Experimental characterization of the effects of geometric parameters on evaporative pumping

This study is interested in determining the experimental relation between the suction pressure and evaporation rate from the upper surface of a flat, thin porous membrane, which naturally draws water from a reservoir, and its microchannel feeding system. The effects of three main design parameters of a water delivery system on the evaporation rate of the membrane are considered: (i) the diameter of the microchannels irrigating the membrane, (ii) the length of the irrigating microchannels, and (iii) the surface area of the membrane. Additionally, we also evaluated the effect of the pumping height (i.e., the vertical distance between the membrane and the main reservoir) on the evaporation rates for the three design parameters. While the maximum evaporation rate from the membrane is a function of the membrane's properties (e.g., permeability and porosity), as well as the ambient conditions (e.g., temperature, pressure and humidity), this study focused on determining the geometric parameters of closed water-feeding microchannels that properly hydrate a porous membrane while not impeding evaporation. Results indicated that the evaporation rate was mostly unaffected by the channel dimensions considered. Moreover, evaporation rates increased with increasing surface area (between 20.3 cm2 and 176.7 cm2) but at a decreasing rate of return. Finally, the suction pressures achieved were inversely related to hydrodynamic pressure drop and were unaffected by the membrane diameter.