Improving the performance of a hybrid solar desalination system under various operating conditions

Abstract

The issue of freshwater shortage is a general problem that touches almost all human beings, and everyone is trying to find creative and practical solutions to try to overcome this problem. In this paper, the proposed desalination system consists of a modified solar still (MSS), parabolic trough solar collector (PTSC), separation unit (SU), and two external condensers (EC). The idea of this proposed device is that the PTSC was utilized to heat the saline feed water to a temperature from which steam can be extracted, and then a separation is made for this steam from the remaining water that has risen in temperature and has not been evaporated to be used as feed water for MSS. Also, MSS has been modified by making all its walls (except for the back wall of the distiller) of glass to obtain a greater amount of absorbed solar radiation. Besides, a double glass cover for MSS was used instead of the single glass sheet to prevent the heat loss to the atmosphere through the glass cover. The double glass cover is two sheets of glass between which there is a slight vacuum pressure. Regarding the experimental tests conducted through July 2021, the main conclusions of this work can be pointed. It was revealed that at 12:00, the maximum water temperature of PTSC was 55 °C at 20 L/hr (0.33 L/min), where the solar radiation was 1050 W/m². Besides, the effectiveness of PTSC was 60%, and the total accumulated productivity of PTSC was 83 L/daytime (daytime = 9 hrs). Moreover, the total accumulated productivities of conventional solar still (CSS) and MSS with double glass cover were 3330 and 2325 mL/m².daytime, respectively. Therefore, the productivity of MSS with double glass cover was smaller than that of the CSS by about 30%. In addition, the total accumulated freshwater distillate of CSS and MSS with double glass and condenser was 3370 mL/m².daytime and 6150 mL/m².daytime, respectively. As a consequence, the productivity of MSS with double glass and condenser was more than that of CSS by around 82.50%. In addition, the thermal and exergy efficiencies were 31% and 2.54%, respectively for CSS and 47.5% and 3.95%, respectively for MSS with double glass and condenser. Besides, the total productivity of the hybrid system (PTSC and MSS together) was reported as 91.0 L/daytime. Also, the cost of distilled water of proposed hybrid system is 0.008 $/L, and payback period of costs on proposed system is three months. Moreover, the environmental parameters of EPF, ϕCO2, and Z′ for MSS are slightly more than the double of that for CSS.