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In the present experimental work, the effect of air circulation on increasing heat transfer rates within the duct was studied. Three air circulation speeds are implemented: 2400, 1800, and 1200 rpm. In addition, the effect of the distance between the heat source and the location of the circulating fan on heat transfer rates was investigated using three different distances: 20, 40, and 60 cm. The Exhaust fan, placed at the outlet of the duct, changed its speed to three values: 2850, 2140, and 1425 revolutions per minute. The Reynolds range ranged from 65,000 to 175,000. The results showed that the best thermal performance is achieved when the exhaust fan speed, air circulation speed, and the distance between the heat source are 1425 rpm, 2400 rpm, and 60 cm, respectively.

Existence of potable water is considered as one of the important issues that are related to the survival of human life, especially in fresh water scarce areas. So, it is necessary to find a solution to this problem. In the current work, the productivity of fresh water in conventional single-slope single-basin solar still is increased by using two modification methods. The first method is reflecting the solar ray to the still basin by using aluminum foils that are pasted on the interior surfaces of the still walls. This method will enhance the fallen solar rays on basin water and reduce heat losses. The second method increases the evaporation surface area by introducing blackened stainless steel balls with different diameters at the still basin. Balls of two diameters chosen: 5 and 10 mm. The experimental results show that the productivity of solar still with 10 mm-diameter balls is higher than that of the conventional solar still by 38.07%. The corresponding values of the stills with 5 mm-diameter balls and aluminum foils are 31.41 and 14.87%, respectively. The thermal efficiency of the highest productivity solar still is 27.81%. Other stills are characterized by lower thermal efficiencies by various rates.

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