Productivity enhancement of solar stills by nano-coating of condensing surface

Wettability is one of the most important factors which significantly influences solar still efficiency. Moreover, it determines the condensation mode, i.e., filmwise or dropwise condensation. In the present study, materials with different wettability were applied as the condensing surface to evaluate the effect of wettability on the distillate production of a single slope solar still. To compare the effects of dropwise and filmwise condensation on the condensate yield, the wettability of the condensing surface was changed by applying a nano-silicon solution according to a dip coating technique. All the experiments were conducted at three surface inclination angles. The results revealed that the nano-coating changed the condensation mechanism from filmwise to dropwise for all the materials. Also, it was concluded that dropwise condensation leads to increased condensate production at higher surface inclination angles. For example, condensate production of a glass surface was increased by 23% after nano-coating at a surface inclination angle of 50 degrees. In addition, the amount of dripping was estimated before and after the coating process by using additional collectors. To illustrate, the amount of dipping from uncoated aluminium surface was 106 ml which increased to 198 ml after the coating process at a surface inclination angle of 30 degrees.