Model optimization of dry-out heat flux from micropillar wick structures

Capillary-driven thin film evaporation in wick structures is promising for thermal management of high-power electronics because it harnesses the latent heat of evaporation without the use of an external pumping power. The complexities associated with liquid-vapor interface and liquid flow through the wick structures, however, make it challenging to optimize the wick structure geometries to boost the dry-out heat flux. In this work, we developed a numerical model to predict the dry-out heat flux of thin film evaporation from micropillar array wick structures. The model simulates liquid velocity, pressure, meniscus curvature and contact angle along the length of the wick surface through conservation of mass, momentum and energy, based on a finite volume approach. In particular, we captured the three-dimensional meniscus shape, which varies along the wicking direction, by solving the Young-Laplace equation. We determined the dry-out heat flux upon the condition that the minimum contact angle on the micropillar surface reaches the receding contact angle. With this model, we calculated the dry-out heat flux as a function of micropillar structure geometries (diameter, pitch and height), and optimized the geometry to maximize the dry-out heat flux. Our model provides an understanding of the role of the wick structures in capillary-driven thin film evaporation and offers important design guidelines for thermal management of high-performance electronic devices.