Ultra-low temperature freezer, refrigeration system and vacuum apparatus

Abstract

In an ultra-low temperature freezer (R) using refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed, in order to ensure the flow rate of liquid refrigerant into a supercooler (31) and enhance the cooling efficiency of a cryocoil (32), the ultra-low temperature freezer (R) comprises: a main refrigerant circuit (38) provided with the cryocoil (32) and a capillary tube (29); and a sub refrigerant circuit (39) that is connected at the upstream end to the upstream end of the main refrigerant circuit (38) to branch off therefrom and provided with a capillary tube (28), and the ultra-low temperature freezer (R) is configured so that the sub refrigerant circuit (39) is lower in height than the main refrigerant circuit (38). Thus, gas-liquid mixture refrigerant discharged from the primary side (31a) of the supercooler (31) flows into the sub refrigerant circuit (39) at a higher rate than into the main refrigerant circuit (38) and, in turn, liquid refrigerant flows more into the sub refrigerant circuit (39) than into the main refrigerant circuit (38).

Description

TECHNICAL FIELD[0001]This invention relates to an ultra-low temperature freezer for creating a cold environment at an ultra-low temperature level, a refrigeration system for the same purpose and a vacuum apparatus provided with one of them.BACKGROUND ART[0002]Conventionally known refrigeration systems for creating a cold environment at an ultra-low temperature level of −100° C. or below include mixed refrigerant type ultra-low temperature freezers in which a refrigerant circuit is charged with a non-azeotropic refrigerant mixture obtained by mixing plural kinds of refrigerants having different boiling temperatures, as disclosed, for example, in Patent Documents 1, 2 and 3. An ultra-low temperature freezer of such kind is placed in, for example, a vacuum chamber of a vacuum deposition apparatus for use in manufacturing substrates (wafers), and used to raise the vacuum level in the vacuum chamber by trapping moisture or the like in it by freezing.[0003]The refrigerant circuit of the a...

AI Technical Summary

Benefits of technology

[0076]As described so far, the first or second aspect of the invention is directed to a refrigeration system comprising a main cooler for cooling a cooling target and a supercooler for cooling refrigerant in its primary side with refrigerant in its secondary side, wherein the refrigeration system further comprises a supercooler refrigerant flow rate increasing device for allowing liquid refrigerant to flow into the secondary side of the supercooler at a higher rate than into the main cooler. Therefore, sufficient cooling of gas refrigerant in the primary side of the supercooler can be ensured to enhance the cooling efficiency of the main cooler. This provides stable cooling of the cooling target and shortens the cool-down time taken to cool the cooling target down to an ultra-low temperature level.

[0077]In the third aspect of the invention, the refrigeration system further comprises: a main refrigerant circuit provided with the main cooler and the main cooler pressure reducing element; and a sub refrigerant circuit that is connected to the main refrigerant circuit to branch off therefrom and provided with the supercooler pressure reducing element, and the supercooler refrigerant flow rate increasing device is configured so that the minimum cross sectional area of the sub refrigerant circuit is larger than the maximum cross sectional area of the main refrigerant circuit. Thus, when the refrigerant discharged from the primary side of the supercooler is distributed into the main and sub refrigerant circuits, gas-liquid mixture refrigerant can flow into the sub refrigerant circuit at a higher rate than into the main refrigerant circuit, and, in turn, liquid refrigerant can flow into the sub refrigerant circuit at a higher rate than into the main refrigerant circuit. In this manner, the supercooler refrigerant flow rate increasing device can be achieved.

[0078]In the fourth aspect of the invention, the refrigeration system further comprises: a main refrigerant circuit provided with the main cooler and the main cooler pressure reducing element; and a sub refrigerant circuit that is connected to the main refrigerant circuit to branch off therefrom and provided with the supercooler pressure reducing element, and the supercooler refrigerant flow rate increasing device is configured so that the maximum height of the sub refrigerant circuit at the bifurcation of the main and sub refrigerant circuits is lower than the minimum height of the main refrigerant circuit at the bifurcation. Thus, when the refrigerant discharged from the primary side of the supercooler is distributed into the main and sub refrigerant circuits, liquid refrigerant of the gas-liquid mixture refrigerant can flow into the sub refrigerant circuit of relatively small height, and, in turn, liquid refrigerant can flow into the sub refrigerant circuit at a higher rate than into the main refrigerant circuit. Therefore, the supercooler refrigerant flow rate increasing device can be achieved with a simple structure.

[0079]According to the fifth aspect of the invention, since in the refrigeration system of the third aspect the maximum height of the sub refrigerant circuit at the bifurcation of the main and sub refrigerant circuits is lower than the minimum height of the main refrigerant circuit at the bifurcation, the behaviors and effects of the third and fourth aspects can synergistically act to further enhance the cooling efficiency of the main cooler.

[0080]According to the sixth aspect of the invention, since moisture in a vacuum chamber of a vacuum apparatus is frozen by cooling it using the main cooler of the refrigeration system, this provides a stable vacuum condition in the vacuum chamber and shortened cool-down time, and shortened exhaust time and in turn enhanced production efficiency.

[0081]In the seventh aspect of the invention, an oil separator for removing refrigerator oil from the refrigerant mixture is disposed in the defrosting circuit of the ultra-low temperature freezer. Thus, it can be prevented that, during defrosting, the refrigerator oil in the refrigerant mixture is supplied from the defrosting circuit to the cooler to solidify in the cooler, and an increase in pressure loss that would be caused when a plurality of oil separators were disposed in series between the compressor and the condenser can be prevented. This provides enhanced cooling efficiency while ensuring good circulation of the refrigerant mixture.

Problems solved by technology

The above conventional refrigeration systems, however, have problems described below.

However, the refrigerant passing through the bifurcation of the main and sub refrigerant circuits into the main cooler and the secondary side of the supercooler is not fully composed of liquid refrigerant but is supplied to both the coolers as gas-liquid mixture refrigerant partly containing gas refrigerant.

Therefore, even if the system is configured so that refrigerant flowing through the main cooler is equal in flow rate to refrigerant flowing through the supercooler, if the flow rate of liquid refrigerant into the secondary side of the supercooler is low, this provides a shortage of cooling of gas refrigerant in the primary side thereof.

The flow rate of liquid refrigerant obtained by gas refrigerant liquefaction of the supercooler is correspondingly reduced, which invites deteriorated cooling efficiency of the main cooler.

As a result, in the case of load variations of the cooling target to be cooled by the main cooler, there arises a problem of impossibility to stably cool the cooling target against such load variations or a problem of extended cool-down time taken for the main cooler to cool down the cooling target from normal to ultra-low temperature level.

(2) Further, when the normal operation of the freezer is halted and a defrosting operation is performed to supply the discharge gas from the compressor to the cooler through the defrosting circuit and thereby defrost the cooler, if refrigerator oil has failed to be completely removed by the oil separator and remains in it at the start of the defrosting operation, it may flow through the defrosting circuit and may be supplied to the cooler still at an ultra-low temperature level, which causes a problem that the refrigerator oil solidifies in the cooler.

Images