Experimental and numerical study of stepped solar still integrated with a passive external condenser and its application

Solar still is used widely to produce clean water from any brackish water. The efficiency of the still depends on the design of the still with respect to the prevailing local ambient conditions. A number of literature discussed about different designs of evaporator on improving the overall efficiency of the still but not on the condenser design. Hence, the present work focuses on the improvement in efficiency by providing a passive external condenser with a stepped design of evaporator. The passive external condenser has shown an increase in the overall efficiency of still by 10.6% in summer and 12.2% in winter. Higher performance was observed in winter than summer when the passive external condenser was added with stepped evaporator (integrated system) and found inverse for the stepped solar still without condenser. Heat transfer analysis was also made to determine the effectiveness of the external condenser in summer and winter. The correlations developed by Dunkle (in: Proceedings of the ASME International Heat Transfer Conference. Part V, International Developmental in Heat Transfer. University of Colorado, Boulder, Colorado, 1961), Hongfei et al. (Energy Convers Manag 43:2469–2478, 2002) and Tsilingiris (Sol Energy 83:420–431, 2009. https://doi.org/10.1016/j.solener.2008.09.007 ) were used to fit the experimental data obtained from the coupled system, and temperature correction factors were introduced along with the correlations to improve the predictions. The application of the external condenser as a heat source was also summarized.