Vapor compression refrigeration system having ejector

Abstract

Piping, which connects between a radiator and an ejector, is covered with a thermal insulator to thermally insulate a refrigerant passage defined in the piping. Thus, it is possible to limit a reduction in enthalpy of refrigerant, which could be induced by cooling of high temperature refrigerant by low temperature atmosphere to lose the enthalpy before depressurization of the high temperature refrigerant through the ejector. As a result, it is possible to limit a reduction in a theoretical value of recoverable energy at the time of depressurization and expansion of the refrigerant.

Description

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is based on and incorporates herein by reference Japanese Patent Application No. 2002-134155 filed on May 9, 2002.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention generally relates to a vapor compression refrigeration system. More specifically, the present invention relates to a refrigeration system, i.e., an ejector cycle, which includes an ejector as a pumping means for circulating low pressure refrigerant through the ejector cycle.

[0004] 2. Description of Related Art

[0005] As defined in, for example, JIS Z8126 Number 2.1.2.3, an ejector is a kinetic energy transferring pump, which pumps and circulates fluid through use of entraining action of driving fluid that is discharged at high velocity through a nozzle of the ejector.

[0006] As is known in the art, the ejector cycle that includes such an ejector serves as a vapor compression refrigeration system, in which refrigerant is depressurized and expanded by the ejector to draw evaporated vapor phase refrigerant, which is evaporated in an evaporator, such that the ejector converts expansion energy (kinetic energy) of refrigerant to pressure energy to increase intake pressure of a compressor and thereby to reduce power consumption of the compressor.

[0007] In general, an ordinary vapor compression refrigeration system isentropically depressurizes refrigerant and includes a compressor as a single pumping means present in the system for circulating the refrigerant. Contrary to this, in the ejector cycle, refrigerant in a high pressure side of the ejector cycle is isentropically depressurized by the ejector. Furthermore, refrigerant in a low pressure side of the ejector cycle is circulated by pumping action of the ejector, and refrigerant in the high pressure side of the ejector cycle is circulated by the compressor.

SUMMARY OF THE INVENTION

[0008] It is an objective of the present invention to improve energy recovery through such an ejector of the vapor compression refrigeration system to improve an overall efficiency of the vapor compression refrigeration system.

[0009] To achieve the objective of the present invention, there is provided a vapor compression refrigeration system that transfers heat from a low temperature side to a high temperature side. The temperature of the high temperature side is higher than that of the low temperature side. The vapor compression refrigeration system includes a compressor, a radiator, an evaporator, an ejector and a refrigerant passage means for fluidly connecting between the radiator and the ejector. The compressor compresses refrigerant. The radiator cools high pressure refrigerant discharged from the compressor. The evaporator evaporates refrigerant. The ejector depressurizes and expands high pressure refrigerant supplied from the radiator to draw evaporated vapor phase refrigerant evaporated in the evaporator, such that the ejector converts expansion energy of refrigerant to pressure energy to increase intake pressure of the compressor. The refrigerant passage means is substantially, thermally insulated from a surrounding atmosphere that surrounds the refrigerant passage means.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:

[0011] FIG. 1 is a schematic diagram showing an ejector cycle according to a first embodiment of the present invention;

[0012] FIG. 2 is an enlarged schematic diagram showing an ejector of the ejector cycle;

[0013] FIG. 3 is a partial schematic perspective view of piping in the ejector cycle according to the first embodiment;

[0014] FIG. 4 is a p-h diagram showing relationship between pressure and enthalpy in the ejector cycle of FIG. 1;

[0015] FIG. 5 is a p-h diagram illustrating differences between a case with a thermal insulator and a case without the thermal insulator;

[0016] FIG. 6 is a table showing advantages of the ejector cycle according to the first embodiment;

[0017] FIG. 7 is a schematic diagram showing an ejector cycle according to a second embodiment of the present invention; and

[0018] FIG. 8 is a table showing advantages of the ejector cycle according to the second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0019] Various embodiments of the present invention will be described with reference to the accompanying drawings.

[0020] (First Embodiment)

[0021] A first embodiment of the present invention will be described with reference to FIGS. 1 to 6.

[0022] In the first embodiment of the present invention, an ejector cycle of the present invention is embodied in a showcase or refrigerator, which stores foods in a chilled state or in a frozen state. FIG. 1 schematically shows the ejector cycle of the present embodiment.

[0023] With reference to FIG. 1, a compressor 10 is driven by an electric motor to draw and compress refrigerant. A radiator 20 is a high-pressure side heat exchanger that exchanges heat between refrigerant, which is discharged from the compressor 10, and outside air, which is located outside of a storage compartment of the showcase or refrigerator, to cool refrigerant.

[0024] In the present embodiment, chlorofluorocarbon is used as refrigerant. Thus, the refrigerant pressure in the radiator 20 is kept less than the critical pressure of the refrigerant. When the refrigerant condenses in the radiator 20, the enthalpy of the refrigerant decreases. In place of the chlorofluorocarbon, carbon dioxide can be used as the refrigerant.

[0025] When carbon dioxide is used as the refrigerant, the refrigerant pressure in the radiator 20 becomes equal to or greater than the critical pressure of the refrigerant. Thus, the refrigerant temperature decreases without condensation of the refrigerant, and the enthalpy of the refrigerant decreases.

[0026] An evaporator 30 is a low-pressure side heat exchanger. In the evaporator 30, heat is exchanged between the liquid phase refrigerant and the air to be discharged into the compartment, so that the liquid phase refrigerant is vaporized or evaporated to cool the air to be discharged into the compartment. The ejector 40 depressurizes and expands the high pressure refrigerant to allow expansion of the refrigerant, so that the vapor phase refrigerant, which has been evaporated in the evaporator 30, is drawn into the ejector 40, and the expansion energy of the high pressure refrigerant is converted to the corresponding pressure energy to increase the intake pressure of the compressor 10.

[0027] As shown in FIG. 2, the ejector 40 includes a nozzle 41, a mixing chamber (or mixer) 42 and a diffuser 43. The nozzle 41 converts the pressure energy of the high pressure refrigerant to the velocity energy in such a manner that the refrigerant is isentropically depressurized and is expanded by the nozzle 41. In the mixing chamber 42, high velocity refrigerant flow discharged from the nozzle 41 draws the vapor phase refrigerant, which has been vaporized in the evaporator 30, into the mixing chamber 42 and is mixed with the vapor phase refrigerant. In the diffuser 43, the refrigerant discharged from the nozzle 41 and the refrigerant drawn from the evaporator 30 are further mixed in such a manner that the velocity energy of the refrigerant is converted to the pressure energy to increase the pressure of the refrigerant.

[0028] In the present embodiment, a Laval nozzle, which has a throttled portion in its passage, is used to increase the velocity of the refrigerant, which is discharged from the nozzle 41, to a level equal to or greater than the sonic velocity.

[0029] In the mixing chamber 42, the refrigerants are mixed in such a manner that the sum of the kinetic momentum of the refrigerant discharged from the nozzle 41 and the kinetic momentum of the refrigerant drawn into the ejector 40 from the evaporator 30 is conserved. Thus, even in the mixing chamber 42, the static pressure of the refrigerant is increased.

[0030] In the diffuser 43, a passage cross sectional area is linearly increased toward the downstream end of the diffuser 43 to convert the dynamic pressure of the refrigerant to the corresponding static pressure. Thus, in the ejector 40, the refrigerant pressure is increased through both the mixing chamber 42 and the diffuser 43. Therefore, the mixing chamber 42 and the diffuser 43 are collectively referred to as a pressurizer.

[0031] With reference to FIG. 1, the refrigerant discharged from the ejector 40 is supplied to a gas-liquid separator 50. The gas-liquid separator 50 serves as a gas-liquid separating means for separating and storing the refrigerant in two phases, i.e., the vapor phase refrigerant and the liquid phase refrigerant. A vapor phase refrigerant outlet of the gas-liquid separator 50 is connected to an inlet of the compressor 10, and a liquid phase refrigerant outlet of the gas-liquid separator 50 is connected to an inlet of the evaporator 30.

[0032] In the present embodiment, with reference to FIG. 1, piping 60 connects between the radiator 20 and the ejector 40 and forms a refrigerant passage. The piping 60 serves as a refrigerant passage means of the present invention for fluidly connecting between the radiator 20 and the ejector 40 by defining the refrigerant passage therein. With reference to FIGS. 1 and 3, the piping 60 is covered with a thermal insulator 61 and is thus thermally insulated from the atmosphere.

[0033] In the present embodiment, the thermal insulator 61 is made of a material, such as a resin material, a foam resin material or the like, which has a thermal conductivity lower than that of metals. Furthermore, in the present embodiment, the components, such as the compressor 10, the radiator 20 and the ejector 40, are received in the showcase. Thus, the above-described atmosphere refers to the atmosphere in the showcase.

[0034] FIG. 4 is a pressure-enthalpy (p-h) diagram showing macroscopic operation of the ejector cycle. The macroscopic operation of the ejector cycle of the present embodiment is substantially the same as that of the known ejector cycle. Thus, in the present embodiment, the macroscopic operation of the ejector cycle will not be discussed for the sake of simplicity. Furthermore, in FIG. 4, points indicated by numerals 1-7 correspond to points indicated by numerals 1-7 in FIG. 1 and show corresponding states of the refrigerant at these points 1-7.

[0035] At the time of increasing the refrigerant capacity, the rotational speed of the compressor 10 is increased to increase the refrigerant flow discharged from the compressor 10. On the other hand, at the time of decreasing the refrigerant capacity, the rotational speed of the compressor 10 is decreased to decrease the refrigerant flow discharged from the compressor 10.

[0036] Next, advantages of the present embodiment will be described.

[0037] In the ejector cycle, as shown in FIG. 5, the refrigerant is isentropically depressurized by the ejector 40, so that the corresponding enthalpy, which corresponds to adiabatic thermal head (simplified as “adia. thermal head” in FIG. 5) obtained upon the isentropic depressurization of the refrigerant by the ejector 40, is recovered to reduce power consumption of the compressor 10.

[0038] On the other hand, as is seen in the p-h diagram of FIG. 5, when the enthalpy decreases, the slope of the corresponding isentropic line is increased, i.e., is steepened, and thus the amount of change in the enthalpy, i.e., the adiabatic thermal head is reduced relative to the change in the pressure. Thus, the maximum theoretical value of recoverable energy at the time of depressurization and expansion of the refrigerant is reduced.

[0039] Contrary to this, in the present embodiment, the piping 60, which connects between the radiator 20 and the ejector 40, is covered with the thermal insulator 61. Thus, it is possible to limit a reduction in the enthalpy of the refrigerant, which could be induced by cooling of the high temperature refrigerant by the low temperature atmosphere to lose the enthalpy before depressurization of the high temperature refrigerant through the ejector 40. As a result, it is possible to limit a reduction in the theoretical value of the recoverable energy at the time of depressurization and expansion of the refrigerant.

[0040] This allows improvement in ejector performance, i.e., improvement in the amount of recovery of energy through the ejector 40 to reduce power consumption of the compressor 10, so that the ejector cycle can be more efficiently operated.

[0041] FIG. 6 shows comparison of two cases, i.e., the case where the piping 60 is covered with the thermal insulator 61 and the case where the piping 60 is not covered with the thermal insulator 61. As is shown in FIG. 6, the provision of the thermal insulator 61 around the piping 60 allows improvement in a coefficient of performance (COP).

[0042] (Second Embodiment)

[0043] With reference to FIGS. 7 and 8, a second embodiment of the present invention will be described.

[0044] As shown in FIG. 7, an internal heat exchanger 70 is provided. The internal heat exchanger 70 exchanges heat between the high pressure refrigerant, which is discharged from the radiator 20 and is to be supplied to the ejector 40, and the low pressure refrigerant to be supplied to the compressor 10. The internal heat exchanger 70 is inserted in piping 160, which serves as the refrigerant passage means and fluidly connects between the radiator 20 and the ejector 40. The piping 160 is covered with a thermal insulator 161 to thermally insulate the refrigerant passage from the atmosphere.

[0045] FIG. 8 shows comparison of two cases, i.e., the case where the piping 160 is covered with the thermal insulator 161 and the case where the piping 160 is not covered with the thermal insulator 161. As is shown in FIG. 8, the provision of the thermal insulator 161 around the piping 160 allows improvement in a coefficient of performance (COP).

[0046] When heat is exchanged between the high pressure refrigerant and the low pressure refrigerant through the internal heat exchanger 70, the enthalpy of the refrigerant supplied to the ejector 40 is reduced to reduce the ejector performance. However, since an enthalpy difference between the enthalpy of the refrigerant at the refrigerant inlet of the evaporator 30 and the enthalpy of the refrigerant at the refrigerant outlet of the evaporator 30 is increased, the heat absorbing capacity (refrigerating capacity) is increased.

[0047] (Other Embodiments)

[0048] As described above, the advantage of the present invention is further enhanced when the adiabatic thermal head is increased at the time of depressurization and expansion of the refrigerant. Thus, the present invention is particularly advantageous in the case of the vapor compression refrigeration system that requires the temperature (evaporation temperature) in the evaporator 30 to be equal to or less than 0 degrees Celsius. The example of such a vapor compression refrigeration system includes a freezer that requires the temperature in the freezer to be about −20 degrees Celsius.

[0049] In the above embodiments, the piping 60, 160 is covered with the thermal insulator 61, 161 to thermally insulate the refrigerant passage from the atmosphere. The present invention is not limited to this. For example, the piping 60, 160 itself can be made of a thermally insulating material. Alternatively, a thermally insulating sheet can be adhered around the piping 60, 160. Further alternatively, a thermally insulating material, such as a foam resin material, can be sprayed around the piping 60, 160. Also, the piping 60, 160 can be made of a combination of the thermally insulating material and a corrosion resisting material.

[0050] Furthermore, the temperature of the atmosphere, in which the piping 60, 160 is disposed, can be prevented from falling below the temperature of the atmosphere, in which the radiator 20 is disposed to minimize influence of the atmosphere on the refrigerant, which flows through the piping 60, 160, so that the refrigerant passage is thermally insulated from the atmosphere.

[0051] Furthermore, the refrigerant is not limited to the carbon dioxide or the chlorofluorocarbon. For example, the refrigerant can be hydrocarbon.

[0052] Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the above specific details.

Claims

1. A vapor compression refrigeration system that transfers heat from a low temperature side to a high temperature side, wherein the temperature of the high temperature side is higher than that of the low temperature side, the vapor compression refrigeration system comprising:

a compressor that compresses refrigerant;

a radiator that cools high pressure refrigerant discharged from the compressor;

an evaporator that evaporates refrigerant;

an ejector that depressurizes and expands high pressure refrigerant supplied from the radiator to draw evaporated vapor phase refrigerant evaporated in the evaporator, such that the ejector converts expansion energy of refrigerant to pressure energy to increase intake pressure of the compressor; and

a refrigerant passage means for fluidly connecting between the radiator and the ejector, wherein the refrigerant passage means is substantially, thermally insulated from a surrounding atmosphere that surrounds the refrigerant passage means.

2. A vapor compression refrigeration system according to claim 1, wherein the refrigerant passage means includes piping that is covered with a thermal insulator.

3. A vapor compression refrigeration system according to claim 1, further comprising a heat exchanger that exchanges heat between refrigerant, which is discharged from the radiator, and refrigerant to be supplied to the compressor, wherein the heat exchanger is inserted in the refrigerant passage means and is substantially, thermally insulated together with the refrigerant passage means from the surrounding atmosphere.

4. A vapor compression refrigeration system according to claim 1, wherein the refrigerant includes chlorofluorocarbon.

5. A vapor compression refrigeration system according to claim 1, wherein the refrigerant includes carbon dioxide.

6. A vapor compression refrigeration system according to claim 1, wherein the refrigerant includes hydrocarbon.

7. A vapor compression refrigeration system according to claim 1, wherein the pressure of the high pressure refrigerant discharged from the compressor is equal to or greater than a critical pressure of the refrigerant.

8. A vapor compression refrigeration system according to claim 1, wherein the vapor compression refrigeration system is disposed in an environment where the temperature of the surrounding atmosphere is normally substantially kept equal to or less than zero degrees Celsius during operation of the vapor compression refrigeration system.