NONLINEAR FORCED CONVECTIVE HEAT TRANSFER IN A COMPOSITE AIR/POROUS LAYER WITH PERMEABLE TOP AND BOTTOM BOUNDARIES AND ENERGY SOURCE: DIFFERENT PENETRATION DEPTH OF PATTERNS

Abstract

This paper deals with nonlinear convective heat transfer in a composite heat-generating air/porous system bounded by the top and bottom solid permeable planes of equal temperature and forced by a vertical throughflow. In the presence of a uniform energy source, penetrative convection originates over this throughflow. It is numerically simulated by the finite difference method and Newton's method. The paper extends previous studies by considering the evolution of the supercritical and subcritical nonlinear convective patterns of a different penetration depth, increasing the supercriticality <i>r</i> from 0 to 2, Pèclet number Pefrom - 6 to 5, and depth ratio <i>d</i> from 0.05 to 0.20. The convection together with the basic throughflow contributes to the total heat transfer rate and improves thermal performance of the partial porous system. The case can find its application, for example, in storing the biologically active plant products releasing heat. The short-wave convection localized in the upper air layer appears over the upward throughflow with Pe > 0. Its relative contribution to the total heat flux is much smaller than that of the basic throughflow and decreases with increases in the values of Pe and <i>d</i>. Both local and large-scale convective patterns can initiate over the downward throughflow with Pe < 0. Their relative contributions to the total heat flux grow with increasing the absolute values of Pe and <i>d</i>. The large-scale convection that covers the air and porous layers at Pe = -6, <i>d </i>= 0.05 enhances heat transfer more effectively than does the local one occurring within the air layer.