Non-conventional solar stills Part 2. Non-conventional solar stills with energy storage element Original Research Article

A novel continuous single-stage solar still that makes use of a phase change energy storage mixture (PCESM) for promoting energy usage has been devised and constructed. The still consists of a module made from an external body of galvanized iron, a frame of galvanized iron, a pan at the bottom of the still for encapsulating the PCESM, an aluminum reservoir for saline water, a copper channel for the collected distilled water and a glass cover that is inclined at a small angle to the horizontal, for trapping solar radiation. The design makes use of the latent heat of fusion of the PCESM that is placed in the lower pan for effecting continued desalination even after sunset, and beneath which a pad of sawdust functions as insulation. The optimum PCESM was precisely an emulsion of paraffin wax, paraffin oil and water in a specific ratio to which aluminum turnings were added to assist in heat transfer by conduction. Factors such as concentration and flow rate of saline water, type of energy storage material and inlet water temperature were investigated for their effect on the still productivity. Results indicated that the use of an energy storage material led to a larger productivity of distilled water and that the larger the concentration of the saline water the lower the productivity of the still. Also higher flowrate and high inlet saline water temperature improved the still efficiency. The maximum productivity of the still was 4.536 L/m2 in 6 h daytime operation plus overnight distillation due to stored energy, when the saline water flowrate was 40 ml/min, equivalent to a still efficiency of 36.2%.