Pool boiling heat transfer and simplified one-dimensional model for prediction on coated porous surfaces with vapor channels

Boiling heat transfer on porous coated surfaces with vapor channels was investigated experimentally to determine the effects of the size and density of the vapor channels on the boiling heat transfer. Observations showed that bubbles escaping from the channels enhanced the heat transfer. Three regimes were identified: liquid flooding, bubbles in the channel, and dry-out. The heat transfer coefficient and q̇cr of the porous surfaces with vapor channels were much higher than those on the smooth surface. The maximum heat transfer occurred for an optimum vapor channel density and the boiling heat transfer performance was improved if the channels were open. According to observations, vapor could escape through the vapor channel while liquid was sucked by a porous structure, and hence, the two-phase region will extend to a pool liquid at a given flux. This indicates that capillarity plays a great effect on the boiling and the heat transfer performance can be increased significantly. A simplified one-dimensional formulation for the two-phase flow within such a heterogenous structure was proposed using an equivalent dual porous model. It is demonstrated theoretically that the geometric dimensions and the density of vapor channels affect the boiling heat transfer. This may provide a new key for enhancing boiling heat transfer by capillary porous structure.