Method and apparatus for measuring the heat transfer coefficient during cryogen spray cooling of tissue

摘要

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/m²K 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/m²K 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.