To Obtain the best modifications for CHSS, HSS-N, and HSS-C that achieve the highest productivity with the lower inexpensive. The comparison was achieved in the same climate to ensure that the three solar stills were exposed to the same solar radiation at the same time. This similarity in operational conditions makes the comparison more accurate. Experiments were carried out from 8.00 AM to 6.00 PM. Figure 3 shows the solar radiation (W/m2) in 6, 7, and 8 Oct. 2020. Solar radiation intensity increases from morning to reach maximum between 12.00 and 13.00 and decreases till vanishes at nearly 18.00 (sunset). Maximum solar radiation was 1007 W/m2. The three solar stills under study were exposed to the same solar radiation at the same time. Also, as presented in Fig. 4 the temperature of ambient air in the test location along the working period from 8.00 AM to 6.00 PM was various between 28–44 oC, 29–44 oC, and 28–44 oC on 6, 7, and 8 Oct. 2020, respectively.
The basin water (or nanofluid) temperature versus time on 6, 7, and 8 Oct. 2020 was shown in Fig. 5 (a, b, and c) for the three different configurations of solar distillers under study. This figure shows that basin water (or nanofluid) temperature increases gradually from morning (nearly ambient temperature) till reaching a maximum within the period 1:00 PM till 3:00 PM with a delay about one hour from the peak of solar radiation. Also, this figure shows that the trend of basin water temperature for CHSS and HSS-C is almost the same and have the same values, but by add CuO nanoparticles to basin water (CuO-water nanofluid) in HSS-N, the basin temperatures will be increased with a ratio depends on the concentrations of CuO nanoparticles in nanofluid. Where the average improvement in the basin nanofluid temperature for HSS-N by adding CuO nanoparticles reached 4.7%, 9%, and 12.7% for CuO nanoparticles concentrations 0.1, 0.2, and 0.3% respectively as compared to CHSS and HSS-C. Basin water temperatures for CHSS and HSS-C are very close to each other or nearly the same. This told that cover cooling has no effect on the basin water temperature while adding CuO increases it. As the nanoparticle concentration increases, water basin temperature increases due to absorptivity increasing, and then the generation rate of water vapor inside the basin increases with the increase in the concentrations of CuO nanoparticles.
Figure 6 shows the variation of outside glass cover temperature of CHSS, HSS-N, and HSS-C in 6, 7, and 8 Oct. 2020. This figure shows that outside glass cover temperature increases gradually from morning (nearly ambient temperature) till reaching a maximum within the period 1:00 PM till 3:00 PM and starts to decrease again after this period. The outside glass cover temperatures for CHSS and HSS-N are very close to each other or nearly the same. This told that adding the CuO nanoparticles to basin water in HSS-N has no effect on the basin temperature while adding glass cover cooling technology in HSS-C decreases it. Where the average reduction in the outside glass cover temperature for HSS-C by adding the water film glass cover cooling technology reached 11.4%, 13%, and 17.8% for cooling-water flow rate 1.5, 2, and 2.5 L/h, respectively as compared to CHSS and HSS-N. For HSS-C, a cooling water flow rate of 2.5 L/h has the lowest glass temperature, this lower in outside glass cover temperature will increase the water vapor condensation rate.
Figure 7 shows the hourly variation of distillate yield for CHSS, HSS-N, and HSS-C through the operation time from 8:00 AM to 6:00 PM on 6, 7, and 8 Oct. 2020. As shown in this figure, in all operating conditions, distillate water increases gradually till reaching maximum at 2:00 PM with about two-hour delay from maximum radiation intensity. The maximum hourly distillate yield for CHSS reached 600 mL/m2 h at 2:00 PM, while the maximum hourly distillate yield for utilization HSS-N improved to 850, 950, and 1000 mL/m2 h at 2:00 PM for CuO-water nanofluid concentration 0.1, 0.2, and 0.3%, respectively. Also, for HSS-C, the maximum hourly distillate yield reached 750, 800, and 850 mL/m2 h at 2:00 PM for cooling-water flow rates of 1.5, 2, and 2.5 L/h, respectively. Based on the analysis of hourly distillate yield for CHSS, HSS-N, and HSS-C, it is recommended that utilized the modified HSS-N (0.3% volume fraction) to achieving the highest hourly distillate yield produced from the hemispherical solar distillers.
Fig. 8 presents the accumulative distillate yield for the three models CHSS, HSS-C, and HSS-N from 8:00 AM to 6:00 PM for 6th, 7th, and 8th Oct. 2020. As presented in Fig. 8, the average daily accumulative yield of CHSS is 3.85 L/m2/day, while the daily accumulative yield of HSS-N increases to 5.75, 6.40, and 6.80 L/m2/day with improvement 49.3, 66.2, and 76.6% at volume fraction 0.1, 0.2, and 0.3%, respectively. Also, the daily accumulative yield of HSS-C increases to 4.9, 5.35, and 5.7 L/m2/day with improvements of 27.3, 39, and 48% at water film flow rates of 1.5, 2, and 2.5 L/h, respectively. Also, Fig. 9 shows a comparison between the accumulative distillate yield for the three models CHSS, HSS-C with three different flow rates (1.5, 2, and 2.5 L/h), and HSS-N with three different concentrations of CuO-water nanofluid (0.1, 0.2, and 0.3%). Based on the accumulative distillate yield analyzes presented in Figs. 8 and 9, it is recommended that utilized the modified HSS-N (0.3% volume fraction) to achieving the highest accumulative distillate yield.