Experimental and numerical study of mixed convection heat transfer in a vented cavity partially filled with a porous medium: Effects of reynolds and rayleigh numbers on Nusselt number and flow regimes

This article presents a comprehensive investigation of mixed convection flow and heat transfer within a vented, partially side-heated cubical cavity, incorporating a porous medium with low-conductivity square-shaped inclusions. The study encompasses an extensive range of Rayleigh numbers (10(6) < Ra < 6 x 10(6)) and Reynolds numbers (200 < Re < 4000) while maintaining a fixed Prandtl number of Pr = 0.71. This investigation spans over three decades in Richardson numbers (Ri = Ra/(Re-2 Pr)), aiming to discern the interplay between the Nusselt number, Nu, and the Richardson number. Our understanding of Nusselt number dependencies is enhanced by combining PIV measurements of heat transfer and velocity fields with temperature field data. The study uses both experimental and numerical PIV data, incorporating porous media representation to reveal heat transfer scaling with both Reynolds and Rayleigh numbers. Computational Fluid Dynamics (CFD) methods are used to explore the complex physical behavior under different flow conditions. Three distinct flow and heat transfer regimes have been identified, predicated upon the Richardson number. For Ri < 25, the flow structure and Nusselt number exhibit similarities with pure forced convection, where the Nusselt number scales as Nu similar to Re-0.6, independent of the Rayleigh number. Conversely, for Ri > 70, natural convection dominates the vicinity of the heating wall, rendering the Nusselt number less sensitive to Reynolds number variations and predominantly dictated by the Rayleigh number. Notably, the intermediate regime, ranging from 25 < Ri < 70, witnesses a competition between upward-directed natural convection flow at the heating wall and downward-directed forced flow, culminating in a minimum effective Nusselt number.