Theoretical analysis of a single-stage and two-stage solar driven flash desalination system based on passive vacuum generation

An innovative solar driven flash desalination system is proposed. The system uses the natural forces of gravity and atmospheric pressure to create a vacuum. Single-stage and two-stage concepts have been outlined. The main components include evaporator(s), condenser(s), collection tanks, heat source and seawater circulation pump. Partial heat recovery is attained by first passing the feedwater through the condenser(s), followed by the heat source. Additional distillate output is obtained in the second stage of the two-stage system without any extra heat addition, since the high temperature brine from the first stage is passed and flashed in the second stage. Theoretical analysis of the single-stage and two-stage concepts is done for the system when coupled with constant temperature heat source and solar collector. When coupled with a solar collector of 1 m² area, a single-stage system produces 5.54 kg of water in 7.83 h, while the two-stage system produces 8.66 kg in 7.7 h. The performance ratios obtained, including the efficiency of solar collectors, are 0.48 and 0.75 for a single-stage and two-stage system respectively, or 0.748 and 1.350 if only the useful heat collected by the solar collector is considered.