Enhanced heat transfer using metal foam liquid supply layers for micro heat spreaders

We propose a nanostructured metal foam liquid supply layer that can efficiently provide operating fluid to evaporator hot spots and can be easily integrated within micro heat spreaders. The liquid supply layer is incorporated onto the micropost evaporator wicks to enhance the capillary performance by combining the high permeability of liquid supply layers and the high capillary pressure of micropost wicks. The coverage ratio (CR) between the liquid supply layer and the evaporator wicks was varied from 15% to 100% to find the proper CR for efficiently increasing the liquid supply performance with minimizing the parasitic thermal resistance. By incorporating the liquid supply layer of CR 33% onto the Cu micropost wicks of ∼0.4 solid fraction, the results show that a high (>6 W/cm2 K) and stable heat transfer coefficient can be achieve at a high heat flux range (>400 W/cm2), which outweighs the performance of previously-reported evaporator wicks. The achieved maximum heat flux was over 150% higher than the same wicks without the liquid supply layer. Our work shows the importance of the efficient liquid supply to hot spots and provides the strategy to increase the heat transfer performance at high heat flux region. The suggested liquid supply layer will help develop micro heat spreaders for the thermal management of high power density microprocessors, IGBTs and thermophotovoltaic cells.