Experimental Performance Evaluation of a Solar Still Coupled with a Vacuum Heat Exchanger

Directly or indirectly, water affects all facets of life. Without it, there would be no vegetation on land, no oxygen for animals to breathe and the planet would look entirely different than it does today. Only 1% of the freshwater is accessible for utilize in the household, agricultural and industrial sectors. Industrial rapid development along with the worldwide population growth around the world have resulted in an increase in the freshwater demand. Among all the renewable energy resources, the solar energy has the highest potential in Iran and therefore, using the solar powered desalination systems can be a solution to provide freshwater in the regions have severe water crisis. The solar desalination systems are energy consuming and therefore using solar stills in the remote locations is more feasible and affordable. In the present study, a solar distillation system integrated with a solar parabolic through and a vacuum type heat exchanger has been designed and evaluated during five sunny days in October, 2015. During the evaluation time period, the environmental parameters of solar radiation, air temperature and wind speed were recorded every 15 minutes. Then, the effect of these environmental parameters on the performance of the solar concentrator and the heat exchanger as well as the daily productivity of the system was investigated. The obtained results showed that solar radiation has the most considerable effect on the performance of the solar concentrator as a function of oil temperature after leaving the concentrator and before entering the heat exchanger. Moreover, it has been investigated that the vacuum pressure of the heat exchanger has a significant effect on the vapor productivity of the system. The maximum distillate productivity of the system was recorded to be 1.5 liter/day with the average solar radiation value of 1227.68 W/m2 under the vacuum pressure of 0.5 bar.