Temperature control system for liquid nitrogen refrigerator

A liquid nitrogen refrigerator in which materials may be stored in a nitrogen gas atmosphere in a vapor-stage storage area above a body of liquid nitrogen having a top free surface, including a refrigeration chamber having a closed bottom and an open top normally closed by a door, a fill tube having an outlet adjacent the bottom of the refrigeration chamber for admitting liquid nitrogen into the chamber below the level of the top free surface of the body of liquid nitrogen, high and low level sensors in the chamber to sense the level of liquid nitrogen and produce a signal in response to the liquid nitrogen reaching predetermined high and low levels, conduit means connecting a supply of liquid nitrogen to the fill tube through a power operated valve, and a controller responsive to signals from the high and low level sensors for actuating the power operated valve to maintain the liquid nitrogen in the chamber between an upper and a lower level determined by the high and low level sensors, the improvement comprising,

• temperature sensing means in the refrigeration chamber for sensing the temperature at a predetermined location above the top free surface of the body of liquid nitrogen and producing a signal representative of the temperature sensed,
• second conduit means connected to the supply of liquid nitrogen and extending into said chamber,
• a second power operated valve connected to said second conduit means,
• a spray nozzle connected to said second conduit within said chamber at a location adjacent said door, and
• gas temperature control means responsive to said temperature sensing means for producing turbulence in the nitrogen gas atmosphere in the chamber when the sensed temperature exceeds a predetermined level to thereby reduce the temperature of the gaseous nitrogen atmosphere at said predetermined level, said temperature control means being operable in response to a signal from said temperature sensing means to open and close said second power operated valve to admit a pulse of liquid nitrogen to flow through said second conduit means and discharged as an atomized spray in the nitrogen gas atmosphere adjacent the top of the chamber whereby the atomized spray of liquid nitrogen absorbs heat of vaporization from the warmer nitrogen gas atmosphere adjacent the top of said chamber to produce turbulence and reduce the temperature differential in the nitrogen gas in the atmosphere throughout the chamber, said pulse of liquid nitrogen being of sufficiently short duration as to be substantially completely vaporized in the gaseous nitrogen atmosphere whereby the level of liquid nitrogen in the chamber is not effected by said atomized spray.

A method of controlling the temperature in the storage area of a liquid nitrogen refrigerator in which materials may be stored in a nitrogen gas atmosphere in a vapor-stage storage area above a body of liquid nitrogen having a top free surface, the refrigerator including a refrigeration chamber having a closed bottom and an open top normally closed by a door, a fill tube having an outlet adjacent the bottom of the refrigeration chamber for admitting liquid nitrogen into the chamber below the level of the top free surface of the body of liquid nitrogen, a liquid nitrogen conduit connecting a supply of liquid nitrogen to the fill tube through a power operated valve, and a liquid nitrogen controller responsive to signals from a high level and a low level liquid nitrogen sensor in the chamber for actuating the power operated valve to maintain the liquid nitrogen level in the chamber within a range determined by the high and low level sensors, the improvement wherein said method comprises

• sensing the temperature in the refrigerator at a predetermined level above the top free surface of the liquid nitrogen and producing a signal representative of the temperature sensed, and
• inducing turbulence in the nitrogen gas atmosphere in the chamber in response to a sensed temperature exceeding a predetermined level by gasifying liquid nitrogen from the liquid nitrogen supply, admitting the gasified nitrogen into the fill tube, and discharging the gaseous nitrogen below the free surface of the liquid nitrogen in the chamber to thereby produce turbulence in the liquid nitrogen and in the nitrogen gas atmosphere thereabove to thereby produce a more uniform temperature throughout the storage area.

A method of controlling the temperature in the storage area of a liquid nitrogen refrigerator in which materials may be stored in a nitrogen gas atmosphere in a vapor-stage storage area above a body of liquid nitrogen having a top free surface, the refrigerator including a refrigeration chamber having a closed bottom and an open top normally closed by a door, a fill tube having an outlet adjacent the bottom of the refrigeration chamber for admitting liquid nitrogen into the chamber below the level of the top free surface of the body of liquid nitrogen, a liquid nitrogen conduit connecting a supply of liquid nitrogen to the fill tube through a power operated valve, and a liquid nitrogen controller responsive to signals from a high level and a low level liquid nitrogen sensor in the chamber for actuating the power operated valve to maintain the liquid nitrogen level in the chamber within a range determined by the high and low level sensors, the improvement wherein said method comprises

• sensing the temperature in the refrigeration chamber at a predetermined level above the top free surface of the liquid nitrogen and producing a signal representative of the temperature sensed,
• providing a second conduit connected to the supply of liquid nitrogen and extending into said chamber,
• providing a second power operated valve connected in the second conduit,
• providing a spray nozzle on the end of the second conduit within said chamber at a location adjacent the door, and
• opening and closing the second power operated valve in response to signals from the sensed temperature to admit pulses of liquid nitrogen to flow through the second conduit and nozzle and be discharged as an atomized spray into the nitrogen gas atmosphere adjacent the top of the chamber whereby the atomized spray of liquid nitrogen absorbs heat of vaporization from the warmer nitrogen gas atmosphere adjacent the top of the chamber to produce turbulence in the nitrogen gas atmosphere in the vapor-stage storage area of the chamber and reduce the temperature differential in the nitrogen gas in the atmosphere throughout the chamber, said pulse of liquid nitrogen being of sufficiently short duration as to be substantially completely vaporized in the gaseous nitrogen atmosphere whereby the level of liquid nitrogen in the chamber is not effected by said atomized spray.