Experimental Study of Backward Conduction in Multi-Microchannel Heat Sink

In this paper, the effect of conjugate phenomenon on the heat transfer in microchannel heat sinks is experimentally investigated. Circular channels, 18 in number, each having length of (40 ± 0.4) mm and diameter of (400 ± 09) μm were fabricated in rectangular metallic plates. The plates of three different materials, i.e., copper, brass and stainless steel, were used to prepare the heat sinks. Water and ethanol were used as coolants. Heat input during the experimentation ranged from 3 to 25 W. Maranzana number, M, the measure of conjugate phenomenon, was observed to vary from 0.015 to 2.60 in the range of flow rates considered for the coolants. Rise in temperature of the fluid at inlet location was observed under every experimental condition. Under constant heat flux conditions, the temperature of the fluid at the entrance increased up to 20 °C for the conditions indicating extreme values of the parameter ‘M.’ The maximum value of Nusselt number determined from the experimental data was observed to be smaller (2.78) than those from the expected (4.36) for circular channels. This difference is attributed to the phenomenon of longitudinal conduction in microchannels. A correlation for heat transfer in microchannels is suggested taking into account the effect of longitudinal conduction. Regression analysis for the correlation indicated good agreement between the dependent and independent variables.