Characterization of capillary performance of composite wicks for two-phase heat transfer devices

A composite wick by covering a layer of sintered copper powder on micro V-grooves was developed for two-phase heat transfer devices. Capillary performance of the composite wicks, which integrates both permeability and capillary pressure, was experimentally examined by comparing with normal sintered and grooved wicks. Forced liquid flow tests with deionized water were conducted to determine the permeability. Using a novel infrared (IR) thermal imaging method, the capillary rate-of-rise tests with ethanol were carried out to characterize the capillary performance of wicks. Two kinds of powder with spherical and irregular shapes, and four different particle size of <50, 50-75, 75-110 and 110-150 μm were evaluated for the purpose of design optimization. Tests results show that the composite wicks enhanced both the permeability and capillary performance compared to the sintered wicks, and exhibited much larger capillary pressure than the grooved wicks. The permeability and capillary performance of composite wicks increased monotonically with the powder size, whereas the capillary pressure did not follow this order. The feasibility of the well-known Washburn's equation in characterizing the capillary rate-or-rise processes was also assessed.