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Effect of absorber plate surface shape and glass cover inclination angle on the performance of a passive solar still


Hamid Reza Goshayeshi, Mohammad Reza Safaei*

Source title: 
International Journal of Numerical Methods for Heat & Fluid Flow, 2019 (ISI)
Academic year of acceptance: 


Solar-driven water desalination technologies are rapidly developing with various links to other renewable sources. However, the efficiency of such systems severely depends on the design parameters. This paper presents results from an investigation on the effect of the glass cover inclination angle on the performance of two stepped solar still geometries (flat and convex) and the amount of produced distilled water.

Design Methodology Approach

Studied inclination angles of 25°, 27.5°, 30°, 32.5° and 35° were chosen, while other design parameters were fixed.


The investigation showed that the unit with the convex absorber plate had higher average water daily production rate, compared to the output of the flat absorber plate unit. The results also depicted that the inclination angle of the still has a noticeable effect on the performance of solar stills. The value of the critical angle is 32.5°, and the higher inclination angle results in less heat transfer coefficient. This value can be used for design purposes and erases the typical assumption to use lower angles to optimize the productivity of the still.

Practical Implications

Finally, obtained data were used to correlate the Nusselt number for the flat and convex surfaces with different inclination angles of the glass cover.

Originality Value

The outcome of this investigation may find applications to develop highly efficient solar stills to secure more drinkable water in warm, dry lands.