PERFORMANCE OF A PYRAMID SOLAR STILL USING AIR-COOLED GLASS COVER: AN EXPERIMENTAL STUDY

Document Type : Original Article

Author

Assistant. Prof., Agric. Eng. Dept., Fac. of Agric., Zagazig Univ., Egypt.

Abstract

Cooling the glass cover is considered one of the most effective modifications that affecting the performance of any solar still, particularly at summer season. Many previous studies focused on the water cooling glass cover, but it is important to study another cooling technique to avoid using potable or saline water in this process. Thus, this study aims toinvestigate the possibility of enhancing the performance of a passive square pyramid-shaped solar still in summer season through cooling the glass cover using controlled stream of cooled air. For this purpose, the solar still was coupled to ice-cooling unit provided with a high pressure fan in trial to reduce the temperature of the blowing ambient air over the glass cover. Solar still performance was evaluated using saline water (15000ppm) depth of 4cm without cooling as a control treatment and air-cooled glass cover under different values of air velocities and cooling tactics with taking into consideration the solar still temperatures, productivity and instantaneous efficiency. The obtained results revealed that, the increase of the cooled air velocity from 1.4 m/s (natural wind) to 5 m/s and cooling tactic of 20minon -10min off  gave a remarkable increase in water-inner glass temperature difference (ΔTwgi) from 10 to 21°C  and the productivity from 0.505 to 0.645 L/m2.h at the peak performance hour which led to achieve the highest accumulated  yield of 3.545 L/m2.day and instantaneous efficiency of 43.2% with an increment of about 17 and 10.8%, respectively higher than solar still without cooling. Additionally, the air velocity of 7 m/s has irrelevant effect on the solar still performance, but on the contrary it gave less improvement. Hence, it is obvious that the air-cooled glass cover enhanced the solar still performance.

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References

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Misr Journal of Agricultural Engineering
Volume 35, Issue 1
January 2018
Pages 359-376

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