Hydrofluoroethers as low temperature refrigerants

Abstract

A method and apparatus are provided for using certain hydrofluoroethers (HFEs) as low temperature heat transfer media in secondary loop refrigeration systems. These materials exhibit a low, somewhat linear Temperature Difference Factor over the temperature range of −15° C. to −65° C., making them ideal for use as low temperature heat transfer media. The HFEs of the present invention are nonflammable, nontoxic, environmentally benign, and have a high heat transfer capacity and low viscosity over the required operating temperatures. Furthermore, since these materials have high boiling points and low freezing points, they are not prone to phase changes over the required operating temperatures, and do not require pressurized systems.

What is claimed is:  
     
       1. A method for transferring heat, comprising the steps of: 
       providing a heat source;  
       providing a heat sink; and  
       transferring heat between the heat source and the heat sink through the use of a heat transfer medium comprising a fluorinated other;  
       wherein the heat sink is cooled to a temperature of less than about −15° C. 
     
     
       2. The method of claim  1 , wherein the fluorinated ether is a compound of the formula 
       
         
           R 1 —O—R 2    
         
       
       wherein R 1  and R 2  are the same or different and together contain at least three carbon atoms, wherein at least one of R 1  and R 2  contains at least one fluorine atom, and wherein the total number of hydrogen atoms in the compound is at most equal to the number of fluorine atoms. 
     
     
       3. The method of claim  2 , wherein R 1  and R 2  are the same or different and are selected from the group consisting of alkyl, aryl, or alkylaryl moieties. 
     
     
       4. The method of claim  1 , wherein the fluorinated ether is a compound of the formula 
       
         
           R 1 —O—R 2    
         
       
       wherein R 1  is a moiety containing at least one partially fluorinated alkyl, aryl, or alkylaryl group, and wherein R 2  is a moiety containing at least one non-fluorinated alkyl, aryl, or alkyl aryl group. 
     
     
       5. The method of claim  4 , wherein is R 1  is a partially fluorinated alkyl group, and wherein R 2  is a non-fluorinated alkyl group. 
     
     
       6. The method of claim  1 , wherein the fluorinated ether contains only carbon, hydrogen, oxygen, and fluorine. 
     
     
       7. The method of claim  1 , wherein the fluorinated ether is a compound of the formula 
       
         
           R f —O—R  
         
       
       wherein R f  is a perfluorinated alkyl, aryl, or alkylaryl group, and wherein R is a nonfluorinated alkyl, aryl, or alkylaryl group. 
     
     
       8. The method of claim  7 , wherein R f  is a perfluorinated alkyl group and R areis a non- fluorinated  alkyl groups . 
     
     
       9. The method of claim  1 , wherein the fluorinated ether is selected from the group consisting of C 3 F 7 OCH 3 , C 4 F 9 OCH 3 , and C 4 F 9 OC 2 H 5 . 
     
     
       10. The method of claim  1 , wherein the heat transfer medium is cooled to less than about −15° C. 
     
     
       11. The method of claim  1 , wherein the heat transfer medium is cooled to less than about −25° C. 
     
     
       12. The method of claim  1 , wherein the heat transfer medium has a temperature difference factor of less than about 0.00375 Kg 2/7 m 2 s 1/3  at −25° C. 
     
     
       13. The method of claim  1 , wherein the temperature difference factor of the heat transfer medium shows a substantially linear dependence on temperature over the temperature range of −15° C. to −45° C. 
     
     
       14. The method of claim  1 , wherein the temperature difference factor of the heat transfer medium shows an substantially linear dependence on temperature over the temperature range of 30° C. to −60° C. 
     
     
       15. The method of claim  13 , wherein the first derivative of the temperature difference factor with respect to temperature over the temperature range of −15° C. to −45° C. is within the range of about 0 to about −1.6×10 −4 Kg 2/7 m 2 s 1/3 /J+C. 
     
     
       16. The method of claim  12 , wherein the second derivative of the temperature difference factor with respect to temperature over the temperature range of −15° C. to −45° C. is about 0. 
     
     
       17. The method of claim  1 , wherein the fluorinated ether has no flash point. 
     
     
       18. The method of claim  1 , wherein the heat transfer factor of the fluorinated ether is less than about 650 J/(s 1/3 m 8/3 °C.) at −35° C. 
     
     
       19. The method of claim  1 , wherein the pressure drop factor of the fluorinated ether is less than about 9.75 kg/(m 1.3/5 s 1/5 ) at temperatures greater than about −40° C. 
     
     
       20. The method of claim  1 , wherein the ratio of the pump power of the fluorinated ether to the pump power of C 4 F 9 OCH 3  is less than about 1 at −25° C. 
     
     
       21. The method of claim  1 , wherein the ratio of the pump power of the fluorinated ether to the pump power of C 4 F 9 OCH 3  is less than about 3 at temperatures between −25° C. and −45° C. 
     
     
       22. The method of claim  1 , wherein the heat sink is a primary refrigeration system. 
     
     
       23. A method for transferring heat between a heat source and a heat sink, comprising the steps of: 
       transferring heat from the heat source to a fluorinated ether; and  
       transferring heat from the fluorinated ether to the heat sink;  
       wherein the heat sink is cooled to less than about −15° C., and wherein the fluorinated ether is a compound selected from the group consisting of C 3 F 7 OCH 3 , C 4 F 9 OCH 3 , and C 4 F 9 OC 2 H 5 . 
     
     
       24. A method for transferring heat, comprising the steps of: 
       providing a heat source;  
       providing a heat sink; and  
       transferring heat between the heat source and the heat sink through the use of a heat transfer medium comprising a material having a Temperature Difference Factor of less than about 0.00375 (Kg 2/7 m 2 s 1/3 )/J at −25° C;  
       wherein the heat sink is cooled to a temperature of less than about −15° C. 
     
     
       25. A heat transfer system, comprising: 
       a heat source;  
       a heat sink; and  
       heat transfer means for transferring heat between said heat source and said heat sink;  
       wherein said heat transfer means comprises a fluorinated ether, and wherein said heat sink is cooled to less than about −15° C. 
     
     
       26. The system of claim  25 , wherein said heat transfer means is a secondary loop refrigeration system. 
     
     
       27. A refrigeration system, comprising: 
       a first  second refrigeration loop for transferring heat from a heat source to a first  second heat transfer medium; and  
       a second  first refrigeration loop for transferring heat from said first  second heat transfer medium to a second  first heat transfer medium;  
       wherein said first  second heat transfer medium comprises a fluorinated ether and is cooled to less than about −15° C. by said second  first refrigeration loop. 
     
     
       28. The refrigeration system of claim  27 , further comprising: accelerating means for accelerating the rate at which heat is transferred from said heat source to said second heat transfer medium. 
     
     
       29. The refrigeration system of claim  28 , wherein said accelerating means induces a turbulent flow in the atmosphere between said heat source and said first  second refrigeration loop. 
     
     
       30. The refrigeration system of claim  28 , wherein said accelerating means is a high velocity fan. 
     
     
       31. A method for transferring heat from a heat source to a heat sink, comprising the steps of: 
       providing a heat source, a first heat transfer medium, and a second heat transfer medium comprising a fluorinated ether which is cooled to less than about −15° C.;  
       transferring heat from the heat source to the first  second heat transfer medium; and  
       transferring heat from the first  second heat transfer medium to the second  first heat transfer medium.  
     
     
       32. The method of claim  31 , wherein the first and second heat transfer media are disposed in separate refrigeration coils. 
     
     
       33. The method of claim  31 , wherein the transfer of heat from the first heat transfer medium to the second heat transfer medium heats the second heat transfer medium to above −15° C. 
     
     
       34. The method of claim  33 , further comprising the step of: 
       cooling the second heat transfer medium down to less than about −15° C.