ENHANCED BOILING HEAT-TRANSFER IN POROUS LAYERS WITH APPLICATION TO ELECTRONIC-COMPONENT COOLING

The present contribution deals with a continuous approach to modeling steady state evaporative heat transfer and vapor/liquid counterflow in porous media, in an attempt o identify the mechanisms responsible for the observed heat transfer enhancement during boiling of liquid coola nts in porous layers. A 1-D computer code is developed solving the mas s, momentum and energy conservation equations for a bottom and/or volu metrically heated, capillary porous medium. The limitations of such a macroscopic study are recognized and relate mainly to its inability to provide an insight of the micromechanics aspects at the pore level. N evertheless, the macroscopic calculations are employed to highlight th e effects of the relevant parameters (fluid properties, medium permeab ility and porosity, thermal conductivity of solid matrix, layer thickn ess) and identify the relative significance of the different mechanism s (capillarity, counterflow, phase change). A simplified analytical ap proach is taken to describe the steady state thermohydraulic behaviour of a liquid saturated porous medium, This offers a fast, approximate method for predicting the limiting dryout heat flux in the porous laye r. Qualitative agreement is obtained when the theoretical reproduction of the experimental boiling curves is attempted. Based on the underst anding gained, investigations are underway to suggest geometric and th ermal modifications of the system which may contribute to a significan t increase of the heat flux removed in the case of electronic componen ts cooling.