5. Measures to improve the productivity of solar stills

As analyzed above, the elements of the environment are the objective factors and cannot change. In this section we focus on the main measures taken in the design of the still.

#### 5.1. Reducing the cover's temperature

In the experiments on a stepped solar still [22], a cooling water flow is sprayed with 5 l/min for 30 s on the cover with the time between two injections being 10 and 20 min. The schematic diagram of the experimental stepped solar still is shown in Figure 8. Experimental results show that, for a day with average solar radiation of 600 W/m<sup>2</sup> , the distilled water obtained is 4.45 and 4.35 l/m2 corresponding to a period of 10 and 20 min between two injections, compared with 4.08 l/m2 in the case with no cooling water spray to the coverings, which rises to 9 and 6.6%, respectively, as can be seen in Figure 9.

Similarly, in the active (forced circulated) solar still [12], the forced convection also helps to cool the covering surface, increasing the production of distilled water. When the speed of air flow in the distillation system reached 0.005 m/s, the output of distilled water was 3.53 compared to 3.05 l/m<sup>2</sup> in the case of traditional devices, with an increase of 15.7%. This result is consistent with results of Husham [19], as stated in Section 4.2.3.

#### 5.2. Taking advantage of the latent heat of evaporation

In this study, a double-basin solar still (DBSS) combined with evacuated glass tubes has been fabricated and tested to compare it with a single-basin solar still (SBSS) with evacuated glass tubes. Figures 10 and 11, respectively, show the schematic diagrams of these two types of stills. Experimental results are shown in Figure 12. The outputs of distilled water of the two types

are 6.49 and 4.99 l/m2

Figure 10. Single-basin solar still coupled with evacuated glass tubes.

good sunny day (700 W/m2

seen in Figure 13.

, respectively, on a day with 529 W/m<sup>2</sup> of radiation. Thus by utilizing the

), the amount of water collected using this heat exchanger was 6.8

latent heat of evaporation, the yield of the solar double basin still was increased by 30%.

In a study on improvement of the Carocell solar distillation equipment [23], a heat exchanger with a coil size of 760 220 13 (mm) and a total length of pipe Φ8 of 6.5 m was fabricated and mounted just below the distillation equipment to utilize the heat of evaporation. On a

Figure 9. Distillate outputs in the case of no cooling water on the still cover (VS) with cooling water sprayed on the cover.

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compared to 5 l/m2 in the case of the original Carocell still where an increase of 36% can be

In the solar active still [12], taking advantage of latent heat of steam is achieved by circulating air flow through the recovery heat exchanger back to the distillation system. When the speed

Figure 8. The schematic diagram of the experimented stepped solar still [19].

Factors Affecting the Yield of Solar Distillation Systems and Measures to Improve Productivities http://dx.doi.org/10.5772/intechopen.75593 169

Figure 9. Distillate outputs in the case of no cooling water on the still cover (VS) with cooling water sprayed on the cover.

Figure 10. Single-basin solar still coupled with evacuated glass tubes.

5. Measures to improve the productivity of solar stills

show that, for a day with average solar radiation of 600 W/m<sup>2</sup>

is consistent with results of Husham [19], as stated in Section 4.2.3.

to 9 and 6.6%, respectively, as can be seen in Figure 9.

5.2. Taking advantage of the latent heat of evaporation

Figure 8. The schematic diagram of the experimented stepped solar still [19].

5.1. Reducing the cover's temperature

168 Desalination and Water Treatment

As analyzed above, the elements of the environment are the objective factors and cannot

In the experiments on a stepped solar still [22], a cooling water flow is sprayed with 5 l/min for 30 s on the cover with the time between two injections being 10 and 20 min. The schematic diagram of the experimental stepped solar still is shown in Figure 8. Experimental results

4.45 and 4.35 l/m2 corresponding to a period of 10 and 20 min between two injections, compared with 4.08 l/m2 in the case with no cooling water spray to the coverings, which rises

Similarly, in the active (forced circulated) solar still [12], the forced convection also helps to cool the covering surface, increasing the production of distilled water. When the speed of air flow in the distillation system reached 0.005 m/s, the output of distilled water was 3.53 compared to 3.05 l/m<sup>2</sup> in the case of traditional devices, with an increase of 15.7%. This result

In this study, a double-basin solar still (DBSS) combined with evacuated glass tubes has been fabricated and tested to compare it with a single-basin solar still (SBSS) with evacuated glass tubes. Figures 10 and 11, respectively, show the schematic diagrams of these two types of stills. Experimental results are shown in Figure 12. The outputs of distilled water of the two types

, the distilled water obtained is

change. In this section we focus on the main measures taken in the design of the still.

are 6.49 and 4.99 l/m2 , respectively, on a day with 529 W/m<sup>2</sup> of radiation. Thus by utilizing the latent heat of evaporation, the yield of the solar double basin still was increased by 30%.

In a study on improvement of the Carocell solar distillation equipment [23], a heat exchanger with a coil size of 760 220 13 (mm) and a total length of pipe Φ8 of 6.5 m was fabricated and mounted just below the distillation equipment to utilize the heat of evaporation. On a good sunny day (700 W/m2 ), the amount of water collected using this heat exchanger was 6.8 compared to 5 l/m2 in the case of the original Carocell still where an increase of 36% can be seen in Figure 13.

In the solar active still [12], taking advantage of latent heat of steam is achieved by circulating air flow through the recovery heat exchanger back to the distillation system. When the speed

Figure 11. Double-basin solar still coupled with evacuated glass tubes.

• The stepped still maintains the distance between the water and the cover at only 1 cm,

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• Creating good conditions for condensation to flow into the gutters as well as reducing

The experimental results for distilled water output reached 4.9 l/m<sup>2</sup> with average radiation 635 W/m<sup>2</sup> compared to 3.05 l/m<sup>2</sup> in the case of traditional equipment, which rose about 60%, as

thermal condensation resistance of the water condensing on coverings.

Figure 14. Distillate outputs of a stepped solar still versus a conventional solar still.

Figure 13. Distillate outputs of 2 m<sup>2</sup> Carocell solar still, with versus without a heat exchanger.

reducing natural convective obstacles.

shown in Figure 14.

Figure 12. Experimental distillate outputs of the single-basin solar still versus the double-basin solar still.

of air flow in the distillation equipment reached 0.005 m/s, the output of distilled water obtained was 5.94 compared to 3.53 l/m<sup>2</sup> in the case of no circulation, which rose to 68%.

#### 5.3. Reducing the gap between the glass cover and the water level

In order to reduce the gap between the glass and the water level in the still, a stepped solar distillation equipment was designed, fabricated and tested, as shown in Figure 8 [22]. Some advantages of this device:

• Over a full year, the total energy radiation projected onto the tilted surface was larger than the horizontal surface.

Factors Affecting the Yield of Solar Distillation Systems and Measures to Improve Productivities http://dx.doi.org/10.5772/intechopen.75593 171

Figure 13. Distillate outputs of 2 m<sup>2</sup> Carocell solar still, with versus without a heat exchanger.


The experimental results for distilled water output reached 4.9 l/m<sup>2</sup> with average radiation 635 W/m<sup>2</sup> compared to 3.05 l/m<sup>2</sup> in the case of traditional equipment, which rose about 60%, as shown in Figure 14.

Figure 14. Distillate outputs of a stepped solar still versus a conventional solar still.

of air flow in the distillation equipment reached 0.005 m/s, the output of distilled water obtained was 5.94 compared to 3.53 l/m<sup>2</sup> in the case of no circulation, which rose to 68%.

Figure 12. Experimental distillate outputs of the single-basin solar still versus the double-basin solar still.

In order to reduce the gap between the glass and the water level in the still, a stepped solar distillation equipment was designed, fabricated and tested, as shown in Figure 8 [22]. Some

• Over a full year, the total energy radiation projected onto the tilted surface was larger than

5.3. Reducing the gap between the glass cover and the water level

Figure 11. Double-basin solar still coupled with evacuated glass tubes.

170 Desalination and Water Treatment

advantages of this device:

the horizontal surface.

condenser resulted in the distilled water output reaching 6 l/day, almost 15% higher than the output of a still without external condenser, which achieved 5.23 l/day on a day with an

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Theoretical and empirical research was conducted to assess the impact of forced convection on the solar distillation equipment [12]. The schematic diagram of the experiment is shown in Figure 2. A conventional solar still with a collecting area of 2,67m<sup>2</sup> (2,44 m 1095 m), with an inside fan to change the speed of air flow, was made to measure parameters and process experimental data. Results for a typical day is shown in Figure 17 where the water output

The simulation results of SOLSTILL for the production of distilled water for a whole year and the device performance in three cases—(i) forced convection with external condenser and no moist air circulated back to the still, (ii) forced convection with external condenser and moist air circulated back to the still, and (iii) traditional distillation equipment (natural convection) show that the outputs and still efficiencies in the three cases are, respectively, 3.87, 4.76 and

To increase the working temperature of the water in the equipment in order to increase the production of distilled water, the research group used vacuum tubes to heat the water in the basin [21]. Experimental results corresponding to the day with solar radiation of 514 W/m2 for

Figure 17. The effect of forced convection in the device to produce distilled water. (1) Data empirical forced convection. (2) The data forced convection theory. (3) Data empirical natural convection. (4) Data natural convection theory.

.

average radiation intensity of 517.54 W/m<sup>2</sup>

5.5. Creating forced convection in the device

3.10 l/m<sup>2</sup> and 42.9, 53.9 and 34.1% [12].

increased 30–100% compared to a conventional solar still.

5.6. Increasing the working temperature of water in the still

Figure 15. Single-basin solar still coupled with evacuated glass tubes and external condenser.

#### 5.4. Separating the processes of evaporation and condensation in the device

Section 4.4.1 presented the use of an external condenser and a heat recovery to take advantage of moist air stream at high temperature and humidity returning to the still (forced convection).

For a traditional (natural convective) still, the research group manufactured and tested a still with additional external condenser [21]. The schematic diagram of the experiment is shown in Figure 15, and the experimental results of the solar still with external condenser in comparison with the still without the external condenser are shown in Figure 16. The use of the external

Figure 16. Experimental distillate output of single-basin solar still without external condenser versus with external condenser.

condenser resulted in the distilled water output reaching 6 l/day, almost 15% higher than the output of a still without external condenser, which achieved 5.23 l/day on a day with an average radiation intensity of 517.54 W/m<sup>2</sup> .

#### 5.5. Creating forced convection in the device

5.4. Separating the processes of evaporation and condensation in the device

Figure 15. Single-basin solar still coupled with evacuated glass tubes and external condenser.

Section 4.4.1 presented the use of an external condenser and a heat recovery to take advantage of moist air stream at high temperature and humidity returning to the still (forced convection). For a traditional (natural convective) still, the research group manufactured and tested a still with additional external condenser [21]. The schematic diagram of the experiment is shown in Figure 15, and the experimental results of the solar still with external condenser in comparison with the still without the external condenser are shown in Figure 16. The use of the external

Figure 16. Experimental distillate output of single-basin solar still without external condenser versus with external

condenser.

172 Desalination and Water Treatment

Theoretical and empirical research was conducted to assess the impact of forced convection on the solar distillation equipment [12]. The schematic diagram of the experiment is shown in Figure 2. A conventional solar still with a collecting area of 2,67m<sup>2</sup> (2,44 m 1095 m), with an inside fan to change the speed of air flow, was made to measure parameters and process experimental data. Results for a typical day is shown in Figure 17 where the water output increased 30–100% compared to a conventional solar still.

The simulation results of SOLSTILL for the production of distilled water for a whole year and the device performance in three cases—(i) forced convection with external condenser and no moist air circulated back to the still, (ii) forced convection with external condenser and moist air circulated back to the still, and (iii) traditional distillation equipment (natural convection) show that the outputs and still efficiencies in the three cases are, respectively, 3.87, 4.76 and 3.10 l/m<sup>2</sup> and 42.9, 53.9 and 34.1% [12].

#### 5.6. Increasing the working temperature of water in the still

To increase the working temperature of the water in the equipment in order to increase the production of distilled water, the research group used vacuum tubes to heat the water in the basin [21]. Experimental results corresponding to the day with solar radiation of 514 W/m2 for

Figure 17. The effect of forced convection in the device to produce distilled water. (1) Data empirical forced convection. (2) The data forced convection theory. (3) Data empirical natural convection. (4) Data natural convection theory.

the production and performance of the device were, respectively, 5.86 l/m2 and 50.3%, compared with production of 3.10 l/m2 and efficiency of 34.1% of a conventional solar still.

[5] Kabeel AE, El-Agouz SA. Review of researches and developments on solar stills. Desali-

Factors Affecting the Yield of Solar Distillation Systems and Measures to Improve Productivities

http://dx.doi.org/10.5772/intechopen.75593

175

[6] Badran OO. Experimental study of the enhancement parameters on a single slope solar

[7] Kaushal A, Varun. Solar stills: A review. Renewable and Sustainable Energy Reviews.

[8] Muftah AF, Alghoul MA, Fudhodi A, Abdul-Majeed MM, Sopian K. Factors affecting basin type solar still productivity: A detailed review. Renewable and Sustainable Energy

[9] Sharshir SW, Yang N, Peng G, Kabeel AE. Factors affecting solar stills productivity and improving techniques: A detailed review. Applied Thermal Engineering. 2016. 10.1016/j.

[10] Kabeel AA, Omara ZM, Essa FA, Abdullah AS. Solar still with condenser—A detailed

[11] Dunkle RV. Solar water distillation: The roof type still and a multiple effect diffusion still. In: International Developments in Heat Transfer, American Society of Mechanical Engi-

[12] Nguyen BT. SOLSTILL—A simulation program for solar distillation systems. In: Proceed-

[13] Duffie JA, Beckman WA. Solar Engineering of Thermal Processes. 4th ed. New York: John

[14] ASHRAE Systems and Equipment Handbook. New York: American Society of Heating,

[15] AHRI. Forced-Circulation Air-Cooling and Heating Coils. Standard 410. Arlington, Aus-

[16] Cooper PL. Digital simulation of transient processes solar still. Solar Energy. 1969;12:333-346 [17] Khalifa AJN, Hamood AM. Effect of insulation thickness on the productivity of basin type solar stills: An experimental verification under local climate. Energy Conversion and

[18] Garg HP, Mann HS. Effect of climatic, operational and design parameters on the year round performance of single sloped and double sloped solar still under Indian arid zone

[19] Husham MA. Seasonal performance evaluation of external passive solar stills connected to condensers. Journal of Advanced Science and Engineering Research. 2012;2:1-11

[20] Tiwari GN, Singh SK, Bhatnagar VP. Analytical thermal modelling of multi-basin solar

review. Renewable and Sustainable Energy Reviews. 2016;59:839-857

neers, Proceedings of International Heat Transfer; 1961. pp. 895-902

tralia: Air-Conditioning, Heating and Refrigeration Institute; 2014

still. Energy Conversion and Management. 1993;34:1261-1266

ings of EUROSUN; Freiburg; 2004. pp. 96-105

Refrigerating and Air-Conditioning Engineers; 2012

nation. 2011;276:1-12

2010;14:446-453

Reviews. 2014;32:430-447

applthermaleng.2015.11.041

Wiley and Sons Inc.; 2013

Management. 2009;34:2457-2461

conditions. Solar Energy. 1976;18:159-163

still productivity. Desalination. 2007;209:136-143
