Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.
The first step of organ cryopreservation is a cryoprotectant perfusion, which can speed cooling. The temperature of the kidney decreased from 37℃ to about 0℃ by perfusion. During the kidney perfusion process, the cryoprotectant enters the kidneys through the renal artery and leaves the kidneys through the renal vein after passing through a series of capillaries. In cold perfusion vessels with a diameter larger than 0.3 mm must be treated individually. The obvious temperature change in the larger vessels will bring in the displacement causing by the thermal contraction. This paper is dedicated to present a comprehensive investigation on the thermal effects of larger blood vessels during cold perfusion including temperature change and corresponding heat stress. A structural model of heat transfer in kidney is developed using currently available anatomical and physiological data. To characterize the effect of thermally significant blood vessels on heat transfer inside the tissues during cold perfusion, the cryoprotectant in the blood vessel was controlled by the energy equation and Navier-Stokes equations. The tiny capillaries and its surrounding biological tissue were treated as the porous media following Darcy's Law. The controlling equations were numerically solved by CFD software. The numerical simulation for the coupled transient thermal field and stress field is carried out by sequentially thermal-structural coupled method based on ANSYS to evaluate the stress fields and of deformations which are established in the blood vessel and tissue. The results indicated that the thermal effects of large blood vessels could remarkably affect the temperature distribution of cold perfusion. And the heat stress obvious changed during cooling, especially for the vein. The maximal heat stress occurred at the export of the vein. This position may be the keys to avoid stress injury during perfusion. This paper provides a guideline to optimize the cold perfusion process from the biomechanics effect.
