An asymmetrical vapor chamber with multiscale micro/nanostructured surfaces

A novel asymmetrical vapor chamber, patterned with multiscale micro/nanostructured surfaces was studied experimentally. This kind of micro/nanostructured evaporator and condenser surfaces on one hand improves the capillary capability of the wick, provides more nucleation sites and increases the heat transfer area. On the other hand, it results in drop-wise condensation which has a much higher heat transfer coefficient compared with film condensation. Furthermore, it also provides a shortcut for the condensate to drop back directly to the evaporator. Thus, smaller liquid flow resistance and high anti-dryout capability are achieved. As a result, both the critical heat flux (CUP) and heat transfer coefficient (HTC) can be enhanced. In order to study the effects of different working fluids, an amount of ethanol was mixed in the deionized water as the working fluid. The ratio of the ethanol to the mixture of DI water and ethanol varied from 0% to 80%. The effects of the acoustic excitation on the asymmetrical vapor chamber were also studied by attaching a Piezoelectric actuator on the bottom surface of the evaporator. It was found that the thermal resistance of the vapor chamber with micro/nanostructured evaporator was much lower than that of vapor chamber with bare sintered wick. The existence of the ethanol would deteriorate the performance of the asymmetrical vapor chamber. The performance of the asymmetrical vapor chamber would be enhanced by acoustic excitation, because the acoustic excitation will accelerate the departure of the bubble from the porous wick. (C) 2014 Elsevier Ltd. All rights reserved.