Water extraction from the atmosphere

Abstract

This investigation is driven by the desire to find an alternative method of obtaining fresh water. More specifically, fresh water is to be obtained by condensation of atmospheric water vapor on a surface maintained below the dew point by a radiative heat loss from its surface to the night sky. To properly simulate the condensation process, an accurate estimation of the effective sky temperature is required. To estimate the effective night sky temperature an experimental system, consisting of a series of metal plates embedded on a heat transfer panel, a weather station and a control system, was built. The temperature of each plate was controlled using an electric flat-plate heater. A control loop was implemented to ensure that the heat transfer panel was adjusted automatically to always be oriented perpendicular to the wind direction. In addition to the effective night sky temperature, the experimental system was designed to estimate the convective heat transfer coefficient between the plates and ambient air as well as the surface emissivity of the plates. The results obtained from theoretical analyses and preliminary experiments are presented and discussed. Special emphasis was given to mathematical solution of the system of equations that need to be solved to obtain the effective sky temperature. It was shown that, although the solution of the system of equations was straightforward for the direct heat transfer problem, there was a serious difficulty to solve the inverse heat transfer problem to retrieve the desired parameters.