The test days for the first and second experimental scenarios was starting from 7:00 am till 7:00 pm, Fig. 6 depicts the hourly variation of ambient temperature and solar intensity. The solar intensity of the two test days (19-08-2020 and 20-08-2020) is almost identical, which increases until it reaches to the maximum value at noon, then dramatically decreases until it reaches its lowest value near sunset. Also, the highest recorded ambient temperature was recorded between 1:00 pm and 5:00 pm. This means that all cases of CHSS, HSS-IRM, HSS-IRAF, HSS-IRM & SG, and HSS-IRAF & SG can be compared to one another because all was exposed to very similar ambient climate conditions, allowing for a more accurate comparison.
Fig. 7 shows the influences of utilizing the internal reflective, as well as, the internal reflective and the El-Oued sand grains on basin saltwater temperature of the distillers from 7:00 am to 7:00 pm on August 19, and 20, 2020. The highest basin saltwater temperature was recorded for utilization of the internal reflective mirrors and the El-Oued sand grains (HSS-IRM & SG). The maximum recorded basin saltwater temperature was reached to 68, 72, 74, 78, and 80 oC for CHSS, HSS-IRAF, HSS-IRM, HSS-IRAF & SG, and HSS-IRM & SG respectively, between 2:00 pm and 3:00 pm. This because that the increases the intensity of absorbed solar rays filling on the basin saltwater for utilization internal reflective mirrors, as well as, use El-Oued sand grains as energy store material. Fig. 8 shows glass cover temperature of different distillers (CHSS, HSS-IRAF, HSS-IRM, HSS-IRAF & SG, and HSS-IRM & SG) through the period 7:00 am to 7:00 pm on August 2020.
In the solar distillers, the convection heat transfer represents the main driven in the distillation field. Whereas, the temperature difference between the saltwater and glass (Tw-Tg) is a measure of natural buoyancy inside solar distillers. With increasing the temperature difference, the buoyancy force will be increases, and thus will be improving the rate of distillate production inside the hemispherical solar distillers. Figure 9 shows the variations of the temperature difference (Tw-Tg) within the different cases of hemispherical distillers (CHSS, HSS-IRM, HSS-IRAF, HSS-IRM & SG, and HSS-IRAF & SG). As shown in Fig. 9, in the reference case (CHSS) the temperature difference ranged between 1–19 oC, while the use of internal reflective aluminum foil (HSS-IRAF) increases this difference to 1-23oC, with the average improvement of 25.8%. While the use of internal reflective mirrors (HSS-IRM) increases this difference to 1-24oC, with the average improvement of 48.1%. While the use of internal reflective aluminum foil and El-Oued sand grains (HSS-IRAF & SG) increases this difference to 1-26oC, with the average improvement of 61.9%. While the use of internal reflective mirrors and El-Oued sand grains (HSS-IRM & SG) increases this difference to 1-28oC, with the average improvement of 83.8%. The results of temperature analysis evident that the use of internal reflective mirrors and El-Oued sand grains (HSS-IRM & SG) represent the good obtain to achieves the highest distillate production of hemispherical solar distiller.
Based on the recorded data of the hourly distillate production of the different cases of hemispherical distillers presented in Fig. 10, its found that the hourly distillate production has the same trend for CHSS, HSS-IRM, HSS-IRAF, HSS-IRM & SG, and HSS-IRAF & SG, but with the higher rates for utilizing of the internal reflective mirrors and El-Oued sand grains (HSS-IRM & SG). The recorded peak hourly distillate production which reached 750, 800, 900, 1100, and 1150 mL/m2 h for CHSS, HSS-IRM, HSS-IRAF, HSS-IRM & SG, and HSS-IRAF & SG respectively was recorded within the period 2:00 pm till 3:00 pm. It is evident from this that the use of internal reflective mirrors and El-Oued sand grains (HSS-IRM & SG) represent the good option to achieves the highest instantaneous distillate production of hemispherical solar distillers.
To get the influences of the internal reflective and the El-Oued sand grains on cumulative distillate production of the hemispherical distillers, Fig. 11 shows cumulative distillate production of five hemispherical solar distillers (CHSS, HSS-IRAF, HSS-IRM, HSS-IRAF & SG, and HSS-IRM & SG). As presented in Fig. 11, the cumulative distillate production of reference unit (CHSS) reached 4750 mL/m2, while use of internal reflective aluminum foil (HSS-IRAF) increases the cumulative distillate production to 6200 mL/m2 day, with the improvement of 30.5%. While the use of internal reflective mirrors (HSS-IRM) increases the cumulative distillate production to 7150 mL/m2 day, with an improvement of 50.5%. While the use of internal reflective aluminum foil and El-Oued sand grains (HSS-IRAF & SG) increases the cumulative distillate production to 8350 mL/m2 day, with an improvement of 75.8%. While the use of internal reflective mirrors and El-Oued sand grains (HSS-IRM & SG) increases the cumulative distillate production to 9400 mL/m2 day, with an improvement of 98%. The results concluded that the utilization of internal reflective mirrors and El-Oued sand grains (HSS-IRM & SG) represent the optimal design configuration to achieve the highest cumulative distillate production of hemispherical solar distillers.
Figure 12 shown the exergy efficiency and daily thermal efficiency CHSS, HSS-IRAF, HSS-IRM, HSS-IRAF & SG, and HSS-IRM & SG. As shown the exergy efficiency and thermal efficiency of the reference distiller (CHSS) reached 2.2% and 38.9%, respectively. While the use of internal reflective aluminum foil (HSS-IRAF) increases the exergy and thermal efficiencies to 3.44% and 50.65%, respectively. While the use of internal reflective mirrors (HSS-IRM) increases the exergy and thermal efficiencies to 4.4% and 58.3%, respectively. While the use of internal reflective aluminum foil and El-Oued sand grains (HSS-IRAF & SG) increases the exergy and thermal efficiencies to 5.4% and 67.9%, respectively. While the use of internal reflective mirrors and El-Oued sand grains (HSS-IRM & SG) increases the exergy and thermal efficiencies to 6.62% and 76.3%, respectively.
Figure 13 shows the influences of the utilization of the internal reflective, as well as, internal reflective and El-Oued sand grains on hemispherical distillers performance improvement. The results presented that the maximum improvement in cumulative distillate production, exergy efficiency, and thermal efficiency was recorded for utilization of internal reflective mirrors and El-Oued sand grains (HSS-IRM & SG) which reached 98, 200.9, and 96%, respectively, compared to reference case (CHSS). This is mainly because of the higher reflectivity of the mirrors utilized in this empirically work as well as the good thermal properties of El-Oued sand grains, and then utilization of both internal reflective mirrors and El-Oued sand grains (HSS-IRM & SG) together represent the good options to achieves a highest hemispherical distillers performances.
Comparison of present study with published similar works
In Table 3, we compared our results with published similar works. Through the results, compared to the reference distiller (CHSS), it has been noted that the yield of hemispherical solar still containing internal reflective aluminum foil sheets (HSS-IRA) increases by 30.5%, the yield of hemispherical still containing reflective mirrors (HSS-IRM) increases by 50.5%, the yield of hemispherical still containing internal reflective aluminum foil sheets and El-Oued sand grains (HSS-IRAF & SG) increases by 75.8%, the cumulative yield of hemispherical solar still containing internal reflective mirrors and El-Oued sand grains increases by 98%. From Table 3, it can be noticed that the productivity of "V" type SS with mirror [28] is minimum with a value equal to 11.92%. However, for the single slope SS with reflective glass mirror, it is maximum with a value equal to 75% [22].
Table 3
Comparison of improvement rates of distillate production of previously published works and our experimental work
Author name
|
Classification
|
Modifications
|
Gain in distillate production (%)
|
Our results
|
Hemispherical SS
|
- Internal reflective aluminum foil
- Internal reflective mirrors
- Internal reflective aluminum foil and El-Oued sand grains
- Internal reflective mirrors and El-Oued sand grains
|
30.5
50.5
75.8
98
|
Chandrika et al. (2021)
|
Single slope SS
|
- Reflective glass mirror
- Reflective aluminum foil sheet
|
68.57
48.57
|
Attia et al. (2021d)
|
Hemispherical SS
|
− 10 g/L of Phosphate granules
− 20 g/L of Phosphate granules
|
33.7
47.9
|
Attia et al. (2021e)
|
Single slope SS
|
- Bed Phosphate granules
|
16.8
|
Kumar et al. (2008)
|
“V” type SS
|
- Mirror
- Mirror and charcoal
|
11.92
14.11
|