Experimental study of effects of different heat sources on the performance of the hybrid multiple-effect diffusion solar still

Abstract

This study proposes a hybrid multiple-effect diffusion solar still (HMED) operating with various heat sources, such as solar thermal energy, electric heater and waste heat. The performance characteristics of the HMED may differ with the type of evaporation heat source used even with the same amount of thermal energy supplied (Qin). The effects of the different type of heat sources on the production of distillate and thermal efficiency (performance ratio, PR) of the HMED are experimentally analysed in the Republic of Korea (latitude 36.40°N and longitude 127.36°E). The experimental results show that the HMED can be operated with not only solar energy but also with waste heat or combination of them. The PR of the HMED is the lowest for solar heat (0.18 – 0.71) and the highest for waste heat (2.32), even though Qin from waste heat is lower (6 – 9 MJ) than global solar radiation (11 – 23 MJ/m2). The effect of the thermal insulation of both glass sidewalls on the productivity is larger for solar energy (16.7% enhancement) than for waste heat (5.3% enhancement). A lower initial depth of the seawater in the basin increases the productivity, but an optimum depth exists. The optimum feed flow rate of seawater to the multiple-effect diffusion section (MED) increases with Qin, but its optimum ratio to the amount of evaporation in each effect-plate of the MED may be within a range of 4.6 – 2.8, regardless of Qin.