The cooling techniques of the solar stills' glass covers – A review

The productivity of a solar still is influenced by the temperature difference between condensing and evaporating areas. Previous researches determined that increasing the difference between water–glass temperatures enhances the daily productivity of solar stills. To maintain this temperature difference high, fans, condensers, storing materials, reflectors, and the glass cover cooling were utilized. Continuous supply of air or water film over the glass cover leads to diminish the temperature of glass. Also, the cooling water film performs the important role of continuous self-cleaning of the glass cover. The presence of filth and dirt on the glass cover greatly diminishes the efficiency of still. Continuous cleaning of the glass cover keeps high levels of efficacy. In this regard, this paper aims to review the various methods of glass cover cooling used to enhance the performance of the solar stills. The cooling of glass covers is found to achieve a reduction in glass cover temperature in the range of 6–20 °C with an improvement in stills efficiency and productivity up to 15.5% and 20% maximum, respectively. It was concluded that for the tubular solar still with cooling air flow of glass cover, the daily productivity improved by approximately 32.8%, and improved by approximately 59% with cooling water flow more than the still without cooling.