Mirror image technique for the thermal analysis in cryoablation: Experimental setup and validation

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The paper presents a set of experiments that were performed to characterize the freezing front propagation in water first, and in an agar-gel solution afterwards. The experimental setup made of Peltier devices, to emulate the cryogenic effect, and a copper cold finger, to mimic the cold probe interface, are described. We claim that by monitoring some temperatures at the generating cryodevice, several pieces of information can be derived through the cold interface to assess the outside thermodynamic changes. The employed technique, known as mirror image, allows determining the occurrence of the initial ice formation outside the cryo-probe and in the surrounding material, also with different magnitudes of the thermal contact resistance at the cold interface. For both water and agar the ice penetration was found to be non linear versus time, and proportional to the square root of time in the performed experiments. The ice drift velocity decreases according to its penetration inside the tested materials. At the beginning of ice formation, the measured drift velocities are approximately 0.11 mm/s and 0.06 mm/s for water and agar, respectively, and after the ice penetrates 2 mm, they become approximately 0.03 mm/s for both materials.