The freshwater yield is the main goal of hemispherical distillers. This output is determined by the amount at which saline water evaporates and the rate at which evaporated water vapor condenses. The evaporation rate increases with argument saltwater temperature and temperature difference between saltwater and internal glass [3][4]. Furthermore, increasing temperature differential between internal glass and external glass, the temperature difference between ambient air and external glass, and increasing outside wind speed all enhance the condensation rate[5][6]. As a result, evaluating the still temperatures provides a clear picture of the still performance.
4.1. Hemispherical Solar Still temperatures
Figures 4, 5, 6, and 7 illustrates the temperature variations with time of the proposed hemispherical solar Distillers components and the corresponding ambient temperature and solar rays within tested days. Figure 4 introduces the changes in temperature throughout time of saline water, internal glass, external glass, and ambient of Hemispherical Solar Distiller with Truncated Circular Cone-Shaped Reflector Mirrors (HSD-TCC-RM) at inclination angles of 10 and 15 degrees (with vertical) compared with Traditional Hemispherical Solar Distiller (THSD). However, all these temperature variations of HSD-TCC-RM20 and HSD-TCC-RM25 in comparison to THSD are presented in figure 5. Furthermore, figure 6 illustrate the temperature gradients of HSD-TCC-RM30 and HSD-TCC-RM35 components contrasted with THSD. Additionally, the changes of temperature with time of HSD-TCC-RM40 and HSD-TCC-RM45 main parts and its difference with traditional solar still temperatures are displayed in figure 7.
As indicated from these figures (4:7), the solar intensity profile has the same trend during all tested days and its values have nearly the same values during the four days. This is because the cases studied were performed within four successive days in the period between 5/8/2021 and 8/8/2021 to avoid any variations in ambient conditions. It is clear from figures (4:7) that solar intensity values have a small value at the sunrise and rises gradually until it reaches its maximum value at noon time and then its values decline with time to hit the lowest value at the end of daytime. However, the solar intensity gets its maximum value at 12pm, it is noticed that the maximum values of all components for the proposed systems were obtained three hours later at 15pm. The reason of this time delay is that heat transferred through the solar radiation needs time to be absorbed by the hemispherical solar still components and to get warmer. Furthermore, it is obvious that the saline water temperatures for all studied cases have the maximum values, followed by the internal glass temperatures, and then the external glass temperatures which are always higher than the ambient temperatures. The reason of this is that the solar rays is transmitted through a still glass and absorbed by still absorber which in contact with saltwater. Then, the water is heated and evaporated. The water vapor is condensed on the internal surface of the glass.
Figure 4 demonstrates the water, internal glass, external glass, and ambient temperature variation over time for HSD-TCC-RM10, and HSD-TCC-RM15 compared with traditional hemispherical solar distiller (THSD). It is illustrated from figure 4 that the internal glass temperatures for any system is higher than the corresponding values of external glass temperatures due to the thermal resistance of glass and the latent heat of condensing absorbed by internal glass surface. It is revealed that using truncated circular cone-shaped reflector mirrors (TCC-RM) with an inclination angle of 10o has a negative effect on the water temperature values. However, using the TCC-RM with 15o enhanced the maximum water temperature by 2.78% compared with THSD due to increasing the incident solar radiation on HSS area.
The effect of using TCC-RM with inclination angles of 20, and 25 angles on the temperatures of HSD is introduced in figure 5. Results in figure 5 reveals that using TCC-RM20, and TCC-RM25 improves the maximum water temperature of THSD by 2.78%, and 5.56%, respectively. The maximum difference in temperature between saltwater and internal glass of THSD, HSD-TCC-RM20, and HSD-TCC-RM25 systems were 12, 14, and 15 degrees, respectively. That means that the evaporation rate of HSD-TCC-RM25 is higher than HSD-TCC-RM20, followed by traditional solar distiller (THSD). Furthermore, it is noticed from figure 5 that the maximum temperature difference between internal and external glass of THSD, HSD-TCC-RM20, and HSD-TCC-RM25 systems were 6, 6, and 7 degrees, respectively. This interprets that HSD-TCC-RM with 25o inclination angle has the maximum condensation rate compared with other corresponding systems.
Figure 6 demonstrates the effect of utilizing ERM with inclination angles of 30, and 35 degrees on THSD temperatures. It is concluded that using TCC-RM30 and TCC-RM35 argument the maximum water temperature of traditional THSD by 4.23%, and 2.82%, respectively. THSD, HSD-TCC-RM30, and HSD-TCC-RM35 systems have maximum temperature differences of 12, 13, and 12 degrees, respectively, between water and internal glass. That results in HSD-TCC-RM30 achieved more evaporation rate of water vapor compared with HSD-TCC-RM35 and THSD systems. However, when comparing findings in previous figures (4, 5, and 6), it is clear that HSD-TCC-RM25 has a maximum saltwater temperature (76oC), and a maximum difference in temperature between saltwater and internal glass (15oC) compared with other mentioned systems.
The impact of using TCC-RM with inclination angles of 40, and 45 degrees on traditional THSD temperatures is shown in Figure 7. It can be concluded from figure 7 that utilizing TCC-RM with 45o inclination angle has a negative impact on the water temperature compared with conventional distiller. The maximum water temperatures obtained from THSD, HSD-TCC-RM40, and HSD-TCC-RM45 were 71, 71, and 69oC, respectively.
By comparing the temperatures of all proposed systems in figures (4, 5, 6, and 7), it is revealed that an optimal inclination of TCC-RM is 25o which result in a maximum water temperature of 76oC, and maximum difference in temperature between saltwater and internal glass (15oC) compared with all other proposed systems. Which means that HSD-TCC-RM25 has the maximum evaporation rate, and then maximum freshwater productivity.
4.2. Hemispherical Solar Distillers Freshwater Yield
Figure 8 depicts the effect of adjusting the inclination angle of the truncated circular cone-shaped reflector mirrors (TCC-RM) with the hemispherical sola distiller on the hourly yield. The hourly productivity of the traditional (THSD) and the hemispherical solar distiller with truncated circular cone-shaped reflector mirrors (HSD-TCC-RM) at various inclination angles are shown in this graph. Figure 8 depicts that the hourly production rises progressively from a morning until reaches to maximum value on 14:00 PM, which corresponds to nearly the time of maximum temperature as previously stated due to increased solar irradiation. After that, as the solar intensity diminishes, the amount of freshwater produced decreases till the end of day. Figure 8 indicates that using TCC-RM with 25o, and 30o inclination angle achieve the maximum hourly yield of 1.1 litter/h for each system, followed by HSD-TCC-RM20, and HSD-TCC-RM35 with 1 litter/h compared with 0.85 litter/h for THSD. Findings reveal that using TCC-RM with 15o, 40o inclination angle improves the maximum hourly productivity by 5.88%, and 11.76% relative to THSD, respectively. On the contrary, adjusting the inclination angle of TCC-RM at 10o, and 45o effects negatively on the hourly yield of the still in comparison with traditional THSD.
Figure 9 shows how, till the sunset, the accumulated freshwater yield for all proposed solar stills grows. Furthermore, it is resulted that using truncated circular cone-shaped reflector mirrors with an inclination angle of 15, 20, 25, 30, 35, and 40 degrees enhanced the accumulated freshwater productivity of the traditional THSD by 12.82%, 20.51%, 42.74%, 35.04%, 24.79%, and 14.02%, respectively. However, the total accumulated yield of HSD-TCC-RM10, and HSD-TCC-RM45 declined by 11.97%, and 6.84%, respectively relative to THSD system. Also, Table 2 shows the influences of utilization the truncated circular cone-shaped reflector mirrors with an inclination angle on the percentage improvement in cumulative yield of hemispherical solar distillers.
From the findings presented in figure 9, all studied hemispherical solar still systems can be put in descending order as follow: HSD-TCC-RM25, HSD-TCC-RM30, HSD-TCC-RM35, HSD-TCC-RM20, HSD-TCC-RM40, HSD-TCC-RM15, THSD, HSD-TCC-RM45, and HSD-TCC-RM10. As a result, it is concluded that the optimum inclination angle for the truncated circular cone-shaped reflector mirrors used with hemispherical solar distiller is 25o, which achieves the maximum accumulated freshwater yield between all other HSS proposed systems.
Table 2
The improvement in cumulative yield at different inclination angles of TCC-RM.
Date of experiment
|
THSD
|
HSD-TCC-RM
|
Truncated circular cone-shaped reflector mirrors inclination angle θ (°)
|
10
|
15
|
20
|
25
|
30
|
35
|
40
|
45
|
05-08-2021
|
5.85
|
5.15
|
6.60
|
-
|
-
|
-
|
-
|
-
|
-
|
06-08-2021
|
5.85
|
-
|
-
|
7.05
|
8.35
|
-
|
-
|
-
|
-
|
07-08-2021
|
5.85
|
-
|
-
|
-
|
-
|
7.90
|
7.30
|
-
|
-
|
08-08-2021
|
5.85
|
-
|
-
|
-
|
-
|
-
|
-
|
6.67
|
5.45
|
Improvement (%)
|
-
|
11.97
|
12.82
|
20.51
|
42.74
|
35.04
|
24.79
|
14.02
|
-6.84
|