Revisit on the natural convection from horizontal multi-channel rectangular-fin heat sinks

Abstract

Unsteady numerical analysis is conducted for horizontal 16-channel rectangular-fin heat sinks with heat sink length of L = 127 mm. Beside normal heat sinks, those with guard-fin blocks at both sides as in the experiments of Harahap and McManus (1967) and Harahap and Setio (2001) are also studied to clarify the effects of guard-fin blocks on the flow characteristics and heat transfer performance as compared to normal heat sinks. The inner channels of a normal heat sink with low fins of H = 6.4 mm exhibit moderate sliding oscillatory motions in both directions along and normal to the channel, due to strong interaction between the end flow and the side flow. The outer channels are obviously suppressed by the side flow. The guard-fin blocks can relieve the side-flow suppression on the outer channels of the low-fin heat sink. The average heat transfer coefficients for the fin channels are higher than those of normal heat sinks by about 20%. For a high-fin heat sink with H = 25 mm, the plume velocity increases due to stronger buoyancy so that the end-flow is dominant, and the plume appears to be a weakly oscillating single-chimney flow. The guard-fin blocks are of little effect for high-fin heat sinks. The traditional explanation for lower h‾s of sliding-chimney flow in that the low-pressure middle recirculation region draws in warmer air from above is shown to be incorrect when the cool side flow is involved. The reason for low h‾s is mainly because the low-h recirculation region in the middle of the heat sink is broader for a sliding-chimney flow.