Unsteady mixed convection in a horizontal channel with protruding heated blocks and a rectangular vortex promoter

The objective of this research is to study the resonance cooling enhancement in electronic systems. The unsteady mixed convection through a horizontal channel with two isolated protruding blocks on the bottom wall has been studied numerically. For this geometry, at moderate Reynolds number, the flow is found to separate at the leading edge of the first block, and then reattach at the top surface of the second block. The reattachment length behind the last block increases with the buoyancy level, indicated by Gr/Re ², where Gr is the Grashof number, while the critical Re, at which the flow becomes unstable, decreases. Tatsutani et al. (1993) found three distinct flow patterns in the forced channel flow with a pair of square cylinders located in tandem. In the present research, if buoyancy effects are excluded, the flow is more stable because of the stabilization due to the bottom wall. When Re exceeds a critical value, vortex is shed only from the second block, and rolls over the bottom wall with its size decaying, while one or two recirculating cells are trapped in the groove. The base vortex shedding frequency is dependent more strongly on the geometry of the channel than on Re. The critical value of Re is much lower when perturbation is introduced by a rectangular or square promoter in the channel. The frequency and amplitude of perturbation are changed by adjusting the geometry of the promoter. When the perturbation frequency increases, a shorter time is available for the boundary layer to develop over the top surfaces. This results in a thinner boundary layer and improves the heat transfer. However, the situation along the groove is different. An improved fluid exchange between the main flow and the recirculating cell occurs when the promoter is employed. The effects of frequency and perturbation amplitude on the heat transfer are investigated. The study consists of three parts. The first studies the developing flow in the grooved channel; the second investigates the vortex shedding from a rectangular promoter confined in a smooth channel; and the last studies the effect of resonance by tuning the frequency of vortex shedding.