Researchers from the Massachusetts Institute of Technology (MIT) and Shanghai Jiao Tong University in China have developed a low-cost passive photo voltaic evaporation system that may be used to clean wastewater or desalinate saline water to produce potable water.
Most modern attempts at photovoltaic desalination make use of a wick to draw salty water through the device. However, these wicks are susceptible to salt buildup, which reduces the system’s effectiveness and necessitates frequent and ongoing maintenance, making it significantly more expensive and inefficient.
The new research findings were published in the journal Nature Communications by MIT graduate student Lenan Zhang, postdoctoral associate Xiangyu Li, mechanical engineering professor Evelyn Wang, and four others.
The team devised a wick-free technique to avoid the problem of salt accumulation. Their technique consists of a layered structure with dark materials on top to absorb the sun’s heat, followed by a thin layer of water that sits above a perforated layer of cloth, which lies above a reservoir of salty or non-potable water, such as a tank or pond.
“To attain great performance, wicking structures and innovative materials have been used recently.” However, because of the captured pressure, mass flow is restricted. Freshwater is the only thing that evaporates. There is a lot of salt in this constricted porous structure as a result of this. This causes the system to become inefficient due to the accumulation of salt. This poses a problem with trustworthiness. “We avoid employing such materials by following natural convention,” Xiangyu Li told indianexpress.com.
The use of a wick-free technique eliminates the problem of salt accumulation.
After extensive testing, the researchers determined that the best hole diameter for perforated materials (which in the trials was polyurethane) was 2.5 mm all around. The holes were created with a high-pressure waterjet during the experiment, but Li doesn’t rule out the possibility of using other methods in the future.
The small holes promote the exchange of salt between the water on top, and the reservoir below as the water above the layer becomes saltier due to evaporation. The difference in density between the water with collected salt on top and the water below causes this.
“When you look at a road on a hot day, you see some wave-like things in the difference. This happens because hot air near the surface is hotter, causing a faster flow, which causes the refraction with which you perceive those waves.’ Our technology operates on a similar principle, relying on the varying densities of water in the two layers,” Li explained.
“Unlike previous designs with dependability difficulties, we rely on natural convention and the device’s geometry.” It was entirely made out of household items that we purchased on Amazon. According to my calculations, a one-square-meter device will cost around $4,” Li added.
Of course, this system just handles one aspect of the process: evaporation. It should also require a separate condenser to become a fully functional system. However, Li believes that a condenser system may be built to be just as cost-effective as an evaporator.
In ideal conditions, a one-square-meter system like the one described by Li should be able to produce roughly 6.5 liters of water.
The system isn’t without limitations, although: the necessity for a reservoir like a tank or a pond signifies that it will likely be onerous to deploy in really arid areas. Instead, it aims to decentralize desalination and purification for households and communities who stay in distant locations; the place’s geography and different components make it troublesome to enter desalinated water from a centralized plant.
Also, the system is probably going years away from a stage the place it may be mass-produced or deployed because the researchers are nonetheless engaged in enhancing its operational effectivity and understanding what modifications must be made based mostly on numerous environmental and supply components like reservoir water high quality, temperature, and many others.
Published by: Khushboo Mehta
Edited By: Kritika kashyap
