Solidification of a superheated fluid in a porous medium: effects of convection

The solidification of a superheated fluid-porous medium contained in a rect angular cavity is studied numerically. The bottom and side walls of the cav ity are insulated while the top wall is maintained at a constant temperatur e below the freezing Point of the saturating fluid. The study is focused on the effects of superheat on the development of natural convection and heat transfer during the solidification process. For a fluid initially at a tem perature above the freezing point, the results obtained by neglecting conve ction overpredicts the solidification time by about 12 percent for a Raylei gh number of 800. When convection is taken into account, it is found that t he solidification process consists of three distinct regimes: the conductio n regime, convection regime, and the solidification of the remaining fluid that can be described by the Neumann solution for the solidification of a f luid at its freezing point. The numerical simulations are based on the Darc y-Boussinesq equations, using the front tracking method in a transformed co ordinate system. The entire solidification process is described in terms of the evolutions of the streamlines and isotherm patterns, the maximum and a verage temperatures of thr fluid, the interface position, and the heat tran sfer rate The parametric domain covered by these simulations is 0 less than or equal to Ra less than or equal to 800, 0 less than or equal to St(l) le ss than or equal to 0.67, St(s) = 0.3 and XL = 1 where Ra is the Rayleigh n umber, St(l) the liquid Stefan number ST the solid Stefan number and XL the aspect ratio of the cavity.