Optimization of Square and Circular Ammonia-cooled Microchannel Heat Sink with Genetic Algorithm

Minimization of the thermal resistance and pressure drop of a microchannel heat sink is desirable for effective heat removal which is becoming a serious challenge due to the continuous miniaturization of such cooling systems with increasing high heat generation rate. Optimization of the hydraulic diameter and wall width to channel width ratio of square and circular microchannels to minimize the two objective functions was completed with the multi-objective genetic algorithm (MOGA). Environmentally friendly liquid ammonia was used as the coolant and the thermophysical properties have been obtained based on the average experimental saturation temperatures measured along an ammonia-cooled 3.0 mm internal diameter horizontal microchannel rig. The optimized results showed that with the same hydraulic diameter and pumping power, circular microchannels have lower thermal resistance. Based on the same number of microchannels per square cm, the thermal resistance for the circular channels is lower by 21% at the lowest pumping power and lower by 35% at the highest pumping power than the thermal resistance for the square microchannels. Results obtained at 10 °C and 5 °C showed no significant difference probably due to the slight difference in properties at these temperatures.