As a possible solution to increase the availability of clean, potable water, Indian Institute of Science (IISc) researchers have developed a novel thermal desalination system which can work using solar energy.
The most common methods for desalination are membrane-based reverse osmosis and thermal desalination. However, both consume a lot of energy.
According to IISc, thermal desalination systems work by heating saltwater and then condensing the resulting vapour to obtain freshwater.
Environment-friendly
“But the energy required for evaporation is usually obtained from either electricity or combustion of fossil fuels. An environmental-friendly alternative is using solar stills in which solar energy is employed to evaporate saltwater in large reservoirs and the vapour that condenses on a transparent roof is collected. However, during condensation, a thin layer of water forms on the roof, reducing the amount of solar energy that can penetrate the reservoir and therefore, the system’s efficiency,” said IISc.
“As an alternative to such solar stills, the IISc team has developed a novel design for a solar-powered desalination unit that is more energy-efficient, cost-effective and portable, making it convenient to set up in areas with limited access to continuous electricity,” said Susmita Dash, Assistant Professor in the Department of Mechanical Engineering and corresponding author of the study which has been published in Desalination.
The setup, designed by Dash and her PhD student Nabajit Deka, comprises a reservoir of saline water, an evaporator, and a condenser enclosed within an insulating chamber to avoid heat losses to the ambient air. Their system works by using solar thermal energy to evaporate a small volume of water imbibed or “wicked” into the evaporator, which has a textured surface. The wicking of liquid into the evaporator takes advantage of the capillary effect of microscale textures.
“This effect allows liquids to be drawn into narrow spaces of a porous material, much like water being absorbed by a sponge. Utilising this approach, instead of heating the entire liquid volume in the reservoir, results in a significant improvement in the system’s energy efficiency,” says Dash.
Works for groundwater too
Apart from seawater, the system can also work with groundwater containing dissolved salts as well as brackish water. It can be adjusted to align with the shifting positions of the sun during the day.
IISc said that the researchers are currently working on scaling up the system and improving its durability, and increasing the volume of drinking water produced, so that it can be deployed for domestic and commercial use.
