High efficiency very-low temperature mixed refrigerant system with rapid cool down

Abstract

The present invention is a refrigeration system that uses a nonflammable, nonchlorinated refrigerant mixture to achieve very-low temperatures using a single compressor. The system is characterized by both high efficiency and rapid cool down time.

What is claimed is:  
     
         1 . A low temperature closed cycle refrigeration system comprising: 
 a single compressor with an outlet delivering a refrigerant flow at high pressure and an inlet receiving said refrigerant flow at low pressure;    a condenser unit receiving said high-pressure refrigerant flow from said compressor and removing heat therefrom;    an evaporator receiving said refrigerant flow from said condenser unit at low pressure and low temperature and returning said refrigerant flow to said compressor inlet;    a flow metering device between said condenser unit and said evaporator to reduce said high pressure from said compressor to said low pressure in said evaporator and to lower the temperature of said refrigerant flow; and    a refrigerant circulating in said closed cycle without refrigerant freeze-out at said low pressure, said refrigerant being a mixed refrigerant, the components of said mixed refrigerant having a range of respective normal boiling temperatures of at least 50° C.    
     
     
         2 . A refrigeration system as in  claim 1 , wherein said mixed refrigerant is composed in mole percentage of the following: 
 at least one of Argon and nitrogen in a range of 0 to 20%    R-14 in a range of 20-60%;    R-23 in a range of 10-40%;    R-125 in a range of 4-30%;    R-134a in a range of 0-30%;    at least one of the following high boiling components: 
 R-236fa, R-245fa, and E-137.  
   
     
     
         3 . A refrigeration system as in  claim 1 , wherein said mixed refrigerant is 53 mole percent of R-14; 19 mole percent of R-23; 7 mole percent of R-125, and 21 percent of R-236fa.  
     
     
         4 . The refrigeration system of  claim 2 , and further comprising a control valve receiving said low pressure refrigerant flow from said evaporator and outputting said refrigerant flow to said compressor inlet, said control valve maintaining a selected level of said low pressure at an inlet of said control valve and controlling said evaporator pressure.  
     
     
         5 . A refrigeration system as in  claim 2 , wherein said evaporator includes a helical coil of finned tubing located in a first cylinder, said finned tubing being wrapped around a second cylinder within said first cylinder, said evaporator cooling a coolant that flows within said first cylinder and over said finned tubing in a cross-flow/counter flow arrangement, said refrigerant flow through said finned tubing exchanges heat and cools said coolant.  
     
     
         6 . The refrigeration system as in  claim 5 , further comprising: 
 a heat exchanger receiving refrigerant flow at high pressure from said condenser and delivering said high pressure refrigerant to said flow metering device, said flow refrigerant flow from said evaporator being in heat exchange relationship with said high pressure refrigerant flow in said heat exchanger.    
     
     
         7 . Refrigeration system as in  claim 6 , wherein said control valve is between said heat exchanger and said compressor inlet.