Evaporative heat transfer in a capillary structure heated by a grooved block

Experimental results of capillary-driven heat and mass transfer in a vertical rectangular capillary porous structure, heated from a grooved block placed on the top, are reported in this paper. The formation of the liquid-vapor menisci in the vicinity of the downward-facing heated surface provided the capillary-force for the upflow of water in the porous structure. The temperature distributions in both the heating block and porous structure, as well as the induced mass flow rate of water, were measured under different heat flux conditions. The experimental results show that with an increase of the imposed heat flux, the heat transfer coefficient increases to a maximum value and then decreases afterward. It is also found that the liquid-vapor interface moved toward the downward-facing heated surface as the imposed heat flux was increased. The heat transfer mechanisms leading to the maximum heat transfer coefficient and the critical heat nux are explained based on the visual observation of the phase-change behavior and the measured temperature distributions within the porous structure. The effects of particle sizes, the inlet temperature of the subcooled liquid, and the adverse gravity force on the heat transfer characteristics are also examined.