EXPERIMENTAL ESTIMATION OF THE PHASE FRONT UNDER LOCAL THERMAL NON-EQUILIBRIUM CONDITION ― PHASE CHANGE PHENOMENA IN POROUS MEDIA

摘要

A systematic experimental method of estimating the extent of the phase front under local thermal non-equilibrium condition in porous media saturated with phase change material has been developed. During phase change in porous medium, the solid matrix and the pore material are under thermodynamic non-equilibrium condition until the phase change process is complete. It is often hypothesized that the solid matrix and the pore material are in local thermal equilibrium (LTE) condition hence, the arrival of the phase front is predicted based on this hypothesis. An understanding of the rate of freezing and thawing in a porous medium undergoing the phase change process is important to permit proper implementation of procedures such as cryopreservation, cryosurgery, and to predict the thermal performance of passive cooling systems for electronic devices, In this paper, a systematic method of estimating the extent of the phase change front is developed. Results show that during the phase change process the porous medium is far from local thermal equilibrium condition.