Cryogenic Heat Transfer Optimization of the Freezing Front Generated by a Cryoprobe
This paper is concerned with the analysis and optimization technique of the freezing front generated by a cryoprobe. The method, which is based on the placing of a flat cryoprobe against a body of tissue studies the resulting freezing front and optimizes the heat transfer, minimizing also the unnecessary freezing of the tissue. The optimization procedure is illustrated using a flexible model that starts from a one dimensional simplified situation and then is extended to a three-dimensional model that accounts for the density change of the tissue and the movement upon the readings of thermocouples placed at various depths in the tissue. The model uses an iterative procedure that continues until the optimal value is reached and the unnecessary freezing is minimized. The model can be used in a number of different ways, for example to study the behaviour over the entire range of acceptable parameters, to test the possible effects of density change or to obtain simple estimates of the system behaviour in specific conditions. Using data fitting techniques, optimized values were obtained over the range from body temperature (310 K) to that of liquid nitrogen probe (73 K). For the model considered here, the optimization technique shows that the optimal value for density ration was found to be 1.085 and the minimization of the unnecessary freezing is reachable using an extensive approach that covers the entire range of parameters.
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