Experimental Apparatus for Measuring the Performance of a Precooled Mixed Gas Joule Thomson Cryosurgical Probe

Cryosurgery is a technique for destroying undesirable tissue such as cancers using a freezing process. A previous paper referenced here describes the development of a thermodynamic modeling tool for a precooled Mixed Gas Joule-Thomson (MGJT) cryoprobe used for cryosurgery. An experimental test facility has been constructed to capture the performance of a precooled MGJT cryoprobe; the experimental data will be used to tune and verify the model. The test facility is flexible relative to working fluid, charge pressure, pressure ratio, and flow rate. Therefore, the facility can also be used to demonstrate additional cooling capacity available with the optimal mixture compositions and operating parameters selected by the model. A commercially available cryoprobe system has been disassembled and installed in a vacuum insulated dewar. The system has been modified in order to integrate a suite of measurement instrumentation that can completely characterize the performance of individual components as well as the overall system. Measurements include sufficient temperature and pressure sensors to resolve thermodynamic states and flow meters to calculate heat and work transfer rates. A thermal load is applied to the cycle using an electric heater to characterize the refrigeration performance. Temperature sensors are also integrated within the recuperator in order to capture the heat transfer performance of the two-phase, multi-component mixture as it flows through the recuperator. An uncertainty analysis for the experiment is presented in this paper and shows that the performance metrics can be computed from the experimental data to within 10% uncertainty under the nominal anticipated operating conditions using both a synthetic refrigerant and hydrocarbon based gas mixture. Preliminary data are reduced to demonstrate the capability of the test facility.