Modeling and Optimization of a Two-Stage Mixed-Gas Joule-Thomson Cryoprobe System

Cryosurgery is a technique for destroying undesirable tissue, such as cancers, by exposing it to a very low temperature. This paper presents a thermodynamic modeling tool that has been developed for a two stage, mixed gas Joule-Thomson (MGJT) cryoprobe used for cryosurgery. A conventional vapor compression (VC) cycle using a pure refrigerant precools the MGJT cycle providing refrigeration at the cryoprobe tip. The model is integrated with an optimization routine, in order to investigate the optimal mixture composition for different cryoprobe tip temperatures and identify the optimal precooling temperature. The cryoprobe system performance is reported in terms of cryoprobe conductance (related to size) and compressor displacement. The results for the two stage system are compared to the performance of a single stage MGJT cycle in order to demonstrate the benefits and limitations associated with the addition of the precooling cycle.