A cooling system for cooling a hot material comprising a cooling chamber, a heat exchanger in the chamber, gas circulating means for forcing a cooling gas within the chamber in a closed circuit that includes cooling contact with the heat exchanger, means for passing the hot material from a source thereof through the heat exchanger and back to the source and means for selectively providing an additional cooling medium to the cooling system such as a flowable cryogen and particularly a cryogen gas.
The refrigeration available in a liquefied gas is utilized to refrigerate a fluid having a boiling point above the boiling point of the liquefied gas which is sprayed into an endless conduit such that the liquefied gas is vaporized. The resulting thermal currents and momentum of the spray are effective to provide the motive power for circulating the gas throughout the conduit and into indirect heat exchange with the fluid to be refrigerated. The temperature of heat exchange means in the vicinity of the location at which the fluid is introduced into such indirect heat exchange may be regulated by controlling the magnitude of the gas flow throughout the conduit to thereby avoid freezing of components of such fluid. The use of shaft power (such as a fan or blower) for circulating the gas flow throughout the conduit is avoided and the utilization of refrigeration available in the liquefied gas is improved accordingly.
The invention is a technique for dynamic measurements of the heat transfer coefficient to the outer layer of the skin surface using a high thermal conductivity metal in an insulating block as the standardized target. The coefficient is dependent on the specific design of the cryogen valve and nozzle, and values up to 11 500 W/m.sup.2 K values were measured for a 100 ms long spurts. The values for longer spurts are dependent on air humidity, as ice/snow formation then tends to form a thermally insulating layer. The average value of the heat transfer coefficient for a 200 ms long spurt was determined to 8000 W/m.sup.2 K for conditions of normal room humidity and temperature. The technique enables an improved prediction of the temperature profile and cooling efficiency during therapy, and may thereby contribute to an improved therapeutic outcome.
This invention is directed to an external loop nonfreezing heat exchanger for cooling a heat transfer fluid with cryogenic fluid. The cryogenic fluid is first pre-vaporized with the spent cryogenic fluid. The heat transfer fluid is then cooled by the vaporized cryogenic fluid instead of the cryogenic fluid feed directly.
