Experimental examination of a natural vacuum desalination system integrated with evacuated tube collectors

Abstract

A solar natural vacuum desalination system was experimentally investigated. Using a barometric water column and creating an equilibrium with atmospheric pressure and gravity, vacuum conditions were maintained inside the evaporation chamber throughout the day, which led to the beginning of evaporation at lower temperatures and as a result, lower energy consumption compared to conventional methods. Solar evacuated tubes were used to more efficiently absorb solar radiation and raise the temperature of saline water. In addition, at the system startup, a vacuum pump was utilized to fill the water column and create vacuum conditions. Then, the existing vacuum in the system was maintained naturally through the barometric column. The effect of creating a vacuum with four different operating pressures on freshwater production was studied. Results indicated the better performance of the system at decreased system pressure. The highest hourly and daily productions were 1.134 kg/m2 hr and 8.065 kg/m2 day, respectively. In addition, the switching-off-period of the vacuum pump was studied. The increase of this period from one day to three days led to increasing the overall system efficiency from 47.6% to 50%. Moreover, the cost of produced freshwater was obtained as 0.094 $/L.