JP3604973B2 - Cascade type refrigeration equipment - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a cascade-type refrigeration apparatus that can be used for home / business refrigerators, ultra-low-temperature freezers, freezing showcases, physicochemical equipment, biomedical equipment, and the like.
[0002]
[Prior art]
Generally, a gas refrigerant is used in a refrigerating apparatus, and the gas refrigerant is cyclically compressed, condensed, expanded, and evaporated, and is frozen using heat of vaporization of the gas. Conventionally, CFCs have been used as a gas refrigerant, but when released into the atmosphere, they are decomposed by ultraviolet rays in the stratosphere, releasing chlorine atoms and destroying the ozone layer. For this reason, the use of harmful ultraviolet rays reaching the surface of the earth was banned because it increased.
As alternatives to CFCs, there are, for example, ammonia, carbon dioxide, sulfur dioxide, propane and the like. These can be used alone or in a mixture of propane and liquefied carbon dioxide at a predetermined ratio. No. 17040).
[0003]
[Problems to be solved by the invention]
When carbon dioxide gas is used alone as a refrigerant, the operating pressure (particularly, the condensing pressure) becomes extremely high, and the reliability of the component devices constituting the circulation circuit becomes a problem. In addition, when a flammable gas such as propane is used alone, there is a problem in that the gas leaks into a narrow closed space such as the inside of a refrigerator, which may cause an explosion.
[0004]
The present invention has been made to solve such a conventional problem, and does not require a high pressure such as carbon dioxide gas alone, and can prevent the danger of explosion due to the use of a flammable gas alone such as propane. It is intended to provide a device.
[0005]
[Means for Solving the Problems]
As a means for achieving this object, the present invention relates to a cascade type condenser having a common cascade condenser including a high-stage evaporator and a low-stage condenser, and forming a high-stage circulation circuit and a low-stage circulation circuit. In the refrigeration apparatus, a hydrocarbon-based refrigerant is used as the refrigerant in the high-stage circulation circuit, a carbon dioxide gas refrigerant is used as the refrigerant in the low-stage circulation circuit, and the carbon dioxide gas refrigerant in the low-stage circulation circuit is cooled to a certain temperature. An auxiliary condenser is provided before the low-stage condenser of the cascade condenser.
[0006]
The present invention can simultaneously solve the problem of the suppression of high-pressure operation and the danger of explosion by using a hydrocarbon-based refrigerant on the high stage side and a carbon dioxide gas refrigerant on the low stage side. Further, by providing an auxiliary capacitor before the low-stage cascade capacitor, an improvement in COP (coefficient of performance) can be expected.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a circuit block diagram showing a cascade refrigeration apparatus according to the present invention. A circulation circuit is formed on each of a high-stage side (outside the refrigerator) and a low-stage side (inside the refrigerator). The cascade condenser C including the low-stage condenser is common.
[0008]
The high-stage circulation circuit A is formed by connecting a high-stage compressor 1, a high-stage condenser 2, a high-stage expansion valve 3, and a high-stage evaporator 4 in series. The circulation circuit B is formed by connecting a low-stage compressor 5, a low-stage condenser 6, a low-stage expansion valve 7, and a low-stage evaporator 8 in series. Preferably, an auxiliary condenser 9 is connected between the unit 5 and the low-stage condenser 6.
[0009]
In the cascade refrigeration apparatus thus configured, a hydrocarbon-based refrigerant is used as the refrigerant in the high-stage circulation circuit A, and carbon dioxide gas is used as the refrigerant in the low-stage circulation circuit B.
[0010]
The working pressure becomes extremely high when carbon dioxide is used alone as a refrigerant. Heat exchange can be effectively utilized. Further, by using the hydrocarbon-based refrigerant on the high-stage side outside the refrigerator, the danger of explosion inside the refrigerator can be prevented.
[0011]
In the cascade condenser C, although not shown, heat exchange is performed only between the refrigerants via a double pipe (counterflow), that is, in an ideal state, the heat exchange between the high-stage evaporator 4 and the low-stage condenser 6 is performed. The heat exchange quantity is assumed to be equal. FIG. 2 is a diagram showing the relationship between pressure and enthalpy. Here, when the difference between the low-stage condensation temperature and the high-stage evaporation temperature (hereinafter ΔT) increases, the efficiency, that is, the coefficient of performance (COP) decreases. As described above, the COP can be improved by installing the auxiliary condenser 9 before the low-stage cascade condenser and cooling the refrigerant to a certain temperature.
[0012]
FIGS. 3A and 3B show the results of calculating the COP and the calorific value, respectively, using the low-stage evaporation temperature as a parameter. Here, the efficiency was compared with a single-stage circuit using propane or R404A in the deep temperature region and the case where the auxiliary capacitor 9 was not provided. As can be seen from FIG. 3 (b), higher efficiency can be expected by increasing the degree of superheat on the high-stage side. Although it is inferior in ℃, there is almost no difference in the region below -60 ℃, and it can be said that it is sufficiently practical. If the auxiliary condenser 9 is installed before the low-stage cascade condenser, a COP increase of 0.1 to 015 can be expected when the superheat degree of the high-stage evaporator is 10 deg.
[0013]
FIGS. 4 (a) and 4 (b) show the calculation results of the COP and the amount of heat when ΔT is used as a parameter. As is clear from FIG. 4A, it was confirmed that the COP had a peak point near ΔT = 5 ° C. Further, when the excluded volume ratio of the high-stage compressor 1 is set to 90% or 80%, it can be said that a larger COP can be obtained. It can be seen that when the displacement volume of the high-stage compressor 1 is reduced, the peak point of COP moves to the region where ΔT is small, and the absolute amount increases. Even in a refrigeration circuit using a natural refrigerant using propane in the upper stage and carbon dioxide gas in the lower stage in the cascade system, it is possible to obtain a COP equivalent to that of a refrigeration circuit suitable for the high-stage compressor.
Note that the present invention is not limited to the embodiment, and can be applied to a multi-refrigeration circuit.
[0014]
【The invention's effect】
As described above, according to the present invention, by using a hydrocarbon-based refrigerant on the high-stage side and a carbon dioxide gas refrigerant on the low-stage side of the cascade refrigeration system, high-pressure compression on the low-stage side used in the refrigerator is performed. Control and explosion danger can be solved at the same time. Further, by installing an auxiliary condenser before the condenser in the low-stage side circulation circuit, the COP (coefficient of performance) of the carbon dioxide gas refrigerant can be improved.
[Brief description of the drawings]
FIG. 1 is a circuit block diagram showing an example of a cascade refrigeration apparatus according to the present invention. FIG. 2 is a diagram showing a relationship between pressure and enthalpy. FIG. (A) is a diagram showing the relationship between the lower stage evaporation temperature and the COP, and (b) is a diagram showing the relationship between the lower stage evaporation temperature and the amount of heat. [FIG. 4] The difference between the lower stage condensation temperature and the higher stage evaporation temperature (ΔT ) Is a parameter, and (a) is a diagram showing the relationship between ΔT and COP, and (b) is a diagram showing the relationship between ΔT and the amount of heat.
DESCRIPTION OF SYMBOLS 1 ... High stage compressor 2 ... High stage condenser 3 ... High stage expansion valve 4 ... High stage evaporator 5 ... Low stage compressor 6 ... Low stage condenser 7 ... Low stage expansion valve 8 ... Low-stage evaporator 9 ... Auxiliary condenser A ... High-stage circulation circuit B ... Low-stage circulation path C ... Cascade condenser

Claims (1)

In a cascade refrigeration system in which a cascade condenser including a high-stage evaporator and a low-stage condenser is shared and a high-stage circulation circuit and a low-stage circulation circuit are formed, carbonization is performed as a refrigerant of the high-stage circulation circuit. Using a hydrogen-based refrigerant, using a carbon dioxide gas refrigerant as a refrigerant in the low-stage side circulation circuit, an auxiliary condenser for cooling the carbon dioxide gas refrigerant in the low-stage side circulation circuit to a certain temperature, the low-stage side condensation of the cascade condenser A cascade-type refrigeration system, which is installed in front of a vessel .

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