Experimental study of productivity progress for a solar still integrated with parabolic trough collectors with a phase change material in the receiver evacuated tubes and in the still

This study aimed to improve the productivity of conventional single slope solar still by integrating the evacuated tube on the focusing axis of a parabolic trough collector (PTC) and a heat exchanger serpentine with an under basin phase change material (PCM). The PCM served as a latent heat storage material within the evacuated tube's inner pipe. The PTC had a rim angle of 80 degrees, an aperture width of 0.9 m, and a length of 3 m. In the proposed solar still, the working fluid that was circulated around the serpentine heat exchanger and the evacuated tube includes water, oil, and nano-oil (mineral oil, 3% CuO by volume concentration) operated at different flow rates of 0.5, 1.0, and 1.5 L/min. For comparison, the performances of the improved and traditional solar stills were evaluated during the three summer months of June, July, and August 2019, under the weather conditions of Ismailia, Egypt. Moreover, the effect of the saline water depths of 1.5 and 3 cm in the solar still basin was investigated. The results show that the daily productivity for the conventional solar still and oil as a working fluid at the flow rates of 1.5, 1.0, and 0.5 L/min, and nano-oil as a working fluid at the flow rate of 0.5 L/min were 3.182, 4.67, 6.21, 8.79, and 11.14 L/m(2)/day while the efficiency of the system were 28%, 13.7%, 18%, 26%, and 34%, respectively, at the saline water depth of 1.5 cm. The cost per distillate liter for the traditional and improved (case 3 with the nano-oil) solar stills was 0.02 and 0.0154 $/L, respectively.