Productivity augmentation of single-slope solar still using evacuated tubes, heat exchanger, internal reflectors and external condenser

Abstract

ABSTRACT Solar still only finds its application in remote and low population density areas due to its low productivity. This paper aims at improving the freshwater output of single-slope solar still (SS) by coupling it with an evacuated tube collector (ETC). The performance of this ETC coupled still is further enhanced by using a heat exchanger (HE), an internal reflector (IR) and an external condenser. The experiments are carried out with various still modifications, namely, SS (HE+IR+condenser), SS (HE+IR), SS (HE+condenser), and SS (HE only). These modifications are done to expedite the rate of evaporation of basin water and the rate of condensation of the water vapors. The performance of these four arrangements is simultaneously compared with a conventional still on all testing days. Two solar stills of similar dimensions are fabricated to carry out the experiments. One still is applied with modifications while the other is kept conventional. The maximum productivity of 2259 ml and an efficiency of 33.4% is achieved for SS (HE+IR+condenser) as per the experimental results. The results indicated that using a HE and an IR in a solar still had a considerable impact on the still productivity but an external condenser had a little effect on the still performance. The results also indicated that the increase in overall efficiencies of all four modified designs is very small in comparison to conventional still. Abbreviation: ETC: Evacuated tube collector; SS: Solar still; PCM: Phase change material; CS: Conventional still; FPC: Flat plate collector; ASv: Annual salvage value; HTF: Heat transfer fluid; Sv: Salvage value; CPL: Cost per liter; MCannual: Annual maintenance cost; CRF: Capital recovery factor; Pa: Annual freshwater production; SFF: Sinking fund factor; A: First annual cost; TAC: Total annual cost; C: Capital cost; HE: Heat exchanger; t: Bank interest rate; IR: Internal reflector; n: Average life of still.