TRANSIENT NATURAL CONVECTION IN A SQUARE ENCLOSURE WITH HORIZONTAL WALLS SUBMITTED TO PERIODIC TEMPERATURES

Abstract

Natural convection in a square cavity with its horizontal walls submitted to different heating models has been investigated by a finite difference procedure. The hot temperature of the bottom surface varies sinusoidally with time, while that of the opposite surface (cold temperature) is maintained constant or varied sinusoidally. The vertical walls are considered adiabatic. Parameters of the problem are the amplitude of the variable temperature(s) (0 a 0.5), its (their) period (0.001 tau 1), the dephasing between hot and cold temperatures (phi = 0 and pi), the Rayleigh number (5 x 10⁵ Ra 10⁶) and the Prandtl number (Pr = 0.72). The effect of these parameters on heat transfer and fluid flow within the cavity is studied. The results obtained show that the heat transfer can be enhanced or reduced, with respect to the case of constant temperatures, by proper choice of the variable heating mode, the parameters related to the periodic temperature(s), and the Rayleigh number. By varying the two imposed temperatures, fundamental differences have been observed comparatively with the case of variable hot temperature and that of constant thermal boundary conditions.