Experimental comparative study on a solar still combined with evacuated tubes and a heat exchanger at different water depths

The low freshwater output is always a matter of concern regarding a solar still. It is observed from the current literature that evacuated tubes are directly connected to the still basin for productivity enhancement. The main limitation of integrating evacuated tubes directly to solar still is rapid scaling on the inner surfaces of tubes due to the presence of dissolved impurities in water. This increases thermal resistance and decreases the overall performance of the still. In the present experimental study, a copper tube heat exchanger is installed in still basin and waste engine oil is utilised as a working fluid in the evacuated tube collector (ETC) and heat exchanger circuit. This modification increases the evaporation rate of basin water and boosts freshwater output. The modified still is experimentally investigated at distinct water depths of 4 cm, 5 cm and 6 cm, and the performance is simultaneously compared with a conventional still. Experimental results showed maximum daily productivity of 7.38 L/m(2) day and daily efficiency of 30.5% achieved for modified still at 4 cm water depth. These values are 138.9% and 2.1% higher than that of conventional still respectively at same water depth.