Numerical study if natural convection in an enclosure with protruding and flush heat sources

Abstract

Numerical investigations have been performed on an incompressible fluid contained in a two dimensional enclosure. Five identical heat sources were mounted on one vertical wall of the enclosure with uniform vertical spacing. Two different types of heat sources i.e. protruding and flush were studied ..The vertical wall opposite to the heated sections and the bottom wall were adiabatic. The top surface of the test enclosure was an isothermal heat sink.. The horizontal and vertical dimensions of the protruding heaters were Lg = 9 mrn and L1 = 15 mrn respectively. The vertical spacing between the heaters was Lz = 15 mill. For flush heater Lg = o mrn. Investigations were performed with different values of cavity width, resulting in the variation of aspect ratio (height-ta-width ratio) and cavity width -to-protruding heater height ratios of 3.67 to 9.17 and 2.0 to 5.0, respectively. The effect of variation of heat flux from the heat sources, resulting in variation of modified Rayleigh numbers ranging from 1.9 x 106 to 4.9 x 1010 was studied. The investigations were performed with ethylene glycol as the working fluid. The governing transport equations for turbulent flow under investigation are closed using the two equation model of turbulence (k-E), which includes gravity-density interaction. The equations are discretised using a finite volume technique. A non-uniform grid arrangement of 62 X 62 was used. The governing equations were solved incorporating the Pressure Implicit with Splitting of Operators (PISO) method. Results indicate that heat transfer and fluid motion within the enclosure are influenced by the Rayleigh number, aspect ratio and heat input. At larger width (W=45 & 36mrn) a single vortex is observed occupying the flow domain and at smaller width (W=22.5 & 18 mrn) the single vortex structure disintegrates and several secondary flow cells appear within it. Increase in the width results in a decrease in the difference between the temperatures of the top heated sections. The temperature gradient in the core flow region are found to be considerably small. The correlation of local Nusselt number versus local modified Rayleigh number is independent of the number of heaters in the vertical array and vertical height location of the heaters. The results show reasonably good agreement with the experimental data.