Supplemental refrigeration using nitrogen

Abstract

Disclosed are methodology and apparatus useful to employ liquid nitrogen cryogen to boost on demand the refrigeration capacity of a freezer or similar device in which refrigeration is provided by a mechanical refrigeration circuit.

What is claimed is: 
     
         1 - 63  (canceled) 
     
     
         64 . A method of modifying a refrigeration apparatus,
 wherein said refrigeration apparatus comprises an enclosure comprising air cooled by a mechanical refrigeration circuit, said method comprising:   adding a supplemental refrigeration system comprising one or more supplemental heat exchangers each having an inlet coupled to a source of liquid nitrogen and an outlet coupled to a vent that is open to an external atmosphere, further comprising a means of moving air cooled by the mechanical refrigeration circuit from said enclosure to contact the exterior surfaces of said one or more supplemental heat exchangers and to establish fluid communication with the enclosure,   wherein the supplemental refrigeration system is either physically attached to the outside of the enclosure and/or uses associated ducts to route air cooled by the mechanical refrigeration circuit from the enclosure over to the said one or more supplemental heat exchangers,   wherein the added supplemental refrigeration system further comprises a control mechanism that controls the flow of liquid nitrogen from said nitrogen source into one or more of the supplemental heat exchangers to cool air in contact with the exterior surfaces of said one or more of the supplemental heat exchangers;   wherein the control mechanism:
 i. enables and controls the flow of liquid nitrogen into one or more of the supplemental heat exchangers when the temperature of the air in the enclosure that is being cooled by the mechanical refrigeration circuit is warmer than a set point temperature set by the operator, or 
 ii. enables and controls the flow of liquid nitrogen into one or more of the supplemental heat exchangers by monitoring the pressure of liquid nitrogen flowing from said nitrogen source, or 
 iii. enables and controls the flow of liquid nitrogen into one or more of the supplemental heat exchangers by monitoring the pressure of gaseous nitrogen leaving one or more of the supplemental heat exchangers, or 
 iv. enables and controls the flow of liquid nitrogen into one or more of the supplemental heat exchangers by monitoring the pressure of liquid nitrogen flowing from said nitrogen source and monitoring the pressure of gaseous nitrogen leaving one or more of the supplemental heat exchangers, or 
 v. when the cooling of the air in the mechanically cooled space by mechanical refrigeration is at the maximum that can be provided by said mechanical refrigeration circuit or is within a preset 90% of that maximum. 
   
     
     
         65 . The method according to  claim 64  wherein the added supplemental refrigeration system further comprises a mechanism configured to melt ice that has formed on the surface of one or more of the supplemental heat exchangers. 
     
     
         66 . The method according to  claim 64  wherein said modifying the refrigeration apparatus comprises adding means for isolating one or more of the supplemental heat exchangers from said refrigeration apparatus. 
     
     
         67 . The method according to  claim 64  which comprises modifying the refrigeration apparatus by adding a recycle line in fluid communication with said supplemental heat exchanger and having an inlet between the outlet of the supplemental heat exchanger and said vent and having an outlet between the inlet of the supplemental heat exchanger and said source of liquid nitrogen, and wherein said recycle line comprises an impeller that can impel flow of nitrogen in said recycle line and a heater that can heat nitrogen that is in said recycle line, wherein said modification comprises adding a control mechanism that enables the flow of nitrogen to be alternated between a first mode in which nitrogen can flow from the outlet of the supplemental heat exchanger into said recycle line and not to said vent and nitrogen from said recycle line that has been heated by said heater and not liquid nitrogen from said source thereof can flow into the inlet of said supplemental heat exchanger and the nitrogen from said recycle line can be recycled into said supplemental heat exchanger repeatedly, and a second mode in which nitrogen can flow from the outlet of said supplemental heat exchanger to said vent and not into said recycle line, and liquid nitrogen from said source and not nitrogen from said recycle line can flow into the inlet of said supplemental heat exchanger. 
     
     
         68 . An apparatus for refrigerating a product, said apparatus comprising:
 a mechanical refrigeration circuit that cools air in an enclosure comprising air,   one or more supplemental heat exchangers which have an inlet coupled to a source of liquid nitrogen and an outlet coupled to a vent that is open to an external atmosphere outside the apparatus, wherein the air cooled by the mechanical refrigeration circuit and flowing from the enclosure is further cooled by heat exchange contact with the one or more supplemental heat exchangers, and   a control mechanism for controlling the flow of liquid nitrogen into said one or more supplemental heat exchangers to cool said air, wherein said control mechanism:
 i. enables and controls the flow of liquid nitrogen into one or more of the supplemental heat exchangers when the temperature of the atmosphere in the mechanically cooled space that is being cooled by the mechanical refrigeration circuit is warmer than a set point temperature set by the operator, or 
 ii. enables and controls the flow of liquid nitrogen into one or more of the supplemental heat exchangers by monitoring the pressure of liquid nitrogen flowing from said nitrogen source, or 
 iii. enables and controls the flow of liquid nitrogen into one or more of the supplemental heat exchangers by monitoring the pressure of gaseous nitrogen leaving one or more of the supplemental heat exchangers, or 
 iv. enables and controls the flow of liquid nitrogen into one or more of the supplemental heat exchangers by monitoring the pressure of liquid nitrogen flowing from said nitrogen source and monitoring the pressure of gaseous nitrogen leaving one or more of the supplemental heat exchangers, or 
 v. enables said flow when it senses that the temperature of the atmosphere in the enclosure is higher than a temperature that corresponds to the cooling provided by said mechanical refrigeration circuit being within 90% of said maximum. 
   
     
     
         69 . The apparatus of  claim 68  which further comprises a recycle line for heated nitrogen in fluid communication with said supplemental heat exchanger and having an inlet between the outlet of the supplemental heat exchanger and said vent and having an outlet between the inlet of the supplemental heat exchanger and said source of liquid nitrogen, and wherein said recycle line comprises an impeller that can impel flow of nitrogen in said recycle line and a heater that can heat nitrogen that is in said recycle line, wherein said heated nitrogen flows repeatedly through said recycle line into said supplemental heat exchanger and melts ice formed on a surface of said supplemental heat exchanger. 
     
     
         70 . The apparatus according to  claim 68  that further comprises a supplemental impeller for said one or more of the supplemental heat exchangers for circulating air from and to the enclosure. 
     
     
         71 . The apparatus according to  claim 68  containing at least one modular cooling unit containing one or more of the supplemental heat exchangers, an air-supply subunit having one or more supplemental impellers, an air return subunit, and a control subunit. 
     
     
         72 . A method of refrigerating a product, the method comprises:
 providing the product in an enclosure that contains air,   operating a mechanical refrigeration unit up to a maximum refrigeration capacity that can be provided by said mechanical refrigeration unit or is within a preset percentage below said maximum refrigeration capacity to cool said air, and   operating a supplemental refrigeration system comprising one or more supplemental heat exchangers, in concert with, but separately from, said mechanical refrigeration unit to provide additional refrigeration capacity to further cool said air,   wherein said additional refrigeration capacity is provided by controllably flowing liquid nitrogen from a source of liquid nitrogen into one or more of the supplemental heat exchangers:
 i. when the temperature of the air cooled by the mechanical refrigeration unit is warmer than a set point temperature set by the operator, or 
 ii. when the cooling of the air by the mechanical refrigeration unit is at the maximum refrigeration capacity that can be provided by said mechanical refrigeration unit or is within a preset 90% of that maximum refrigeration capacity, and 
 adjusting the additional refrigeration capacity by: 
 i. controlling the flow of liquid nitrogen into one or more of the supplemental heat exchangers by monitoring the pressure of liquid nitrogen flowing from said nitrogen source, or 
 ii. controlling the flow of liquid nitrogen into one or more of the supplemental heat exchangers by monitoring the pressure of gaseous nitrogen leaving one or more of the supplemental heat exchangers, or 
 iii. controlling the flow of liquid nitrogen into one or more of the supplemental heat exchangers by monitoring the pressure of liquid nitrogen flowing from said nitrogen source and monitoring the pressure of gaseous nitrogen leaving one or more of the supplemental heat exchangers. 
   
     
     
         73 . The method according to  claim 72  which further comprises:
 routing the nitrogen leaving said supplemental heat exchanger to a vent that is open to an external atmosphere, and not to a recycle line, and flowing the liquid nitrogen from said source of liquid nitrogen and not the nitrogen from said recycle line into the inlet of said supplemental heat exchanger, or 
 routing the nitrogen leaving said supplemental heat exchanger to a recycle line which is in fluid communication with the inlet of said supplemental heat exchanger, and not to the vent, and flowing said nitrogen in the recycle line after heating and not the liquid nitrogen from said source thereof into the inlet of said supplemental heat exchanger, wherein said heated nitrogen flows repeatedly through said recycle line into said supplemental heat exchanger and melts ice formed on a surface of said supplemental heat exchanger. 
 
     
     
         74 . The method according to  claim 72  wherein the supplemental refrigeration system or one or more of the supplemental heat exchangers is either physically attached to the outside of the enclosure and/or uses associated ducts to establish fluid communication with the enclosure.