JP2001091074A - Cascade-type refrigerating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cascade-type refrigerating device that does not require high pressure needed at individual use of a carbon dioxide refrigerant, and at the same time, can prevent the risk of explosion when a propane refrigerant used individually. SOLUTION: A cascade capacitor C including a high-stage-side (the outside of the refrigerating device) evaporator 4 and a low-stage side (the inside of the device) condenser 6 is shared, and high-stage side circulation circuit A and a low-stage side circulation path B are formed, thus composing a cascade- type binary refrigerating circuit. As the refrigerant of the high-stage side circulation path A, a natural system refrigerant (a hydrocarbon system such as propane and ammonia) is used, and a carbon dioxide is used as the refrigerant of the low-stage side circulation path B. An auxiliary capacitor 9 for cooling the refrigerant by a fixed temperature is installed in front of a low-stage side condenser 6 of the cascade capacitor C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cascade refrigeration apparatus which can be used for household / business refrigerators, ultra-low temperature freezers, freezer showcases, physics and chemistry equipment, biomedical equipment and the like.

[0002]

2. Description of the Related Art Generally, a gas refrigerant is used in a refrigerating apparatus, and the gas refrigerant is compressed, condensed, expanded and evaporated in a cyclic manner, and is frozen by utilizing 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 light in the stratosphere, releasing chlorine atoms and destroying the ozone layer. For this reason, the use of harmful ultraviolet rays reaching the ground surface has been banned due to an increase. 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 (Japanese Unexamined Patent Publication No. No. 17040).

[0003]

When carbon dioxide gas is used alone as a refrigerant, the operating pressure (especially the condensing pressure) becomes extremely high, and the reliability of the components 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 and there is a risk of explosion.

The present invention has been made to solve such a conventional problem, and does not require high pressure such as carbon dioxide alone, and can prevent the danger of explosion due to the use of flammable gas such as propane alone. It is an object to provide a cascade refrigeration apparatus.

[0005]

As technical means for achieving this object, the present invention provides a natural refrigerant,
The gist is a cascade refrigeration system that uses carbon dioxide gas refrigerant on the lower stage side. Further, the cascade condenser including the high-stage evaporator and the low-stage condenser is commonly used, a high-stage circulation circuit and a low-stage circulation circuit are formed, and a natural refrigerant is used as the refrigerant in the high-stage circulation passage. The gist of the present invention is to use a carbon dioxide gas refrigerant as a refrigerant in the low-stage side circulation path. Furthermore, the gist is to use a hydrocarbon-based refrigerant as the refrigerant in the high-stage circulation path, and to install an auxiliary condenser for cooling the refrigerant to a certain temperature before the low-stage condenser of the cascade condenser. Things.

According to the present invention, the use of a natural refrigerant such as a hydrocarbon-based refrigerant on the high stage side and the use of carbon dioxide gas refrigerant on the low stage side can simultaneously suppress the problem of high pressure operation and the danger of explosion. Also, by providing an auxiliary capacitor before the low-stage cascade capacitor, an improvement in COP (coefficient of performance) can be expected.

[0007]

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.

The high-stage side circulation circuit A includes a high-stage side compressor 1
The high-stage condenser 2, the high-stage expansion valve 3, and the high-stage evaporator 4 are connected in series. The low-stage circulation circuit B includes a low-stage compressor 5 and a low-stage compressor. A condenser 6, a low-stage expansion valve 7,
It is formed by connecting the low-stage evaporator 8 in series and further comprises an auxiliary condenser 9 between the low-stage compressor 5 and the low-stage condenser 6.
Are preferably connected.

In the cascade refrigeration system thus configured, a natural refrigerant (for example, a hydrocarbon system such as propane or methane or ammonia gas) is used as the refrigerant in the high-stage circulation circuit A, The circulation circuit B uses carbon dioxide gas as a refrigerant.

[0010] When carbon dioxide is used alone as a refrigerant, the operating pressure becomes extremely high. However, in the present invention, the operating pressure is kept low by using carbon dioxide on the lower stage side of the cascade circuit, so that it can be used in a low temperature range peculiar to carbon dioxide. The good heat exchange property of can be effectively used. Further, by using the natural refrigerant on the high-stage side outside the refrigerator, the danger of explosion in the refrigerator can be prevented.

In the cascade condenser C, although not shown, heat exchange is performed only between the refrigerants through a double pipe (counter flow), that is, in an ideal state, the high-stage evaporator 4 and the low-stage condenser are exchanged. 6 and the exchange heat quantity is equal. FIG.
Is a diagram showing the relationship between pressure and enthalpy, where the difference between the low-stage condensation temperature and the high-stage evaporation temperature (hereinafter, Δ
As T) increases, the efficiency, that is, the coefficient of performance (COP) decreases. However, as described above, it is possible to improve the COP by installing the auxiliary condenser 9 in front of the low-stage cascade condenser and cooling the refrigerant to a certain temperature. It becomes possible.

FIGS. 3A and 3B show the results of calculating the COP and the calorific value, respectively, using the low-stage-side evaporation temperature as a parameter. Here, propane and R404 in the deep temperature region
The efficiency was compared with the single-stage circuit using A and the case where the auxiliary capacitor 9 was not provided. As can be seen from FIG. 3 (a), a higher degree of superheating on the higher stage side can be expected to have higher efficiency, and the COP of the cascade circuit is −30 ° C. to −55 ° C. as compared with the COP of propane or the R404A single-stage circuit. Although it is inferior in ℃, there is almost no difference in the region below -60 ℃,
It can be said that it is at a practical level. If the auxiliary capacitor 9 is installed before the low-stage cascade capacitor,
When the superheat degree of the high-stage evaporator is 10 deg, a COP increase of 0.1 to 015 can be expected.

FIGS. 4A and 4B show the calculation results of the COP and the calorific value when ΔT is used as a parameter. FIG.
As is clear from (a), 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 of the cascade system, the same refrigeration circuit as that suitable for the high-stage compressor is used.
It is possible to obtain P. It should be noted that the present invention is not limited to the embodiment, but can be applied to a multiple refrigerating circuit.

[0014]

As described above, according to the present invention,
Since a natural refrigerant is used for the high-stage side and a carbon dioxide gas refrigerant is used for the low-stage side, there is an effect that suppression of high-pressure operation and avoidance of explosion danger can be achieved at the same time. In addition, by installing an auxiliary capacitor before the low-stage cascade capacitor, the coefficient of performance (CO
The effect of improving P) can also be expected.

[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 the relationship between pressure and enthalpy.

3A and 3B are analysis results using a lower-stage evaporation temperature as a parameter, and FIG. 3A is a relationship diagram between a lower-stage evaporation temperature and a COP;
(B) shows the relationship between the lower stage evaporation temperature and the amount of heat

FIG. 4 shows the difference (Δ) between the low-stage condensation temperature and the high-stage evaporation temperature.
T) is an analysis result using the parameter as a parameter.
Relationship between T and COP, (b) Relationship between ΔT and heat

[Explanation of symbols]

 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

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiyuki Ehara 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Masaya Tadano 2-5-2 Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd.

Claims (4)

[Claims] 1. A cascade type refrigeration system, wherein a natural refrigerant is used on a high stage side and a carbon dioxide gas refrigerant is used on a low stage side. 2. A cascade condenser including a high-stage evaporator and a low-stage condenser is commonly used to form a high-stage circulation circuit and a low-stage circulation circuit. The cascade refrigeration apparatus according to claim 1, wherein a system refrigerant is used, and a carbon dioxide gas refrigerant is used as a refrigerant in the low-stage circulation path. 3. The cascade refrigeration system according to claim 2, wherein a hydrocarbon-based refrigerant is used as the refrigerant in the high-stage circulation path. 4. The cascade refrigeration system according to claim 2, wherein an auxiliary condenser for cooling the refrigerant to a predetermined temperature is provided before the low-stage condenser of the cascade condenser.