Freezers with cascade refrigeration systems using parallel expansion devices for adjustable expansion

Abstract

A cascade refrigeration system having a first refrigeration stage that defines a first fluid circuit and includes a first expansion device and a second refrigeration stage that defines a second fluid circuit, fluidically isolated from the first fluid circuit, that includes a second expansion device. The second expansion device includes a first capillary tube and a second capillary tube in parallel flow arrangement, and a second stage valve in fluid communication with the second capillary tube for selectively controlling flow of the second refrigerant through the second capillary tube in response to at least one operating condition of the refrigeration system without interrupting flow of the second refrigerant through the first capillary tube. The refrigeration system further includes at least one interstage heat exchanger in heat transferring communication with the first and second fluid circuits to exchange heat between the first and second refrigerants.

What is claimed is: 
     
         1 . A refrigeration system, comprising:
 a first refrigeration stage defining a first fluid circuit for circulating a first refrigerant, the first refrigeration stage having:
 a first condenser; 
 a first compressor; and 
 a first expansion device in fluid communication with the first fluid circuit; 
   a second refrigeration stage defining a second fluid circuit that is fluidically isolated from the first fluid circuit for circulating a second refrigerant, the second refrigeration stage having:
 a second condenser; 
 a second compressor; and 
 a second expansion device in fluid communication with the second fluid circuit, the second expansion device comprising:
 a first capillary tube and a second capillary tube in parallel flow arrangement; and 
 a second stage valve in fluid communication with the second capillary tube for selectively controlling flow of the second refrigerant through the second capillary tube in response to at least one operating condition of the refrigeration system without interrupting flow of the second refrigerant through the first capillary tube; and 
 at least one interstage heat exchanger in heat transferring communication with the first and second fluid circuits to exchange heat between the first and second refrigerants, 
 
   wherein the first and second refrigeration stages are configured in a cascade cooling arrangement.   
     
     
         2 . The refrigeration system of  claim 1 , wherein the first fluid circuit further comprises:
 a first fluid line in fluid communication with an outlet of the first condenser and a first inlet of the at least one interstage heat exchanger, the first fluid line including the first expansion device;   a first suction line in fluid communication with a first outlet of the at least one interstage heat exchanger and an inlet of the first compressor; and   a first heat exchanger defined by a portion of the first fluid line or a portion of the first expansion device being in heat transferring communication with a portion of the first suction line to thereby exchange heat between the first refrigerant flowing through the first fluid line and the first refrigerant flowing through the first suction line.   
     
     
         3 . The refrigeration system of  claim 1 , wherein the second fluid circuit further comprises:
 a second fluid line in fluid communication with a second outlet of the at least one interstage heat exchanger and an inlet of the evaporator, the second fluid line including the second expansion device;   a second suction line in fluid communication with an outlet of the evaporator and an inlet of the second compressor; and   a second heat exchanger defined by a portion of the second fluid line or a portion of the second expansion device being in heat transferring communication with a portion of second suction line to thereby exchange heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.   
     
     
         4 . The refrigeration system of  claim 2 , wherein the second fluid circuit further comprises:
 a second fluid line in fluid communication with a second outlet of the at least one interstage heat exchanger and an inlet of the evaporator, the second fluid line including the second expansion device;   a second suction line in fluid communication with an outlet of the evaporator and an inlet of the second compressor; and   a second heat exchanger defined by a portion of the second fluid line or a portion of the second expansion device being in heat transferring communication with a portion of second suction line to thereby exchange heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.   
     
     
         5 . The refrigeration system of  claim 1 , wherein the first expansion device comprises an electronic expansion valve. 
     
     
         6 . The refrigeration system of  claim 1 , wherein the second stage valve comprises a solenoid valve. 
     
     
         7 . The refrigeration system of  claim 1 , wherein the second stage valve comprises an electronic expansion valve. 
     
     
         8 . The refrigeration system of  claim 1 , wherein the first expansion device further comprises:
 a third capillary tube and a fourth capillary tube in parallel flow arrangement; and   a first stage valve for selectively controlling flow of the first refrigerant through the fourth capillary tube in response to at least one operating condition of the refrigeration system without interrupting flow of the first refrigerant through the third capillary tube.   
     
     
         9 . The refrigeration system of  claim 8 , wherein the first fluid circuit further comprises:
 a first fluid line in fluid communication with an outlet of the first condenser and a first inlet of the at least one interstage heat exchanger, the first fluid line including the first expansion device;   a first suction line in fluid communication with a first outlet of the at least one interstage heat exchanger and an inlet of the first compressor; and   a first heat exchanger defined by a portion of the first suction line being in heat transferring communication with a portion of the first fluid line or a portion of the first expansion device to thereby exchange heat between the first refrigerant flowing through the first fluid line and the first refrigerant flowing through the first suction line.   
     
     
         10 . The refrigeration system of  claim 9 , wherein the second fluid circuit further comprises:
 a second fluid line in fluid communication with a second outlet of the at least one interstage heat exchanger and an inlet of the evaporator, the second fluid line including the second expansion device;   a second suction line in fluid communication with an outlet of the evaporator and an inlet of the second compressor; and   a second heat exchanger defined by a portion of the second fluid line or a portion of the second expansion device being in heat transferring communication with a portion of second suction line to thereby exchange heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.   
     
     
         11 . The refrigeration system of  claim 8 , wherein the first stage valve is a solenoid valve. 
     
     
         12 . The refrigeration system of  claim 8 , wherein the first stage valve is an electronic expansion valve. 
     
     
         13 . The refrigeration system of  claim 8 , wherein the second stage valve is an electronic expansion valve. 
     
     
         14 . The refrigeration system of  claim 8 , wherein the second stage valve comprises a solenoid valve. 
     
     
         15 . The refrigeration system of  claim 1 , wherein the refrigeration system is associated with a cabinet having an interior to be cooled, and the first and second refrigeration stages are operated to cool the cabinet to a temperature setpoint ranging between −20° C. and −90° C. 
     
     
         16 . A freezer, comprising:
 a cabinet having a cabinet interior and a door providing access into the cabinet interior;   a cascade refrigeration system, which comprises:
 a first refrigeration stage defining a first fluid circuit for circulating a first refrigerant, the first refrigeration stage having:
 a first condenser; 
 a first compressor; and 
 a first expansion device in fluid communication with the first fluid circuit; 
 
 a second refrigeration stage defining a second fluid circuit that is fluidically isolated from the first fluid circuit for circulating a second refrigerant, the second refrigeration stage having:
 a second condenser; 
 a second compressor; and 
 a second expansion device in fluid communication with the second fluid circuit, the second expansion device comprising:
 a first capillary tube and a second capillary tube in parallel flow arrangement; and 
 a second stage valve in fluid communication with the second capillary tube for selectively controlling flow of the second refrigerant through the second capillary tube in response to at least one operating condition of the refrigeration system without interrupting flow of the second refrigerant through the first capillary tube; and 
 
 
   at least one interstage heat exchanger in heat transferring communication with the first and second fluid circuits to exchange heat between the first and second refrigerants,   wherein the first and second refrigeration stages are configured in a cascade cooling arrangement.   
     
     
         17 . The freezer of  claim 16 , wherein the first fluid circuit further comprises:
 a first fluid line in fluid communication with an outlet of the first condenser and a first inlet of the at least one interstage heat exchanger, the first fluid line including the first expansion device;   a first suction line in fluid communication with a first outlet of the at least one interstage heat exchanger and an inlet of the first compressor; and   a first heat exchanger defined by a portion of the first fluid line being in heat transferring communication with a portion of the first suction line or a portion of the first expansion device to thereby exchange heat between the first refrigerant flowing through the first fluid line and the first refrigerant flowing through the first suction line.   
     
     
         18 . The freezer of  claim 16 , wherein the second fluid circuit further comprises:
 a second fluid line in fluid communication with a second outlet of the at least one interstage heat exchanger and an inlet of the evaporator, the second fluid line including the second expansion device;   a second suction line in fluid communication with an outlet of the evaporator and an inlet of the second compressor; and   a second heat exchanger defined by a portion of the second fluid line or a portion of the second expansion device being in heat transferring communication with a portion of second suction line to thereby exchange heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.   
     
     
         19 . The freezer of  claim 17 , wherein the second fluid circuit further comprises:
 a second fluid line in fluid communication with a second outlet of the at least one interstage heat exchanger and an inlet of the evaporator, the second fluid line including the second expansion device;   a second suction line in fluid communication with an outlet of the evaporator and an inlet of the second compressor; and   a second heat exchanger defined by a portion of the second fluid line or the second expansion device being in heat transferring communication with a portion of second suction line to thereby exchange heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.   
     
     
         20 . The freezer of  claim 16 , wherein the first expansion device further comprises:
 a third capillary tube and a fourth capillary tube in parallel flow arrangement; and   a first stage valve for selectively controlling flow of the first refrigerant through the fourth capillary tube in response to at least one operating condition of the refrigeration system without interrupting flow of the first refrigerant through the third capillary tube.   
     
     
         21 . The freezer of  claim 20 , wherein the first fluid circuit further comprises:
 a first fluid line in fluid communication with an outlet of the first condenser and a first inlet of the at least one interstage heat exchanger, the first fluid line including the first expansion device;   a first suction line in fluid communication with a first outlet of the at least one interstage heat exchanger and an inlet of the first compressor; and   a first heat exchanger defined by a portion of the first suction line being in heat transferring communication with a portion of the first fluid line or a portion of the first expansion device to thereby exchange heat between the first refrigerant flowing through the first fluid line and the first refrigerant flowing through the first suction line.   
     
     
         22 . The freezer of  claim 21 , wherein the second fluid circuit further comprises:
 a second fluid line in fluid communication with a second outlet of the at least one interstage heat exchanger and an inlet of the evaporator, the second fluid line including the second expansion device;   a second suction line in fluid communication with an outlet of the evaporator and an inlet of the second compressor; and   a second heat exchanger defined by a portion of the second fluid line or a portion of the second expansion device being in heat transferring communication with a portion of second suction line to thereby exchange heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.