The thermal and hydrodynamic performance of passive two-phase cooling devices such as heat pipes and vapor chambers is limited by the capabilities of the capillary wick structures employed. The desired char- acteristics of wick microstructures are high permeability, high wicking capability and large extended meniscus area that sustains thin-film evaporation. Choices of scale and porosity of wick structures lead to trade-offs between the desired characteristics. In the present work, models are developed to predict the capillary pressure, permeability and thin-film evaporation rates of various micropillared geometries. Novel wicking geometries such as conical and pyramidal pillars on a surface are proposed which provide high permeability, good thermal contact with the substrate and large thin-film evaporation rates. A com- parison between three different micropillared geometries – cylindrical, conical and pyramidal – is pre- sented and compared to the performance of conventional sintered particle wicks. The employment of micropillared wick structure leads to a 10-fold enhancement in the maximum heat transport capability of the device. The present work also demonstrates a basis for reverse-engineering wick microstructures that can provide superior performance in phase-change cooling devices.


heat pipe, thermal spreaders, wick structure, evaporation, micro-pillars

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R. Ranjan, A. Patel, S. V. Garimella and J. Y. Murthy, “Wicking and Thermal Characteristics of Micropillared Structures for use in Passive Heat Spreaders," International Journal of Heat and Mass Transfer Vol. 55, pp. 586–596, 2012.