member costs and production costs. Therefore, the cooling unit can be applied to a refrigeration system and an air conditioner.

[EXPLANATION OF SYMBOLS]

[0079] 

1a, 1b

cooling unit

2a, 2b

two-stage compressor

3

gas cooler

4

first decompressor

5

oil separator

6

intermediate cooler

7

second decompressor

8

evaporator

9

refrigerant

10

container

11a, 11b

first compression mechanism

12a, 12b

second compression mechanism

13

electric motor

14

oil

15

shaft

16

intercooler

Claims

1. A cooling unit using a two-stage compressor, comprising

the two-stage compressor,

a gas cooler,

an intermediate cooler,

a first decompressor placed upstream of the intermediate cooler,

a second decompressor placed downstream of the intermediate cooler,

an evaporator, and

an oil separator, wherein

the oil separator is placed between the intermediate cooler and the first decompressor located downstream of the gas cooler,

the oil separator separates oil included in refrigerant, and

the separated oil is supplied to the two-stage compressor.

2. The cooling unit using the two-stage compressor according to claim 1, wherein the first decompressor controls such that density of the refrigerant which flows into the oil separator becomes smaller than density of the oil which flows into the oil separator.

3. The cooling unit using the two-stage compressor according to claim 1 or 2, wherein a refrigerant circuit which connects a first compression mechanism and a second compression mechanism of the two-stage compressor to each other is provided with an intercooler which cools the refrigerant discharged from the first compression mechanism.

Drawing