Evaporation-limited capillary flow in a heated microchannel.

Capillary flow in porous media is significant in several applications including medical diagnosis, environmental monitoring and food safety analysis. Porous hydrophilic wicks such as textiles, paper, metallic weaves, and textured substrates are used in thermal management and desalination systems, leveraging their capillary action to efficiently manage liquid flow and heat transfer. Here, we study wicking and evaporation characteristics of a volatile liquid to maximize the rate of evaporation in a microchannel. Coupled equations of mass and energy conservation are solved in a microchannel to evaluate the equilibrium wicking length at different applied heat flux. We investigate the role of geometric parameters and heat flux on the wicking length. Wicking length combined with the width of the channel forms the evaporating surface area, increase in which increases the evaporation rate. At low heat flux, the wicking length is observed to decrease monotonically with an increase of the channel width. At high heat flux, an optimum width is obtained for which the equilibrium wicking length is the highest. Correspondingly, a set of geometric parameters, comprising of the width and depth of the channel is obtained for a given heat flux, which can serve as design criteria for evaporators to achieve high evaporation rate in phase change applications.