Abstract: “In this paper we examine the thermal-convective stability of a fluid-saturated porous medium filled within a vertical cylindrical container heated from below. The upper and lower surfaces of the cylinder are impermeable and are kept at constant but different temperatures. The lateral sidewall is impermeable and subject to mixed heating which is characterized by the Biot number. The threshold of Rayleigh number, above which the small disturbance becomes unstable, is sought from the characteristic equation. Our results show that the preferred mode at onset is always axisymmetric for all aspect ratios when Biot number approaches infinitely, and it becomes non-monotonic variation with respect to aspect ratio when Biot number is finite.”

Keywords: thermal convection, porous medium, Newtonian heating, cylindrical container, Biot number.