Kendra Passow M.S. Graduate Student Mechanical Engineering Room: 1327 ERB Email: passow@wisc.edu Home Town: Maple Plain, Minnesota Thesis: Experimental modeling of a surgical cryoprobe

Cryosurgery A technique for destroying undesirable tissue such as cancers using a freezing process Used to ablate prostate and liver cancer tumors Also used in a variety of procedures in dermatology, gynecology, and cardiology Relies on cryosurgical probe that is inserted into the body in order to create the necessary cryogenic temperatures (~150-180 K) The cryolesion that is formed is typically on the order of tens of millimeters in diameter and the lethal zone extends outward into the tissue from the cryoprobe tip approximately to the location where the tissue is about 240 K

Project Goals Develop a modeling tool for optimizing gas mixtures and operating conditions for a precooled mixed gas JT cycle used for cryosurgery. 1. Improvement of model used to optimize performance and design of a cryosurgical probe Verify accuracy of mixture property data used in the model at cryogenic temperatures Develop empirically tuned heat exchanger models for the multi-phase, multi-component mixtures Improve system level refrigeration performance predictive capability 2. Experimental data Measure relevant system thermodynamic states Quantify performance over a range of mixtures and operating conditions Compute component- and system-level performance and compare with modeled predictions Schematic of 2-stage mixed gas Joule-Thompson cryosurgical probe system recuperator

Experimental Setup The test facility was built to simulate cryoprobe performance during surgery Pressure, temperature, and mass flow measurements quantify thermodynamic states and heat transfers Thermal load of warm tissue simulated using a heater Interchangeable jewel orifice used to modify the pressure and mass flow applied to the cycle Jewel orifice piece for Joule-Thompson expansion Cold components of experimental test facility enclosed in vacuum chamber