Performance of basin type stepped solar still enhanced with superior design concepts

Abstract

It is difficult maintaining a minimum water depth in a conventional basin type solar still, as the required area is quite large. To overcome this difficulty, the R&D community proposed a stepped solar still in an attempt to increase the production per unit area by decreasing the thermal inertia of the water mass, where the area of the basin is minimized via the utilization of small trays. However, stepped solar still is still potential for further enhancement. It is leaned from the literature, that adding internal and external reflectors, absorber materials (fins) and external condensers are considered superior in enhancing the absorption, evaporation and condensation processes of the basin type solar still. Combining these design concepts concurrently with stepped solar still to enhance its performance is still a missing link in the literature. In this study, a previous work of stepped solar still is selected to apply these modifications on it and propose it as a new design. Energy balance model is developed to compare the performance of the stepped solar still before and after modification. The energy balance results are obtained by solving the energy balance equations for various elements: absorber plate, saline water and glass cover of the solar still. Hourly solar radiation and hourly ambient temperature of clear sky day conditions are used as input data in the energy balance model. The hourly performance of the stepped solar still is compared before and after modification under the following evaluation parameters: temperature difference between saline water and glass cover, evaporation/convective/radiative heat transfer coefficients, solar still productivity and solar still efficiency. The results showed that the hourly values of evaluation parameters after modification are always higher of that before modification. This increment is tested statistically to confirm its significance. So, the differences in the mean values of each evaluation parameter before and after modification are tested by statistical paired t-test. The test results confirmed that there is a significant difference in the mean values of each evaluation parameter before and after modification. Moreover, the daily productivity of the stepped solar still after modification increased from 6.9 to 8.9kg/m2; this represents 29% enhancement compared to before modification. Finally, based on the results of the evaluation parameters and the statistical test, the thermal performance of the proposed stepped solar still is considerably improved through the new modification.