EP1843109A2

EP1843109A2 - Cooling System

Info

Publication number: EP1843109A2
Application number: EP07104133A
Authority: EP
Inventors: Yukio C/o Sanden Corporation Yamaguchi
Original assignee: Sanden Corp
Current assignee: Sanden Corp
Priority date: 2006-04-03
Filing date: 2007-03-14
Publication date: 2007-10-10
Also published as: JP2007278541A; EP1843109A3

Abstract

The invention provides a cooling system capable of enhancing refrigeration efficiency even when using a carbon dioxide refrigerant. Namely, when an outer surface area of a high-pressure pipe is set to be in a range from 10% to 25% inclusive of a total inner surface area of a heat exchanging pipe of the evaporator, the coefficient of performance can be made large and the refrigeration efficiency can be enhanced.

Description

The present invention relates to a cooling system used in an automatic vending machine, an air conditioner, a refrigerated and cold-storage showcase and the like.
Conventionally, as a cooling system of this kind, there is known the one including a refrigeration circuit constituted of a compressor, a radiator, an expansion mechanism and an evaporator, and circulating a refrigerant through the compressor, the radiator, the expansion mechanism, the evaporator and the compressor in this sequence. In the cooling system, the refrigerant which is compressed in the compressor to be at high temperature and high pressure releases heat in the radiator, and thereafter, is supplied to the expansion mechanism through a high-pressure pipe. Then, the refrigerant expanded to be at low pressure in the expansion mechanism flows into the evaporator, and evaporates by absorbing the ambient heat. Thereafter, the refrigerant is supplied to the compressor through the low-pressure pipe and is compressed again.
Conventionally, the refrigerant generally used in cooling systems is fluorocarbon, but now it becomes the problem that fluorocarbon destroys the ozone layer surrounding the earth. Therefore, in recent years, the cooling system using carbon dioxide that is natural refrigerant as a refrigerant in place of fluorocarbon has been known. In the cooling system using carbon dioxide as a refrigerant, the refrigerant at the high pressure side is in a supercritical state.
In order to enhance the refrigerating capacity, the cooling system using carbon dioxide as a refrigerant adopts the method for radiating heat of the refrigerant flowing in the high-pressure pipe by exchanging heat of the refrigerants flowing in respective pipes with each other by welding the outer peripheral side surface of the high-pressure pipe and the outer peripheral side surface of the low-pressure pipe.
However, in the above described cooling system, heat exchange is performed at only a part of the outer periphery of each of the pipes, and the heat exchange area is small. Therefore, heat exchange rate of the refrigerant flowing in each of the pipes is low, and it is difficult to enhance refrigeration efficiency especially in the cooling system using carbon dioxide as the refrigerant.
An object of the present invention is to provide a cooling system capable of enhancing refrigeration efficiency even when using a carbon dioxide as the refrigerant.
In order to attain the above described object, the present invention includes a refrigeration circuit which has a compressor, a radiator an expansion mechanism and an evaporator, and in which carbon dioxide circulates as a refrigerant, a high-pressure pipe connecting the radiator and the expansion mechanism to allow a high-pressure refrigerant flowing out of the radiator to flow therethrough, a low-pressure pipe connecting the evaporator and the compressor to allow a low-pressure refrigerant flowing out of the evaporator to flow therethrough, and a heat exchanging part for performing heat exchange of the refrigerant flowing through an inside of the high-pressure pipe and the refrigerant flowing through an inside of the low-pressure pipe by disposing the high-pressure pipe in the low-pressure pipe, and an outer surface area of the high-pressure pipe in the heat exchange part is set to be in a range from 10% to 25% inclusive of an inner surface area of a heat exchanging pipe of the evaporator.
As a result, when the outer surface area of the high-pressure pipe is set to be in the range from 10% to 25% inclusive of the inner surface area of the heat exchanging pipe constituting the evaporator, the coefficient of performance is larger and the refrigeration efficiency is higher than when the outer surface area of the high-pressure pipe is less than 10% of the inner surface area of the heat exchanging pipe and when the outer surface area of the high-pressure pipe is larger than 25% of the inner surface area of the heat exchanging pipe. Accordingly, if the outer surface area of the high-pressure pipe is set to be in the range from 10% to 25% inclusive of the inner surface area of the heat exchanging pipe, the refrigeration efficiency of the cooling system can be enhanced, and it is extremely advantageous when the cooling system is used in an automatic vending machine, for example.
These and other objects, features and advantages of the present invention will become apparent by the following description and the accompanying drawings.

In the Drawings;

FIG. 1 is a schematic diagram of a cooling system according to a first embodiment of the present invention;
FIG. 2 is a plane view of an evaporator according to the first embodiment;
FIG. 3 is a sectional view in the A-A' direction of a heat exchanging pipe shown in FIG. 2;
FIG. 4 is a side sectional view of a heat exchanger constituted of a high-pressure pipe and a low-pressure pipe shown in FIG. 1;
FIG. 5 is a sectional view in the B-B' direction of the high-pressure pipe and the low-pressure pipe shown in FIG. 4;
FIG. 6 is a diagram showing the relationship of the ratio of the outer surface area of the high-pressure pipe to the inner surface area of the heat exchanging pipe, and the coefficient of performance of the cooling system;
FIG. 7 is a side view of a heat exchanger constituted of the high-pressure pipe and the low-pressure pipe of a cooling system according to a second embodiment of the present invention;
FIG. 8 is a schematic diagram showing a modified example of the cooling system according to the present invention; and
FIG. 9 is a schematic diagram showing a modified example of the heat exchanger according to the present invention.

Detailed description of the invention

FIGS. 1 to 6 show a cooling system according to a first embodiment of the present invention.
The cooling system shown in FIG. 1 includes a refrigeration circuit constituted of a compressor 10, a radiator 11, an expansion valve 12 as an expansion mechanism and an evaporator 13. The refrigerant used in this cooling system is carbon dioxide as a natural refrigerant.
The radiator 11 is an air cooling type heat exchanger for allowing air and the refrigerant to exchange heat.
The evaporator 13 includes, as shown in FIGS. 1 and 2, a heat exchanging pipe 14 which linearly extends in the direction perpendicular to the flowing direction of air to be cooled and is provided in a meandering state, and a plurality of fins 15 which are equidistantly disposed in the refrigerant flowing direction of the heat exchanging pipe 14 to increase the surface area of the heat exchanging pipe 14. Heat exchange is practically performed in the width L of the heat exchanging pipe 14 where the fins 15 are disposed. In the embodiment, the heat exchanging pipe 14 in which heat exchange is practically performed is constituted of a first heat exchanging pipe 14a, a second heat exchanging pipe 14b, a third heat exchanging pipe 14c, a fourth heat exchanging pipe 14d, a fifth heat exchanging pipe 14e and a sixth heat exchanging pipe 14f.
The cooling system can circulate the refrigerant through the compressor 10, the radiator 11, the expansion valve 12, the evaporator 13 and the compressor 10 in this sequence (see the solid line arrow shown in FIG. 1). At this time, the refrigerant flows through the compressor 10, the radiator 11 and the expansion valve 12 under high pressure (hereinafter, called a high-pressure side), and flows through the expansion valve 12, the evaporator 13 and the compressor 10 under low pressure (hereinafter, called a low-pressure side).
The radiator 11 and the expansion valve 12 provided at the high-pressure side of the cooling system are connected by a high-pressure pipe 20. The evaporator 13 and the compressor 10 provided at the low-pressure side of the cooling system are connected by a low-pressure pipe 21. The cooling system includes a heat exchanger 22 (see the dashed line portion shown in FIG. 1) as a heat exchanging part which performs heat exchange of the refrigerant flowing in the high-pressure pipe 20 and the refrigerant flowing in the low-pressure pipe 21. The high-pressure pipe 20, the low-pressure pipe 21 and the heat exchanger 22 will be described in detail by using FIGS. 4 and 5.
The high-pressure pipe 20 connects the radiator 11 and the expansion valve 12, and allows the refrigerant at high pressure flowing out of the radiator 11 to pass through it (see the hollow arrows shown in FIG. 4).
The low-pressure pipe 21 connects the evaporator 13 and the compressor 10, and allows the refrigerant at low pressure flowing out of the evaporator 13 to pass through it (see the solid line arrows shown in FIG. 5).
The heat exchanger 22 is provided by disposing a part of the high-pressure pipe 20 inside a part of the low-pressure pipe 21 by using a pair of connecting members 23. The heat exchanger 22 is provided so that the direction in which the refrigerant in the low-pressure pipe 21 flows and the direction in which the refrigerant in the high-pressure pipe 20 flows are opposed to each other, so that the refrigerant flowing in the low-pressure pipe 21 and the refrigerant flowing in the high-pressure pipe 20 exchange heat with each other.
Here, as shown in FIGS. 2 and 3, the inside diameter of the heat exchanging pipe 14 is d, and the pipe length of each of the first to the sixth heat exchanging pipes 14a, 14b, 14c, 14d, 14e and 14f of the heat exchanging pipe 14 in which heat exchange is practically performed is L. Thereby, the total inner surface area S1 of the heat exchanging pipe 14 can be regarded as 6πdL.
As shown in FIGS. 4 and 5, the outside diameter of the high-pressure pipe 20 in the heat exchanger 22 is D, and the pipe length of the heat exchanger 22 is L'. Thereby, the outer surface area S2 of the high-pressure pipe 20 in the heat exchanger 22 can be regarded as πDL'.
The ratio X of the outer surface area S2 of the high-pressure pipe 20 to the total inner surface area S1 of the heat exchanging pipe 14 thus expressed is calculated, and the relationship between the ratio X and the coefficient of performance (COP) of the cooling system will be described with reference to FIG. 6. The relationship between the ratio X and the coefficient of performance of the cooling system is the measurement result of the experiment in three kinds of refrigerant charge amounts.
As shown in FIG. 6, it is found out that when the outer surface area S2 of the high-pressure pipe 20 is less than 10% of the total inner surface area S1 of the heat exchanging pipe 14 of the evaporator 13, the coefficient of performance of the cooling system becomes small and the refrigeration efficiency reduces. It is also found out that when the outer surface area 32 of the high-pressure pipe 20 is larger than 25% of the total inner surface area S1 of the heat exchanging pipe 14, the coefficient of performance of the cooling system also becomes small and the refrigeration efficiency also reduces. Namely, it is found out that when the outer surface area S2 of the high-pressure pipe 20 is set to be in the range from 10% to 25% inclusive of the total inner surface area S1 of the heat exchanging pipe 14, the coefficient of performance becomes larger and the refrigeration efficiency becomes higher than when the outer surface area S2 of the high-pressure pipe 20 is smaller than 10% and larger than 25% of the total inner surface area S1 of the heat exchanging pipe 14.
Next, the operation of the cooling system constituted as above will be described.
The refrigerant of the cooling system circulates through compressor 10, the radiator 11, the expansion valve 12, the evaporator 13 and the compressor 10 in this sequence (see the solid line arrows in FIG. 1). At this time, in the heat exchanger 22, the refrigerant flowing in the low-pressure pipe 21 (see the solid line arrows shown in FIG. 4) and the refrigerant flowing in the high-pressure pipe 20 (see the hollow arrows shown in FIG. 4) exchange heat with each other. Namely, the refrigerant flowing out of the radiator 11 releases heat in the heat exchanger 22, and thereafter, is supplied to the expansion valve 12. Then, the refrigerant flowing out of the expansion valve 12 flows into the evaporator 13, exchanges heat with air via the heat exchanging pipe 14 and the fins 15 and evaporates. After the refrigerant absorbs heat in the heat exchanger 22, it is returned to the compressor 10.
As this, according to the cooling system of the embodiment, when the outer surface area S2 of the high-pressure pipe 20 is set to be in the range from 10% to 25% inclusive of the total inner surface area S1 of the heat exchanging pipe 14 of the evaporator 13, the coefficient of performance becomes large and the refrigeration efficiency becomes high, and therefore, the amount of energy consumed can be reduced. For example, by using the cooling system in an automatic vending machine, the automatic vending machine becomes extremely advantageous with regard to energy conservation.
Further, according to the cooling system of the embodiment, the heat exchanger 22 is adapted so that the direction in which the refrigerant in the low-pressure pipe 21 flows and the direction in which the refrigerant in the high-pressure pipe 20 flows are opposed to each other, and therefore, heat exchange of the refrigerant flowing in the low-pressure pipe 21 and the refrigerant flowing in the high-pressure pipe 20 can be performed efficiently. In addition, the heat exchanger 22 can be of the structure corresponding to the flow of the refrigerant in the cooling system, and therefore, space of the installation place of the heat exchanger 22 can be saved.
Further, according to the cooling system of the embodiment, the refrigerant before being supplied to the expansion valve 12 releases heat in the heat exchanger 22. Therefore, the enthalpy difference of the refrigerant increases, and the refrigeration capacity is increased.
FIG. 7 is a side view of a heat exchanger constituted of the high-pressure pipe and the low-pressure pipe of the cooling system according to a second embodiment of the present invention. The same components as in the cooling system shown in FIGS. 1 to 6 are expressed by the same reference numerals, and the explanation of them will be omitted.
A heat exchanger 32 shown in FIG. 7 differs from the heat exchanger 22 shown in FIG. 4 in the respect that the high-pressure pipe 20 and the low-pressure pipe 21 constituting the heat exchanger 32 are each formed into a spiral shape.
The heat exchanger 32 is provided by disposing a part of the high-pressure pipe 20 inside a part of the low-pressure pipe 21 by using a pair of connecting members 23. In the heat exchanger 32, the high-pressure pipe 20 and the low-pressure pipe 21 constituting the heat exchanger 32 are each formed into the spiral shape. The heat exchanger 32 performs heat exchange of the refrigerant flowing in the low-pressure pipe 21 (see the solid line arrows shown in FIG. 7) and the refrigerant flowing in the high-pressure pipe 20 (see the hollow arrows shown in FIG. 7). Further, the heat exchanger 32 allows the refrigerant in the high-pressure pipe 20 to flow upward from below, and allows the refrigerant in the low-pressure pipe 21 to flow downward from above.
The operation of the cooling system including the heat exchanger 32 constituted as above is the same as the above described first embodiment, and therefore, the explanation of it will be omitted.
As above, according to the cooling system of the embodiment, by forming the heat exchanger 32 in the spiral shape, the space of the installation place of the heat exchanger 32 can be further saved.
Further, the heat exchanger 32 can prevent oil accumulation from occurring in each of the pipes 20 and 21 by allowing the refrigerant in the high-pressure pipe 20 to flow upward from below, and allowing the refrigerant in the low-pressure pipe 21 to flow downward from above. Thereby, pressure loss can be prevented from occurring in the cooling system, reduction in the refrigeration efficiency of the cooling system can be suppressed. The other operation and effect are the same as in the above described first embodiment.
In the above described first and second embodiments the heat exchanging pipe 14 in which heat exchange is practically performed is constituted of six pipes in total, that is, the first to the sixth heat exchanging pipes 14a to 14f, but the heat exchanging pipe is not limited to this. The number of pipes of the heat exchanging pipe 14 in which heat exchange is practically performed can be increased and decreased in accordance with the desired evaporation efficiency of the evaporator 13, for example.
In the above described first and second embodiments, the cooling system includes only one evaporator 13, but the number of evaporators 13 is not limited to this. The cooling system may include a plurality of evaporators 13 as in the cooling system shown in FIG. 8, for example. In this case, a plurality of evaporators 13 may be connected via the radiator 11 and an electromagnetic valve 16. Thereby, desired evaporation efficiency of the cooling system can be obtained by controlling the electromagnetic valve 16.
Further, in the above described second embodiment, the heat exchanger 32 is formed into a spiral shape, but the heat exchanger 32 is not limited to this. For example, it may be formed into a circinate shape as a heat exchanger 42 shown in FIG. 9. In this case, the heat exchanger 42 is adapted to allow the refrigerant in the high-pressure pipe 20 to flow to the center side from the outer side and allow the refrigerant in the low-pressure pipe 21 to flow to the outer side from the center side. As a result, by forming the heat exchanger 42 in the circinate shape, the space for the installation place of the heat exchanger 42 can be further saved. The other operation and effect are the same as in the above descried first and second embodiments.
The embodiments described in the specification are only illustrative and not restrictive. The scope of the invention is shown by the accompanying claims, and all the modified examples included in the meanings of these claims are included in the present invention.

Claims

A cooling system, comprising:
a refrigeration circuit which has a compressor (10), a radiator (11), an expansion mechanism (12) and an evaporator (13), and in which carbon dioxide circulates as a refrigerant;

a high-pressure pipe (20) connecting the radiator (11) and the expansion mechanism (12) to allow a high-pressure refrigerant flowing out of the radiator (11) to flow therethrough;

a low-pressure pipe (21) connecting the evaporator (13) and the compressor (10) to allow a low-pressure refrigerant flowing out of the evaporator (13) to flow therethrough; and

a heat exchanging part (22, 32, 42) for performing heat exchange of the refrigerant flowing through an inside of the high-pressure pipe (20) and the refrigerant flowing through an inside of the low-pressure pipe (21) by disposing the high-pressure pipe (20) in the low-pressure pipe (21),
wherein an outer surface area of the high-pressure pipe (20) in the heat exchange part (22, 32, 42) is set to be in a range from 10% to 25% inclusive of an inner surface area of a heat exchanging pipe (14) of the evaporator (13).
The cooling system according to claim 1, wherein:
in said heat exchanging part (22, 32, 42), a direction in which the refrigerant in the high-pressure pipe (20) flows is in a direction opposed to a direction in which the refrigerant in the low-pressure pipe (21) flows.
The cooling system according to claim 2, wherein:
said heat exchanging part (32) is formed into a spiral shape.
The cooling system according to any one of claims 1 to 3, wherein:
in said heat exchanging part (22, 23), the refrigerant in the high-pressure pipe (20) flows toward an upper portion from a lower portion, and the refrigerant in the low-pressure pipe (21) flows toward the lower portion from the upper portion.
The cooling system according to claim 2, wherein:
said heat exchanging part (42) is formed into a circinate shape.
The cooling system according to claim 5, wherein:
in said heat exchanging part (42), the refrigerant in the high-pressure pipe (20) flows toward a center portion side from an outer peripheral portion side, and the refrigerant in the low-pressure pipe (21) flows toward the outer peripheral portion side from the center portion side.