Experiments on the transient heat transfer of minichannel heat sink under high heat flux density in an enclosed loop

The experiments are carried out to study the transient heat transfer characteristics of a minichannel heat sink under high heat flux density that varies from 150 W/cm(2) to 200 W/cm(2), in an enclosed loop. The heat flux is supplied by the ethyne flame. The average rate of the cooling water is from 1.00 m/s to 1.86 m/s. The temperature rise of the heated surface and the temperature rise of the cooling water are measured. The results show that the temperature rise of the heated top surface rises quickly at the startup period of heating, and then increases slowly. The variation of the top surface temperature is similar to the voltage in the RC circuit. The surface temperature is a function of thermal resistance and thermal capacity of the heat sink. The temperature of the cooling water at outlet also rises quickly at the startup period of heating, and then becomes stable. The temperature increases are related to the heat flux density and the rate of the cooling water. There is a time delay between the temperature rise of the inlet cooling water and the startup of heating. This delay is related to the length of the enclosed loop and the rate of the cooling water. The pressure drop across the heat sink decreases slightly with time at high heat flux since the water viscosity reduces with the increasing temperature. (C) 2010 Elsevier Inc. All rights reserved.