Abstract
•Different design and operational modifications on stepped still were studied.•Modifications include a condenser, suspended trays, paraffin wax and Al2O3 nanoparticles.•Optimum fan speed was 2000 rpm for stepped still.•The maximum increase in productivity of stepped still was 55% at 2000 rpm.•At 2000 rpm, the thermal efficiency of the stepped still was 76%.
In the present work, we conducted some modifications in the design and operation of stepped distiller to improve its performance. The stepped distiller was modified by installing fixed suspended trays over the vertical walls of the steps to increase the evaporative and exposure surface areas. Also, we created a parallel cavity under the steps’ liner to work as a heat storing space. This cavity was filled by a paraffin wax mixed by Al2O3 nanoparticles as a phase change material (PCM). Besides, the stepped solar distiller performance was studied under integrating the distiller with an external condenser. Furthermore, the performance of the stepped solar still was investigated under different fan speeds of zero, 400, 800, 1200, 1600, 2000, 2400, and 2800 rpm. The performance of the solar still was evaluated under the different conditions individually and combined. Results revealed that the stepped solar distiller, either with or without condenser, had better performance than the reference solar still. At the case of using suspended trays only, the stepped distiller recorded a productivity of 4175 mL/m2 a day versus 3800 mL/m2 a day for the reference distiller with an improvement of 9.8%. Moreover, using the suspended trays and Al2O3/paraffin wax mixture in the parallel cavity increased the productivity of the solar still by around 40%, where the productivity was 5740 and 4100 mL/m2 a day for the stepped and reference stills, respectively. In addition, the optimum fan speed obtaining the maximum productivity improvement for the stepped distiller over the conventional still was 2000 rpm, where the productivity of the stepped still was improved by 55% over that of the reference still. At this fan speed of 2000 rpm, the daily distillate of the conventional and stepped distillers was 4000 and 6200 mL/m², respectively. Finally, the average daily thermal efficiency of the stepped solar still was 46%, 48.7%, and 52.4% when using the suspended trays, suspended trays with PCM, suspended trays with PCM and fan at 2000 rpm, respectively. While the average thermal efficiency of the reference basin distiller was ranged between ~ 38 – 41%. Finally, the cost of the distilled water of stepped still and reference still is 0.014 and 0.015 $/L, respectively.