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 ( 31 a ) 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 ).

1 . A refrigeration system comprising:
 a compressor for compressing refrigerant;   a condenser for cooling the refrigerant discharged from the compressor to condense the refrigerant;   a supercooler, having a primary side through which the refrigerant discharged from the condenser flows and a secondary side through which the refrigerant discharged from the primary side and reduced in pressure by a supercooler pressure reducing element flows, for cooling the refrigerant in the primary side by heat exchange with the refrigerant in the secondary side;   a main cooler for evaporating the refrigerant discharged from the primary side of the supercooler and reduced in pressure by a main cooler pressure reducing element to cool a cooling target; and   a supercooler refrigerant flow rate increasing device for allowing liquid refrigerant of the refrigerant discharged from the primary side of the supercooler to flow into the secondary side of the supercooler at a higher rate than into the main cooler.   
   
   
       2 . A refrigeration system comprising:
 a compressor for compressing refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed;   a condenser for cooling a high-boiling refrigerant component in the refrigerant mixture discharged from the compressor to condense the high-boiling refrigerant component;   multiple stages of gas-liquid separators for separating individual refrigerant components in the refrigerant mixture discharged from the condenser into liquid refrigerant and gas refrigerant in order from higher- to lower-boiling refrigerant components;   multiple stages of cascade heat exchangers for individually cooling the gas refrigerant separated by the associated gas-liquid separator by heat exchange with the liquid refrigerant separated by the associated gas-liquid separator and then reduced in pressure by a pressure reducing element;   a supercooler, having a primary side through which the low-boiling refrigerant component discharged from the final-stage cascade heat exchanger flows and a secondary side through which the low-boiling refrigerant component discharged from the primary side and reduced in pressure by a supercooler pressure reducing element flows, for cooling the low-boiling refrigerant component in the primary side by heat exchange with the low-boiling refrigerant component in the secondary side;   a main cooler for evaporating the low-boiling refrigerant component discharged from the primary side of the supercooler and reduced in pressure by a main cooler pressure reducing element to cool a cooling target down to an ultra-low temperature level; and   a supercooler refrigerant flow rate increasing device for allowing liquid refrigerant of the refrigerant discharged from the primary side of the supercooler to flow into the secondary side of the supercooler at a higher rate than into the main cooler.   
   
   
       3 . The refrigeration system of  claim 1  or  2 , wherein
 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 at the upstream end to the upstream end of 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.   
   
   
       4 . The refrigeration system of  claim 1  or  2 , wherein
 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 at the upstream end to the upstream end of 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.   
   
   
       5 . The refrigeration system of  claim 3 , wherein 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. 
   
   
       6 . A vacuum apparatus configured to freeze moisture in a vacuum chamber by cooling the moisture through the main cooler in the refrigeration system of any one of  claims 1  to  2 . 
   
   
       7 . An ultra-low temperature freezer comprising:
 a compressor for compressing refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed;   a condenser for cooling a high-boiling refrigerant component in the refrigerant mixture discharged from the compressor to liquefy the high-boiling refrigerant component;   a first oil separator for removing, from the refrigerant mixture flowing from the discharge side of the compressor toward the condenser, refrigerator oil mixed in the refrigerant mixture;   multiple stages of gas-liquid separators for separating individual refrigerant components in the refrigerant mixture liquefied by the condenser into liquid refrigerant and gas refrigerant in order from higher- to lower-boiling refrigerant components;   multiple stages of cascade heat exchangers for individually cooling the gas refrigerant separated by the associated gas-liquid separator by heat exchange with the liquid refrigerant separated by the associated gas-liquid separator and reduced in pressure;   a cooler for evaporating the low-boiling refrigerant component discharged from the final-stage cascade heat exchanger of the multiple stages of cascade heat exchangers and reduced in pressure to cool a cooling target down to an ultra-low temperature level; and   a defrosting circuit for supplying the refrigerant mixture discharged from the compressor to the cooler during defrosting of the cooler,   wherein the defrosting circuit is provided with a second oil separator for removing refrigerator oil from the refrigerant mixture.   
   
   
       8 . The ultra-low temperature freezer of  claim 7 , wherein
 the defrosting circuit is provided with a shut-off valve that is opened during defrosting, and   the second oil separator is disposed between the upstream end of the defrosting circuit and the shut-off valve.   
   
   
       9 . The ultra-low temperature freezer of  claim 7  or  8 , wherein the second oil separator is disposed at a location along the defrosting circuit at which the distance to the upstream end of the defrosting circuit is shorter than the distance to the downstream end thereof. 
   
   
       10 . An ultra-low temperature freezer comprising a refrigerant circuit in which are connected:
 a compressor for compressing refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed;   a condenser for cooling a high-boiling refrigerant component in the refrigerant mixture discharged from the compressor to liquefy the high-boiling refrigerant component;   multiple stages of gas-liquid separators for separating individual refrigerant components in the refrigerant mixture liquefied by the condenser into liquid refrigerant and gas refrigerant in order from higher- to lower-boiling refrigerant components;   multiple stages of cascade heat exchangers for individually cooling the gas refrigerant separated by the associated gas-liquid separator by heat exchange with the liquid refrigerant separated by the associated gas-liquid separator and reduced in pressure; and   a cooler for evaporating the low-boiling refrigerant component discharged from the final-stage cascade heat exchanger of the multiple stages of cascade heat exchangers and reduced in pressure to cool a cooling target down to an ultra-low temperature level,   wherein the refrigerant circuit is connected with a plurality of buffer tanks for restraining abnormal increase in the discharge pressure of the compressor.   
   
   
       11 . The ultra-low temperature freezer of  claim 10 , wherein
 the plurality of buffer tanks include at least one first buffer tank and at least one second buffer tank located below the first buffer tank,   the first and second buffer tanks are connected to each other through a communicating passage for providing flow communication of gas refrigerant between the first and second buffer tanks, and   the second buffer tank is connected to one side of the refrigerant circuit toward the discharge part of the compressor and the other side toward the suction part of the compressor.   
   
   
       12 . The ultra-low temperature freezer of  claim 10 , wherein
 the plurality of buffer tanks include at least one first buffer tank and at least one second buffer tank,   the first and second buffer tanks are connected to each other through a communicating passage for providing flow communication of gas refrigerant between the first and second buffer tanks,   the first buffer tank is connected to the side of the refrigerant circuit located toward the discharge part of the compressor, and   the communicating passage is connected partway therethrough to the side of the refrigerant circuit located toward the suction part of the compressor.   
   
   
       13 . The ultra-low temperature freezer of  claim 10 , wherein
 the plurality of buffer tanks include at least one first buffer tank and at least one second buffer tank,   the first and second buffer tanks are connected to each other through a communicating passage for providing flow communication of gas refrigerant between the first and second buffer tanks,   the first buffer tank is connected to the side of the refrigerant circuit located toward the discharge part of the compressor, and   the second buffer tank is connected to the side of the refrigerant circuit located toward the suction part of the compressor.   
   
   
       14 . An ultra-low temperature freezer comprising
 a refrigerant circuit in which are connected:   a compressor for compressing refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed;   a condenser for cooling a high-boiling refrigerant component in the refrigerant mixture discharged from the compressor to liquefy the high-boiling refrigerant component;   multiple stages of gas-liquid separators for separating individual refrigerant components in the refrigerant mixture liquefied by the condenser into liquid refrigerant and gas refrigerant in order from higher- to lower-boiling refrigerant components;   multiple stages of cascade heat exchangers for individually cooling the gas refrigerant separated by the associated gas-liquid separator by heat exchange with the liquid refrigerant separated by the associated gas-liquid separator and reduced in pressure; and   a cooler for evaporating the low-boiling refrigerant component discharged from the final-stage cascade heat exchanger of the multiple stages of cascade heat exchangers and reduced in pressure to cool a cooling target down to an ultra-low temperature level, and   a defrosting circuit for supplying the refrigerant mixture discharged from the compressor to the cooler during defrosting of the cooler, wherein   the downstream end part of the defrosting circuit is branched into a main branch circuit and a sub-branch circuit,   the downstream end of the main branch circuit is connected to one side of the refrigerant circuit toward the entrance of the cooler, and   the downstream end of the sub-branch circuit is connected to the other side of the refrigerant circuit toward the exit of the cooler.   
   
   
       15 . The ultra-low temperature freezer of  claim 14 , wherein the sub-branch circuit is provided with a shut-off valve. 
   
   
       16 . An ultra-low temperature freezer comprising a refrigerant circuit in which are connected:
 a compressor for compressing refrigerant mixture in which plural kinds of refrigerants having different boiling points are mixed;   a condenser for cooling a high-boiling refrigerant component in the refrigerant mixture discharged from the compressor to liquefy the high-boiling refrigerant component;   multiple stages of gas-liquid separators for separating individual refrigerant components in the refrigerant mixture liquefied by the condenser into liquid refrigerant and gas refrigerant in order from higher- to lower-boiling refrigerant components;   multiple stages of cascade heat exchangers for individually cooling the gas refrigerant separated by the associated gas-liquid separator by heat exchange with the liquid refrigerant separated by the associated gas-liquid separator and reduced in pressure;   a pressure reducing element for reducing the pressure of the low-boiling refrigerant component discharged from the final-stage cascade heat exchanger of the multiple stages of cascade heat exchangers; and   a cooler for evaporating the low-boiling refrigerant component reduced in pressure by the pressure reducing element to cool a cooling target down to an ultra-low temperature level, wherein   part of the refrigerant circuit for supplying refrigerant from the final-stage cascade heat exchanger to the cooler comprises a plurality of branch circuits connected in parallel with each other,   the pressure reducing element comprises a plurality of branch pressure reducing elements series-connected into the plurality of branch circuits, respectively, and   at least one of the plurality of branch circuits is provided with a selector for turning the at least one branch circuit on to pass the refrigerant therethrough.   
   
   
       17 . The ultra-low temperature freezer of  claim 16 , wherein the selector comprises a shut-off valve disposed in at least one of the plurality of branch circuits. 
   
   
       18 . The ultra-low temperature freezer of  claim 16  or  17 , wherein the plurality of branch pressure reducing elements have different pressure reduction capabilities. 
   
   
       19 . The ultra-low temperature freezer of any one of  claims 16  or  17 , wherein the branch pressure reducing element comprises a capillary tube. 
   
   
       20 . A vacuum apparatus configured to freeze moisture in a vacuum chamber by cooling the moisture with the cooler in the ultra-low temperature freezer of any one of  claims 7 ,  10  and  14 .