1. Field of the Invention
The present invention relates to a cooling system for cooling a substance to be cooled.
2. Description of Related Art
Japanese Examined Patent Publication (KOKOKU) No. 45-27,634 discloses a conventional cooling system which is constructed as illustrated in FIG. 5. As illustrated in FIG. 5, this conventional cooling system comprises a cold gas refrigerator 101 which operates under reverse Stirling cycle, and a cooling circuit 120 for delivering cold to a substance 110 to be cooled.
The cold gas refrigerator (hereinafter simply referred to as "refrigerator") 101 includes a cylinder 100, a piston 102 which reciprocates in the cylinder 100, a displacer 103 which reciprocates with a predetermined phase difference with respect to the piston 102, a chiller 106 which communicates with a compression chamber 104 disposed between the piston 102 and the displacer 103, a freezer 108 which is disposed in an expansion chamber 105 placed between the displacer 103 and a top end of the cylinder 101, and a regenerator 107 which is disposed between the chiller 106 and the expansion chamber 105.
The cooling circuit 120 includes a compressor 121, a piping 124, and a counterflow heat exchanger 123 which is disposed between the piping 124 and the compressor 121. The piping 124 includes a plurality of heat exchangers 125 for conducting cold, and a plurality of heat exchangers 126 for cooling a substance 110 to be cooled. The heat exchangers 125 are thermally brought into contact with the freezer 108. The heat exchangers 125 and the heat exchangers 126 are disposed alternately in series.
In the thus constructed conventional cooling system, the piston 102 compresses a working medium to produce heat in the compression chamber 104 of the refrigerator 101 (i.e., isothermal compression). Then, the displacer 103 moves toward the piston 102 to cool and pass the working medium through the regenerator 107 (i.e., constant-volume cooling). Further, the piston 102 retracts to produce cold in the expansion chamber 105 (i.e., isothermal expansion), and the cold is absorbed by the other working medium which flows in the cold-conducting heat exchanger 125 being thermally brought into contact with the freezer 108. Furthermore, the displacer 103 moves to its top dead center, and thereby the working medium cools the regenerator 107 and returns to the compression chamber 104 (i.e., constant-volume heating).
The other working medium flows in the cooling circuit 120. When it flows in the cold-conducting heat exchanger 125, its heat is absorbed, and cold thus produced is conducted to the heat exchanger 126 for cooling. Accordingly, the substance 110 to be cooled is cooled. The counterflow heat exchanger 123 cools the high-pressure working medium, which is delivered from the compressor 121, by means of the low-pressure working medium which returns to the compressor 121.
The thus constructed cooling system can employ a helium gas as the working media, and can be applied to home-use refrigerators, air conditioners, etc. When its refrigerator employs a multi-staged expansion arrangement, and when its cooling circuit utilizes a Joule-Thomson (hereinafter referred to as "J-T") circuit, it is possible to attain a liquefied helium temperature as low as 4.2K, and to cool superconducting magnets.
In the counterflow heat exchanger 123 of the thus constructed cooling system, its low-pressure-side passage 123b is connected to an inlet port of the compressor 121, and its high-pressure-side passage 123a is connected to an outlet port of the compressor 121. The flow of the other working medium flowing in the low-pressure-side passage 123b is equal to the flow of the other working medium flowing in the high-pressure-side passage 123a. Accordingly, in the counterflow heat exchanger 123, the heat exchange is carried out in an averaged manner.
If the flow in the low-pressure-side passage 123b could be set larger than that of the flow in the high-pressure-side passage 123a, the other working medium of high-temperature flowing in the high-pressure-side passage 123a could be cooled by the other working medium of low-temperature flowing in the low-pressure-side passage 123b with enhanced cooling efficiency. As a result, it is assumed that the temperature of the other working medium of high-pressure prior to flowing into the cold-conducting heat exchanger 125 could be reduced considerably, and that the cold-conducting heat exchanger 125 could be enhanced accordingly in terms of Carnot efficiency.
Hence, in order to set the flow in the low-pressure-side passage 123b larger than the flow in the high-pressure-side passage 123a, one may think of branching part of the other working medium flowing into the high-pressure-side passage 123a.
However, the flow in the low-pressure-side passage 123b should eventually be identical with the flow in the high-pressure-side passage 123a. In other words, the flow should be equal on the outlet-port side and the inlet-port side of the compressor 121. Consequently, it is needed to join the branched flow with the working medium which has been flowed in the high-pressure-side passage 123a downstream with respect to the counterflow heat exchanger 123. If such the case, the cooling efficiency in the cold-conducting heat exchangers 125 is degraded sharply, because the branched working medium is not cooled by the counterflow heat exchanger 123. Accordingly, in spite of the enhanced cooling efficiency in the counterflow heat exchanger 123, there arises a problem in that the substance 110 to be cooled cannot be cooled with improved cooling capability.