Simultaneous prediction of dryout heat flux and local temperature for thin film evaporation in micropillar wicks

Porous wicks are of great interest in thermal management because they are capable of passively supplying liquid for thin film evaporation, a promising method to reliably dissipate heat in high performance electronics. While dryout heat flux has been well-characterized for many wick configurations, key design information is missing as many previous models cannot determine the distribution of evaporator surface temperature. Temperature gradients are inherent to the passive capillary pumping mechanism since the shape of the liquid/vapor interface is a function of the local liquid pressure, causing spatial variation of permeability and heat transfer coefficient (HTC). Here, we present a comprehensive modeling framework for thin film evaporation in micropillar wicks that can predict dryout heat flux and local temperature simultaneously. Our numerical approach captures the effect of varying interfacial curvature across the micropillar evaporator to determine the spatial distributions of temperature and heat flux. Heat transfer and capillary flow in the wick are coupled in a computationally efficient manner via incorporation of parametric studies to relate geometry and interface shape to local permeability and HTC. This model predicts notable variations of HTC (similar to 30%) across the micropillar wick, highlighting the significant effects of interfacial curvature. Further, we are able to quantify the tradeoff associated with enhancing either dry out heat flux or HTC by optimizing geometry. Our model provides all of the information needed to guide the design and optimization of micropillar wicks by resolving evaporator temperature distributions in addition to dryout heat flux. (C) 2019 Published by Elsevier Ltd.