March 5, 2024

Solar-Powered System From MIT Offers a Route to Inexpensive Desalination

The findings are explained in the journal Nature Communications, in a paper that was published on February 14, 2022, by MIT college student Lenan Zhang, postdoc Xiangyu Li, teacher of mechanical engineering Evelyn Wang, and 4 others.
” There have been a lot of demonstrations of truly high-performing, salt-rejecting, solar-based evaporation designs of various devices,” Wang says. “The difficulty has been the salt fouling problem, that people havent truly dealt with. We see these very attractive efficiency numbers, but theyre typically restricted because of durability. Over time, things will foul.”
Researchers test 2 similar outdoor experimental setups positioned beside each other. Credit: Courtesy of the researchers
Numerous attempts at solar desalination systems rely on some kind of wick to draw the saline water through the device, however these wicks are susceptible to salt accumulation and fairly hard to tidy. The result is a layered system, with dark product at the top to soak up the suns heat, then a thin layer of water above a perforated layer of product, sitting atop a deep reservoir of the salty water such as a tank or a pond.
The holes are big enough to enable a natural convective blood circulation in between the warmer upper layer of water and the chillier tank below. That circulation naturally draws the salt from the thin layer above down into the much larger body of water listed below, where it ends up being well-diluted and no longer a problem. “It allows us to accomplish high performance and yet likewise prevent this salt accumulation,” says Wang, who is the Ford Professor of Engineering and head of the Department of Mechanical Engineering.
The left photograph reveals the restricted water layer structure. On the right, an infrared image shows the restricted water layer under one sun solar illumination. Thermal energy is localized in the restricted water layer. Credit: Courtesy of the researchers
Li states that the advantages of this system are “both the trusted operation and the high performance, particularly under extreme conditions, where we can in fact deal with near-saturation saline water. Which indicates its likewise extremely useful for wastewater treatment.”
He includes that much work on such solar-powered desalination has concentrated on novel materials. “But in our case, we use actually affordable, almost household products.” The key was analyzing and understanding the convective circulation that drives this totally passive system, he says. “People state you constantly need brand-new materials, pricey ones, or wicking structures or complex structures to do that. And this is, I believe, the very first one that does this without wicking structures.”
This new technique “offers a promising and efficient course for desalination of high salinity services, and could be a video game changer in solar water desalination,” says Hadi Ghasemi, a teacher of chemical and biomolecular engineering at the University of Houston, who was not related to this work. “Further work is required for evaluation of this principle in large settings and in long runs,” he includes.
Just as hot air increases and cold air falls, Zhang describes, natural convection drives the desalination procedure in this device. In the confined water layer near the top, “the evaporation takes place at the very top user interface. Because of the salt, the density of water at the very leading user interface is higher, and the bottom water has lower density. So, this is an original driving force for this natural convection because the higher density on top drives the salty liquid to decrease.” The water evaporated from the top of the system can then be collected on a condensing surface area, offering pure fresh water.
The rejection of salt to the water listed below could also cause heat to be lost in the procedure, so avoiding that required cautious engineering, consisting of making the perforated layer out of extremely insulating product to keep the heat focused above. The solar heating at the top is achieved through an easy layer of black paint.
Far, the group has shown the concept using small benchtop gadgets, so the next step will be beginning to scale up to gadgets that might have useful applications. Based on their estimations, a system with simply 1 square meter (about a square lawn) of gathering location needs to suffice to provide a familys daily requirements for drinking water, they state. Zhang states they computed that the necessary products for a 1-square-meter device would cost just about $4.
Their test device operated for a week without any signs of any salt accumulation, Li says. And the gadget is extremely stable. “Even if we apply some extreme perturbation, like waves on the seawater or the lake,” where such a gadget could be set up as a floating platform, “it can return to its initial equilibrium position very quick,” he states.
The required work to equate this lab-scale proof of concept into practical industrial gadgets, and to improve the total water production rate, need to be possible within a couple of years, Zhang states. The very first applications are likely to be providing safe water in remote off-grid areas, or for disaster relief after typhoons, earthquakes, or other interruptions of typical water supplies.
Zhang adds that “if we can concentrate the sunshine a bit, we could utilize this passive device to produce high-temperature steam to do medical sterilization” for off-grid rural locations.
” I believe a real chance is the developing world,” Wang says. “I believe that is where theres most likely impact near-term, because of the simpleness of the design.” However, she adds, “if we truly wish to get it out there, we likewise require to work with completion users, to actually have the ability to adopt the way we develop it so that theyre ready to use it.”
” This is a new technique toward fixing the salt accumulation problem in solar evaporation,” states Peng Wang, a teacher at King Abdullah University of Science and Technology in Saudi Arabia, who was not associated with this research. “This sophisticated design will influence brand-new developments in the style of advanced solar evaporators. The technique is really promising due to its high energy effectiveness, operation durability, and low cost, which adds to low-priced and passive water desalination to produce fresh water from various source water with high salinity, e.g., seawater, brine, or brackish groundwater.”
Reference: “Highly efficient and salt declining solar evaporation through a wick-free restricted water layer” by Lenan Zhang, Xiangyu Li, Yang Zhong, Arny Leroy, Zhenyuan Xu, Lin Zhao and Evelyn N. Wang, 14 February 2022, Nature Communications.DOI: 10.1038/ s41467-022-28457-8.
The group likewise consisted of Yang Zhong, Arny Leroy, and Lin Zhao at MIT, and Zhenyuan Xu at Shanghai Jiao Tong University in China. The work was supported by the Singapore-MIT Alliance for Research and Technology, the U.S.-Egypt Science and Technology Joint Fund, and utilized centers supported by the National Science Foundation.

By David L. Chandler, Massachusetts Institute of Innovation
February 17, 2022

MIT scientists have developed a solar-powered desalination system that is more efficient and cheaper than previous approaches. In this schematic, a confined water layer above the floating thermal insulation makes it possible for the simultaneous thermal localization and salt rejection. Credit: Courtesy of the researchers
Passive solar evaporation system might be utilized to tidy wastewater, offer drinkable water, or sanitize medical tools in off-grid locations.
An approximated two-thirds of humanity is impacted by scarcities of water, and numerous such locations in the developing world also deal with an absence of trustworthy electricity. Extensive research study efforts have actually thus concentrated on ways to desalinate seawater or brackish water utilizing just solar heat. Many such efforts have actually run into issues with fouling of devices brought on by salt accumulation, however, which often includes complexity and expense.
Now, a group of scientists at MIT and in China has actually come up with a service to the issue of salt build-up– and at the same time established a desalination system that is both more efficient and more economical than previous solar desalination methods. The process might also be utilized to deal with infected wastewater or to generate steam for disinfecting medical instruments, all without requiring any source of power aside from sunshine itself.

The outcome is a layered system, with dark material at the top to soak up the suns heat, then a thin layer of water above a perforated layer of product, sitting atop a deep tank of the salty water such as a tank or a pond. Because of the salt, the density of water at the really leading user interface is higher, and the bottom water has lower density. The water vaporized from the top of the system can then be collected on a condensing surface area, providing pure fresh water.
Based on their computations, a system with simply 1 square meter (about a square yard) of collecting area ought to be adequate to offer a familys everyday needs for drinking water, they say. The strategy is very promising due to its high energy performance, operation durability, and low cost, which contributes to passive and low-cost water desalination to produce fresh water from numerous source water with high salinity, e.g., seawater, brine, or brackish groundwater.”