Theoretical estimation of the optimum glass cover water film cooling parameters combinations of a stepped solar still

In the present work, theoretical performance evaluation of a stepped solar still using water film cooling over the glass cover is investigated. The effect of film cooling thickness, flow rate, inlet temperature, and air wind speed on the stepped solar still daily productivity is studied. To increase the performance of the stepped solar still outlet water film cooling is recycled as a makeup water. It was found that film cooling thickness, volumetric flow rate, and water film inlet temperature have a significant effect on the daily distillate productivity. The presence of the glass cover water film cooling may increase the stepped still daily productivity by about 8.2% but the value of this percentage mainly depends on the combinations of film cooling parameters. On the other hand, the presence of the film cooling neutralized the effect of air wind speed on the still distillate productivity. Moreover, it was found that the proper combinations of film cooling parameters have a great influence on stepped still productivity and the best combination was: film thickness from 2.5 × 10−4 to 5.5 × 10−4 m, cooling water volumetric flow rate from 4 × 10−5 to 8.5 × 10−5 m3/s, and glass cover length from 2 to 2.8 m. Finally a good agreement between the present theoretical work and previous experimental result has been obtained.