NATURAL-CONVECTION IN A SQUARE ENCLOSURE HEATED PERIODICALLY FROM PART OF THE BOTTOM WALL

Transient heat transfer by laminar natural convection in a square cavi ty partially heated from below is studied numerically using a finite d ifference procedure. The temperature of the heating element is uniform , but its magnitude varies sinusoidally with time, oscillating about a fired mean value. The opposite cold wall is maintained at a constant temperature, while the rest of the bottom wall and the vertical walls are adiabatic. The transient solutions obtained are all periodic in ti me (0.02 less than or equal to tau less than or equal to infinity). Pa rameters of the problem are the enclosure aspect ratio (A = 1), dimens ionless length of the heating element (0.125 less than or equal to B l ess than or equal to 0.5), position of the heating element (0 less tha n or equal to epsilon less than or equal to 0.25), dimensionless ampli tude of the heating element temperature (0 less than or equal to a les s than or equal to 0.4), Prandtl number (Pr = 0.72), and Rayleigh numb er (10(5) less than or equal to Ra less than or equal to 2 x 10(6)). H eat transfer and effects of various parameters on the flow and tempera ture fields are studied.