The purpose of this investigation was to study the simultaneous mass and heat transfer mechanism in evaporation through a porous membrane with a non-wettable surface. Such water repellent membranes permit the passage of water vapor, but not liquid water. The investigation concerned the mass transfer rate through the membrane pores with flow on one or both sides of the membrane. The water-repellent membrane separated a hot salt solution from the fresh water, and a copper sheet separated the fresh water from a cold salt solution. A three-channel evaporator-condenser was used, and the membrane consisted of glass fiber paper treated with a teflon dispersion. The temperature range studied was from 93 to 190⁰F. A temperature difference and a corresponding vapor pressure difference maintained across the membrane provided the driving force both for mass and heat transfer through the membrane and heat recovered through the copper sheet to cold salt solution. Theoretical and empirical correlations were employed to fit the experimental data. It was observed that heat transfer resistance and diffusion in the membrane pores were the major resistances to total mass transfer. The correlation predicted rates of mass transfer resistance close to the experimental values. The heat transfer coefficient was affected by the mass diffusion. The ratio of heat transfer coefficient with diffusion to that without diffusion was 1.5, and was slightly dependent on flow. The mass transfer coefficient varied form 0.22 to 0.516 lb/(hr)(ft²)(in-Hg). The overall heat transfer coefficient for the membrane varied from 48 to 104 BTU/(hr(ft²)(⁰F), and the overall heat transfer coefficient for the copper sheet varied from 54 to 84 BTU/(hr)(ft²)(⁰F) --Abstract, page ii-iii
