Experimental study of the liquid/vapor phase change in a porous media of two-phase heat transfer devices

Highlights: • A 75% reduction in the hydrostatic head decreases the casing temperature by 25%. • A 300% increase in the hydrostatic head reduces the heat transfer coefficient by 27%. • Vapor pocket increases with the adverse hydrostatic head. • Effect of the wick material on heat transfer is important. The study presents an experimental examination of heat and mass transfer with phase change in a porous media composed of copper foam. The aim of the study involves separately examining the effect of the adverse hydrostatic head, subcooling at the wick inlet and wick properties (porosity and average pore diameter) on the heat and mass transfer inside porous media. The experimental results indicate that an increase in the adverse hydrostatic head from $\Delta h=0.5$ cm to $\Delta h=2$ cm increases the casing temperature of 5 °C for low heat loads and 40 °C for high heat loads owing the vapor breakthrough toward the wick inlet. The results also suggest that the heat transfer coefficient and the critical heat flux are reduced by approximately 27% (for a heat load of 106 W) and 17%, respectively for the same adverse hydrostatic head variation. The increase in the subcooling at the wick inlet reduces the thermal performance of the evaporator. With respect to wick property effects, the results indicate that the porosity and average pore diameter significantly impact the phase change phenomenon inside the porous wick and the casing temperature. There are optimal values of porosity and average pore diameter leading to the best thermal performance of the capillary evaporator.