Experimental and Numerical Study of One, Two, and Three Embedded Needle Cryoprobes Simultaneously Operated by High Pressure Argon Gas

One, two, and three needle cryoprobes, $1.47mm$ outside diameter, simultaneously and uniformly operated by high pressure argon gas, were tested in a gel simulating the thermal properties of biological tissues. The probes were inserted into the same depth in the gel through two parallel templates with holes drilled on a $5×5mm2$ mesh. The temperature of the active segment of the probe was monitored by a single soldered thermocouple (TC). Temperatures in the gel were monitored by K-type TC strings in the radial, and in the downward and upward axial directions. The phase-change problem in the gel was solved by ANSYS7.0, based on the enthalpy method. Calculated and measured results compared reasonably well with the most deviations observed in the upward axial direction. Results of this study may be summarized as follows: (a) Due to the cylindrical structure of the probe, the advancement of the frozen fronts was more pronounced in the upward axial and the radial directions than in the downward direction. (b) The farthest placement of the two probes $(10mm)$ yielded the largest volumes enclosed by the isothermal contours. (c) In the tightest two placement configurations of the three probes, the $−40°C$ fronts of all frozen lumps have joined together even after $1min$ of operation, while in the less tight configurations, joining occurred later. (d) In multiprobe applications and for a given duration of application, there exists a certain placement configuration that will produce the maximal volume of any temperature-specific frozen lump. The computational tool presented in this study could assist the surgeon in the preplanning of cryosurgical procedures and thus reduce uncertainties and enhance its success rate.