The current investigation aimed to augment the distilled water production of the hemispherical solar distiller by implementing flat and v-corrugated iron trays absorber basins. To fulfill the optimal modification that reaches the maximum freshwater productivity, the experiments were carried out under the outdoors desert conditions of El-Oued (33°27′N, 7°11′E), Algeria in two typically consecutive days in October 2021 based on two experimental manners. In the 1st manner, the effects of using flat and v-corrugated iron trays absorber basins on the performance of hemispherical distillers were studied. Wherefore, three solar distillers were fabricated and examined; namely, conventional hemispherical solar distiller (CHSD), hemispherical solar distillery with V-corrugated iron trays (HSD-VIT), and hemispherical solar distiller with flat iron trays (HSD-FIT). In the 2nd manner, the impacts of utilizing flat and v-corrugated iron trays with wick materials on hemispherical still performances were investigated. Hence, a double wick layer was added in the basin of HSD-FIT and HSD-VIT in the 2nd testing manner, where the 2nd distiller became a hemispherical solar distiller with flat iron trays and wick materials (HSD-FIT & WM), and the 3rd still became a hemispherical solar distiller with v-corrugated iron trays and wick materials (HSD-VIR & WM).
Figure 3 displays the hourly fluctuation of total solar intensity and weather temperature as a function of local time for two of the typical test days for the two experimental sceneries of the proposed hemispherical distillers in October 2021 (07-10-2021 & 08-10-2021) from 8:00 a.m. to 6:00 p.m. It can be observed in Fig. 3 that the trends of solar irradiance within the two experimented days are the same which increments gradually to the maximum value in midday's and slightly reduces till afternoon time. It is recorded that the average and maximum solar intensity values are found to be 619.3 and 1006.0 W/m2, respectively. While the averagely and maximal ambient temperatures are recorded to be 38.2 and 44.0 oC, respectively.
The thermal performance of HSD-VIT and HSD-FIT have been examined with and without using wick materials (WM) and compared with CHSD. The measured values for basin water temperature of the five studied distillers (HSD-VIR&WM, HSD-FIT&WM, HSD-VIT, HSD-FIT, and CHSD) at constant saline water level (1.50 cm) are presented in Fig. 4. It indicates that HSD-VIR&WM has the maximal saline water temperatures, followed by HSD-FIT&WM, HSD-VIT, and HSD-FIT, respectively, whereas the CHSD has the minimal saline water temperatures. It is found that the water temperatures of the basin for HSD-VIR&WM, HSD-FIT&WM, HSD-VIT, and HSD-FIT show about 0 – 8°C, 0 – 6°C, 0 – 5°C, and 0 – 2°C greater than that for CHSD, respectively. The significant increase in water basin temperature of the HSD-VIR&WM compared to the CHSD is due to the combined utilization of v-corrugated iron trays and wicks with the absorber basin, which remarkably maximized the vaporization surface area and thus, the condensation and evaporation rates in HSD-VIR&WM were higher than that of CHSD, especially that the temperatures of glass cover were almost the same for the HSD-VIR&WM and the CHSD. It is found that the mean and maximum water temperatures of the HSD-VIR&WM are recorded to be 69.0 and 59.2 oC, respectively, whereas they are obtained to be 61.0 and 51.54 oC, respectively, for the CHSD.
Figure 5 illustrates the hourly fluctuation of the temperature of exterior and interior cover surfaces of the hemispherical still under the diverse modified cases (HSD-VIT&WM, HSD-FIT&WM, HSD-VIT, HSD-FIT, and CHSD). It is obvious that the temperatures of the inner surface of the glass cover surface are higher than that of the outer cover surface, as a result of the distilled content collected on the inner surface of the glass casing of the distiller. Also, as shown in Fig. 5, the HSD-VIR&WM indicated a higher glass temperature than CHSD by about 0 – 1.0°C. The increment in the cover temperature of the HSD-VIR&WM is due to higher condensation and vaporization rates than CHSD as a result of a larger vaporization area for HSD-VIR&WM. The difference between the interior surfaces temperatures of the glass of all studied solar stills was about 0.0–1.5°C.
The diurnal changes in hourly freshwater productivity for all investigated cases of hemispherical distillers (HSD-VIT&WM, HSD-FIT&WM, HSD-VIT, HSD-FIT, and CHSD) at a saline water depth of 1.5 cm inside the distillers are displayed in Fig. 6. As respected, it is clear that at all times the HSD-VIT&WM inhibited the highest distilled water productivities, followed by HSD-FIT&WM, HSD-VIT, and HSD-FIT, respectively, whereas the lowest distilled water productivities are obtained by the CHSD. The latter result is due to that the use of v-corrugated iron trays basin in the HSD-VIR&WM remarkably increased the saline water temperature and thus augmented the rates of distilled vapor generation and freshwater productivities as a result of the larger vaporization area for HSD-VIR&WM. Besides the utilization of wick materials acts as a thermal moderator by further increasing the water heating in the v-corrugated iron trays basin by the heat energy transferred by radiation and convection from the pores of wick materials. Figure 5 indicates that the hourly output freshwater had low values in the morning at the outset of the solar distiller and progressively increases with time attaining maximal productivity midday, and afterward it gradually decreases till late evening. The experimental findings unveiled that the hourly distillate was maximum at 02:00 pm, where it was recorded to be 1.0, 0.95, 0.85, 0.65, and 0.60 kg/m2.h for HSD-VIT&WM, HSD-FIT&WM, HSD-VIT, HSD-FIT, and CHSD, respectively.
Figure 7 demonstrates the accumulative amounts of freshwater for the five investigated cases of hemispherical solar distillers. It is obvious from Fig. 7 that the v-corrugated basin hemispherical solar distiller embedded with iron trays and wick materials outperformed the best accumulative productivity compared with other modifications of hemispherical distiller arrangements and traditional hemispherical distiller, for the same above-previously mentioned reasons. The maximum accumulated water distillate was found to be 7.05 kg/m2.d, for the HSD-VIT&WM, while the corresponding for the HSD-FIT&WM, HSD-VIT, HSD-FIT, and CHSD were about 5.95, 5.50, 4.40, and 3.85 kg/m2.d, respectively. This refers to that the total accumulative productivity of modified hemispherical distiller with v-corrugated iron trays and wicks are enhanced by 83.12% more than that for CHSD.
The performance of the five investigated hemispherical distillers has been compared and assessed in terms of the daily energy efficiency and total distillate production and of the distiller. The daily efficiency of the still η, is a vital parameter to figure out the actual improvement in the performance of solar distiller from the perspective of the total energy received by the distiller. It accounts on the entirety of hourly yield Σmw, latent heat of the vaporization hl, daily solar intensity Σ Is(t), and surface area of the basin As, as described in the following equation;
$$\eta =\frac{{\sum {{h_l} \times {m_w}} }}{{\sum {{A_s} \times I(t) \times 3600} }}$$
1
Figure 8 demonstrates a bar chart of the total cumulative yield and daily thermal efficiency along with their amelioration percentages for the four modified hemispherical distillers (HSD-VIT&WM, HSD-FIT&WM, HSD-VIT, and HSD-FIT) compared to the CHSD. It is reported that the HSD-VIT&WM, HSD-FIT&WM, HSD-VIT, and HSD-FIT obtained an enhancement in the total cumulative yield of 83.12% (7.05 kg/m2.day), 54.55% (5.95 kg/m2.day), 42.85% (5.50 kg/m2.day), and 14.30% (4.40 kg/m2.day), respectively, over the CHSD at a constant saltwater deepness of 1.5 cm over day cycle. Moreover, the daily efficiency of CHSD, HSD-FIT, HSD-VIT, HSDFITWM, and HSDVITWM has been computed to be 33.94, 38.72, 48.28, 52.16, and 61.67%, respectively. It is obviously confirmed that employing flat iron trays and v-corrugated iron trays improves the daily efficiency of the hemispherical distiller by about 14.06 and 42.23%, respectively, over that of CHSD. While, the addition of wick materials to the flat iron trays and v-corrugated iron trays further enhances the daily efficiency of the hemispherical distiller by about 53.66 and 81.68%, respectively, over that of CHSD. Accordingly, the latter results inferred that the amalgamation between two those efficacious modifications (v-corrugated iron trays and wick materials) regards as the best choice among the different investigated modifications for augmenting the freshwater productivity and daily efficiency of the hemispherical solar distillers.
Comparison with other published designs of solar stills
To clarifier the significance of utilizing the proposed V-corrugated iron trays and wick materials in ameliorating the performance of solar stills. A comparison between the results of recent work with these of other relevant studies established in solar stills has been demonstrated in Table 2. The obtained enhancements in both daily efficiency ad total water production exhibited a good performance compared to those revealed by other previous works.
Table 2
Comparison between the results of the current work and previous relevant studies in performance improvement of solar distillers.
Ref
|
Design of solar distiller
|
Additives and modifications
|
Daily productivity (kg/m2.day)
|
Daily
Eff.
(%)
|
Productivity increase
(%)
|
Kabeel et al., (2018b)
|
Single slope solar distiller
|
Jute cloth wicks mixed with sand
|
5.90
|
56.0
|
18.0
|
Sharshir et al., (2020a)
|
Single slope solar distiller
|
Copper absorber with wicks and copper chips
|
6.30
|
60.9
|
62.30
|
Sharshir et al., (2020b)
|
Stepped double slope distiller
|
Carbon black nanoparticles and linen wicks
|
4.46
|
60.2
|
80.5
|
Shalaby et al., (2016)
|
Single slope solar distiller
|
V-corrugated basin and PCM
|
3.76
|
37.1
|
12.0
|
Kabeel et al., (2021b)
|
Tubular solar still
|
V-corrugated basin and wicks
|
4.15
|
51.4
|
44.82
|
Elshamy and El-Said, (2018)
|
Tubular solar still
|
Semicircular corrugated absorber
|
3.40
|
34.1
|
26.47
|
Kabeel et al., (2019b)
|
Pyramid solar distiller
|
TiO2 nano mixed with black paint
|
6.60
|
-
|
6.10
|
Abdullah et al., (2020a)
|
Single slope solar distiller
|
- Flat steel trays at the basin sides
- Flat trays with internal mirrors
- Flat trays with internal and
bottom exteral mirrors
- Flat trays with internal and
(bottom+top) exteral mirrors
|
2.95 3.40 4.05
4.20
|
41.0 42.0 44.0
50.0
|
45.0 57.0 84.0
95.0
|
This
study
|
Hemispherical
solar distiller
|
- Basi with flat iron trays
- Basi with corrugated iron trays
- Basi with flat iron trays and wicks
- Basi with corrugated iron trays
and wicks
|
4.40
5.50
5.95
7.05
|
38.72 48.2852.16 61.67
|
14.30
42.85
54.55
83.12
|
Economic analysis
In this section, an economic analysis is conducted to assess the economic feasibility of the developed modifications applied for the proposed hemispherical distiller to determine and compare the cost per unit of distilled water produced of all studied distillers. The daily freshwater productivity for HSD-VIT&WM, HSD-FIT&WM, HSD-VIT, HSD-FIT, and CHSD were 7.05, 5.95, 5.50, 4.40, and 3.85 kg/m2.d respectively. The cost analysis is accomplished accounting on Eqs. (2-8) that were described by (Attia et al., 2021e; Kabeel and Abdelgaied, 2017);
The cost per freshwater liter (CW) can be calculated as follows:
$${C}_{W}= \frac{TAC}{{M}_{W,annual}}= \frac{TAC}{{M}_{W,daily*N}}$$
2
Where TAC is the sum of total annual cost, Mdaily is the daily accumulative yield, and N refers to the number of operating days of still over the year, which is assumed to be 270 days to attain reliable water cost results and consider the scarcity of solar energy through the seasons of the year (Kabeel and Abdelgaied, 2019). TAC can be computed as follows;
Where AFC is the yearly fixed cost that is described by Eq. (4), whereas AMOC is the annual maintenance and operating cost which is computed by Eq. (6) (Kabeel and Abdelgaied, 2019); While ASV depicts the yearly salvage value which is represented by Eq. (7);
Where TCC is the total capital cost of the distiller system and CRF is the capital recovery factor that is represented by Eq. (5);
$$CRF=\frac{{K}_{d} {\left(1+{K}_{d}\right)}^{i}}{{\left(1+{K}_{d}\right)}^{i}-1}$$
5
Where Kd is the yearly discount rate (12%), and i refers to the lifetime of the still (10 years).
The salvage value of the distiller (S) is considered 20% of the total capital cost (Kabeel and Abdelgaied, 2019). While the sinking funding index (SFF) can be represented as:
$$SFF= \frac{{K}_{d}}{{\left({K}_{d}=1\right)}^{i}-1}$$
8
Table 3 demonstrates the findings of the cost analysis of the proposed hemispherical distillers. The economical findings revealed that the cost per litre of freshwater for the HSD-VIT&WM, HSD-FIT&WM, HSD-VIT, and HSD-FIT were lower than CHSD by 41.72% (0.0081 $/L), 33.81% (0.0092 $/L), 25.18% (0.0104 $/L), and 10.79% (0.0124 $/L), respectively.
Table 3
Economic assessment for the proposed hemispherical distillers.
Financial Parameter | CHSD | HSD-FIT | HSD-VIT | HSD-FIT&WM | HSD-VIT&WM |
---|
Total capital cost of the still, TCC ($) | 66.16 | 67.63 | 70.55 | 67.63 | 70.55 |
Annual fixed cost, AFC ($) | 11.71 | 11.97 | 12.486 | 11.97 | 12.486 |
Annual maintenance and operating cost, AMOC, ($) | 3.513 | 3.591 | 3.746 | 3.591 | 3.746 |
Salvage annual value, ASV ($) | 0.754 | 0.771 | 0.804 | 0.771 | 0.804 |
Total annual cost, TAC ($) | 14.47 | 14.79 | 15.43 | 14.79 | 15.43 |
Distillate productivity per year, (L/m2.year) | 1039.5 | 1188 | 1485 | 1606.5 | 1903.5 |
Cost per litre of freshwater productivity, Cw ($/L) | 0.0139 | 0.0124 | 0.0104 | 0.0092 | 0.0081 |