Experimental and Numerical Study on Enhancing the Performance of a Stepped Solar Still Using Porous Sponge Materials

Abstract

This study introduces a stepped solar still with porous sponge sheets fixed to the vertical step faces, which enlarges the effective evaporating surface and sustains a thin, capillary-fed film. Three designs were built and tested: a single-slope still, a six-stepped still, and a six-stepped still with 5 mm sponge sheets. The novelty lies in fixing porous sponge sheets to the vertical faces of the steps. Yield of freshwater and instantaneous efficiency were determined in various combinations, that is, base, stepped, and stepped-cum-sponge solar stills. The base solar still produced 298 mL/h at a base temperature of 64.8°C. It achieved an instantaneous efficiency of 42%. The stepped still yielded 431.3 mL/h at 70.6°C and 45%. With the third model stepped-cum-sponge, the yield increased to 469 mL/h, base temperature 71.4°C, and instantaneous efficiency 50%. A CFD model reproduced the temperature trends and supported the higher evaporation strength in the stepped and sponge-lined designs. Overall, the stepped-cum-sponge solar still yielded about 58% more water than the base solar still, without external energy or moving parts.