Natural convection heat transfer in a horizontal porous enclosure with high porosity

Shiina, Yasuaki; Ishikawa, Kota*; Hishida, Makoto*

Heat transfer characteristics near the critical Rayleigh number for the onset of natural convection of horizontal anisotropic porous fluid layer heated from below with thin cylindrical rods inserted with high porosity above 0.822 to unity were studied by an analysis and an experiment. The critical Rayleigh number and dependence of Nusselt number on the Rayleigh number were analysed by linear stability theory and series expansion method on the basis of Darcy flow assumption. Critical Rayleigh number, increased with decrease in the porosity, was higher for the experiment than for the analysis but the difference was decreased with decrease in Darcy number. Experimental Nusselt number was considerably decreased with decrease in the porosity near unity although is rather same as the case of Benard convection without cylindrical rods. The experimental Nusselt number can be expressed by one correlation curve when Nusselt number is plotted against Darcy number of the present experiment was rather large to satisfy Darcy flow assumption. Experiment shows that Darcy flow assumption will be satisfied for Darcy number.