WORKING SUBSTANCES WITH THE ?LIQUID-SOLID BODY-LIQUID? PHASE TRANSITION FOR CRYOSURGICAL APPARATUSES

An autonomous cryosurgical apparatus that uses latent heat of melting of a prefrozen working substance as a source of cold is considered in the present article. The process of the substance freezing is taking place in a cold accumulator that represents a hermetically sealed container. In the course of the phase transitions “liquid - solid body ? liquid” amount of the working substance is unchangeable and therefore the cold accumulator can be used repeatedly. A separate refrigerating machine could be used to freeze the working substance in the accumulator and this makes the peculiarity of the apparatus. A Joule-Thomson refrigerating machine of a simple design with a phase separator and operating by use of a zeotropic mixture of refrigerants can advisably be used for this purpose. Thermophysical properties of more than 20 substances candidates with melting temperatures within the range of (-100…-150)°С that is acceptable to the apparatus operating conditions are presented in the article. Ethanol seems to be the most appropriate agent which is in a liquid state under the normal conditions; has the melting/freezing temperature of -114°С and the latent heat of phase transition “solid body ? liquid” of 104.4 kJ/kg.