Performance enhancement of a tubular solar still by using stepped basins: An experimental approach

An experimental investigation was conducted on a novel design of a stepped basin tubular solar still (SBTSS) and a tubular solar still (TSS) under different water depths/equivalent water depths in the weather conditions of Egypt. The proposed SBTSS design utilized stepped basins inside the TSS, which allowed for reducing the water depth for the same amount of salt water and volume of air, along with the benefits of a double slope solar still inside the SBTSS. Based on the experimental results, the thermal and exergy efficiencies were obtained for both TSS and SBTSS. The results showed that the novel SBTSS design had higher hourly and accumulated productivity, as well as thermal and exergy efficiencies, compared to TSS at different water depths. The maximum daily productivity recorded was 3826 mL/m2/day and 2572 mL/m2/day for SBTSS and TSS, respectively, at a depth/ equivalent water depth of 1 cm. Moreover, the results indicated that the enhancement in accumulated productivity for SBTSS was 42.28% and 38.85% compared to TSS at water depths of 1.5 cm and 2 cm, respectively. The thermal efficiency for SBTSS and TSS was found to be 36.71% and 24.59%, respectively, at a water depth/ equivalent water depth of 1 cm/10L, with an increment of 49.29% for SBTSS. Additionally, the cost per liter (CPL) of potable water and payback period for SBTSS were about 0.0159 US$/L and 124 days, respectively, at an equivalent water depth of 1 cm with a 10-year still life considered. On the other hand, the CPL of potable water and payback period for TSS at the same water depth were about 0.0185 US$/L and 146 days, respectively.