An experimental and theoretical investigation of a wick-type solar still for water desalination

Abstract

Solar distillation using a wick-type solar still was investigated theoretically and experimentally. A tilled flat plate wick-type solar still was designed and constructed. Charcoal cloth was used as an absorber/evaporator material and for saline water transport. A theoretical model for the performance of the wick-type solar still has been developed and analysed. It investigates the effect of various factors on the still productivity. A Fortran computer program has been developed and a finite difference technique was used to solve the main equations and to determine related parameters. Indoor experimental testing was carried out to investigate the effect of input water flow rate and salinity on the still productivity together with the variation of the solar still efficiency with absorber temperature. The tests were conducted using the irradiance from a lamp array. Outdoor testing was carried out with and without a V-trough solar concentrator on clear days in summer and winter. Representative daily efficiencies of the still with and without the solar concentrator were about 60% and 50% respectively on clear days in summer. The solar absorptances of samples of charcoal cloth and blackened hessian cloth were determined before and after environmental exposure. The solar reflectances of samples of 3M Scotchcal Films and aluminised plastic (as potential reflecting materials for the concentrator mirrors) were investigated before and after environmental exposure and also exposure to elevated temperatures and humidities. It has been concluded that: charcoal cloth is a good material for use as an absorber/evaporator and also as a water transport medium. Increase of the input water mass flow rate leads to a reduction in the efficiency of the wick-type solar still. The still efficiency decreased linearly with Increase of salinity of the input saline water. The productivity of the still Increases linearly with absorber temperature. The best absorber-cover separation Is found to be in the range 20-25 mm. Wind speed has no significant effect (up to about 10 m/s) on the performance of a well sealed still. The transmittance of the glass cover has a strong influence on the still efficiency. Use of the solar concentrator with the inclined wick-type solar still leads to a greater fractional increase In still productivity on clear days in winter than on clear days in summer.