ON THE EFFECT OF POROUS LAYERS ON MELTING HEAT-TRANSFER IN AN ENCLOSURE

An experimental study is reported of melting of a pure substance in a vertical rectangular enclosure that is partially occupied by horizontal or vertical layers of a relatively high thermal conductivity porous medium. To enhance heat transfer, the porous layers are located in regions where the melting rates for a pure substance are the lowest. n-Octadecane is used as the phase-change material, and the porous matrix is composed of glass or aluminum beads of various diameters. Natural convection in the liquid and conduction in the solid are present. The temperature distributions in both the fluid and porous regions are measured using thermocouple rakes, and solid-liquid interface positions and shapes are recorded by tracing the interface at specified time intervals. It is found that the differences in the thermophysical properties between the porous layer and the pure fluid layer cause strong variations in heat transfer, melt convection, and the movement and shape of the solid-liquid interface. Although a porous layer may cause a faster movement of the solid-liquid interface, the melting and heat transfer rates are reduced compared to the case without a porous layer. This is attributed to the effects of the low porosity and permeability of the porous media tested, which are not offset by the high thermal conductivity of the media. Considerable care must be exercised in trying to enhance melting heat transfer using high thermal conductivity porous media.