Thanks for this I have been working with some people at the ICT mumbai on a parabolic trough collector. We succeeded in concentrating solar power at a very modest cost using mirror strips layered in a parabolic shape. The earlier method was to use parabolic mirrors. The problem that remains unsolved is how to capture this heat into a pipe filled with thermic fluid. A number of highly qualified scientists discussed it for years and finally ran out of steam, so to speak. I know of of the original chaps very well. Unusual for a scientist, very practical and has a bias for action. Lets see what he thinks of it. He's probably read the paper already but I'm interested in seeing if there's anything I can contribute
Thanks and regards Narendra Shenoy On Fri, 4 Mar 2022 at 04:41, Thaths via Silklist < [email protected]> wrote: > Keeping this decade-and-a-half-plus thread going.... > > https://news.mit.edu/2022/solar-desalination-system-inexpensive-0214 > > Solar-powered system offers a route to inexpensive desalination > Passive solar evaporation system could be used to clean wastewater, > provide potable water, or sterilize medical tools in off-grid areas. > David L. Chandler | MIT News Office > Publication Date: > February 14, 2022 > PRESS INQUIRIES > <https://news.mit.edu/2022/solar-desalination-system-inexpensive-0214#press-inquiries> > [image: desalination diagram] > Caption: > MIT researchers have developed a solar-powered desalination system that is > more efficient and less expensive than previous methods. In this schematic, > a confined water layer above the floating thermal insulation enables the > simultaneous thermal localization and salt rejection. > Credits: > Image: Courtesy of the researchers > [image: outdoor experimental setups] > Caption: > Researchers test two identical outdoor experimental setups placed next to > each other. > Credits: > Image: Courtesy of the researchers > [image: image shows water layer under one sun solar illumination] > Caption: > The left photograph shows the confined water layer structure. On the > right, an infrared image shows the confined water layer under one sun solar > illumination. Thermal energy is localized in the confined water layer. > Credits: > Image: Courtesy of the researchers > > Previous image Next image > > An estimated two-thirds of humanity is affected by shortages of water, and > many such areas in the developing world also face a lack of dependable > electricity. Widespread research efforts have thus focused on ways to > desalinate seawater or brackish water using just solar heat. Many such > efforts have run into problems with fouling of equipment caused by salt > buildup, however, which often adds complexity and expense. > > Now, a team of researchers at MIT and in China has come up with a solution > to the problem of salt accumulation — and in the process developed a > desalination system that is both more efficient and less expensive than > previous solar desalination methods. The process could also be used to > treat contaminated wastewater or to generate steam for sterilizing medical > instruments, all without requiring any power source other than sunlight > itself. > > The findings are described today in the journal *Nature Communications*, > in a paper by MIT graduate student Lenan Zhang, postdoc Xiangyu Li, > professor of mechanical engineering Evelyn Wang, and four others. > > “There have been a lot of demonstrations of really high-performing, > salt-rejecting, solar-based evaporation designs of various devices,” Wang > says. “The challenge has been the salt fouling issue, that people haven’t > really addressed. So, we see these very attractive performance numbers, but > they’re often limited because of longevity. Over time, things will foul.” > > Many attempts at solar desalination systems rely on some kind of wick to > draw the saline water through the device, but these wicks are vulnerable to > salt accumulation and relatively difficult to clean. The team focused on > developing a wick-free system instead. The result is a layered system, with > dark material at the top to absorb the sun’s heat, then a thin layer of > water above a perforated layer of material, sitting atop a deep reservoir > of the salty water such as a tank or a pond. After careful calculations and > experiments, the researchers determined the optimal size for the holes > drilled through the perforated material, which in their tests was made of > polyurethane. At 2.5 millimeters across, these holes can be easily made > using commonly available waterjets. > > The holes are large enough to allow for a natural convective circulation > between the warmer upper layer of water and the colder reservoir below. > That circulation naturally draws the salt from the thin layer above down > into the much larger body of water below, where it becomes well-diluted and > no longer a problem. “It allows us to achieve high performance and yet also > prevent this salt accumulation,” says Wang, who is the Ford Professor of > Engineering and head of the Department of Mechanical Engineering. > > Li says that the advantages of this system are “both the high performance > and the reliable operation, especially under extreme conditions, where we > can actually work with near-saturation saline water. And that means it’s > also very useful for wastewater treatment.” > > He adds that much work on such solar-powered desalination has focused on > novel materials. “But in our case, we use really low-cost, almost household > materials.” The key was analyzing and understanding the convective flow > that drives this entirely passive system, he says. “People say you always > need new materials, expensive ones, or complicated structures or wicking > structures to do that. And this is, I believe, the first one that does this > without wicking structures.” > > This new approach “provides a promising and efficient path for > desalination of high salinity solutions, and could be a game changer in > solar water desalination,” says Hadi Ghasemi, a professor of chemical and > biomolecular engineering at the University of Houston, who was not > associated with this work. “Further work is required for assessment of this > concept in large settings and in long runs,” he adds. > > Just as hot air rises and cold air falls, Zhang explains, natural > convection drives the desalination process in this device. In the confined > water layer near the top, “the evaporation happens at the very top > interface. Because of the salt, the density of water at the very top > 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 at the top drives the salty liquid to go down.” The water > evaporated from the top of the system can then be collected on a condensing > surface, providing pure fresh water. > > The rejection of salt to the water below could also cause heat to be lost > in the process, so preventing that required careful engineering, including > making the perforated layer out of highly insulating material to keep the > heat concentrated above. The solar heating at the top is accomplished > through a simple layer of black paint. > [image: salt diagram]This gif shows fluid flow visualized by food dye. > The left-side shows the slow transport of colored de-ionized water from the > top to the bottom bulk water. The right-side shows the fast transport of > colored saline water from the top to the bottom bulk water driven by the > natural convection effect. > > So far, the team has proven the concept using small benchtop devices, so > the next step will be starting to scale up to devices that could have > practical applications. Based on their calculations, a system with just 1 > square meter (about a square yard) of collecting area should be sufficient > to provide a family’s daily needs for drinking water, they say. Zhang says > they calculated that the necessary materials for a 1-square-meter device > would cost only about $4. > > Their test apparatus operated for a week with no signs of any salt > accumulation, Li says. And the device is remarkably stable. “Even if we > apply some extreme perturbation, like waves on the seawater or the lake,” > where such a device could be installed as a floating platform, “it can > return to its original equilibrium position very fast,” he says. > > The necessary work to translate this lab-scale proof of concept into > workable commercial devices, and to improve the overall water production > rate, should be possible within a few years, Zhang says. The first > applications are likely to be providing safe water in remote off-grid > locations, or for disaster relief after hurricanes, earthquakes, or other > disruptions of normal water supplies. > > Zhang adds that “if we can concentrate the sunlight a little bit, we could > use this passive device to generate high-temperature steam to do medical > sterilization” for off-grid rural areas. > > “I think a real opportunity is the developing world,” Wang says. “I think > that is where there's most probable impact near-term, because of the > simplicity of the design.” But, she adds, “if we really want to get it out > there, we also need to work with the end users, to really be able to adopt > the way we design it so that they’re willing to use it.” > > “This is a new strategy toward solving the salt accumulation problem in > solar evaporation,” says Peng Wang, a professor at King Abdullah University > of Science and Technology in Saudi Arabia, who was not associated with this > research. “This elegant design will inspire new innovations in the design > of advanced solar evaporators. The strategy is very promising due to its > high energy efficiency, operation durability, and low cost, which > contributes to low-cost and passive water desalination to produce fresh > water from various source water with high salinity, e.g., seawater, brine, > or brackish groundwater.” > > The team also included 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 used facilities supported > by the National Science Foundation. > > > On Tue, May 15, 2018 at 11:25 PM Udhay Shankar N <[email protected]> wrote: > >> On Tue, May 8, 2018 at 7:07 AM gabin kattukaran <[email protected]> >> wrote: >> >> > On Sun, 25 Mar 2018 at 11:57, Udhay Shankar N <[email protected]> wrote: >> > >> > > And some more: >> > >> > >> > >> https://www.wired.co.uk/article/charlie-paton-seawater-greenhouse-desalination-abu-dhabi-oman-australia-somaliland >> > >> > >> > It doesn't stop there - >> http://science.sciencemag.org/content/360/6388/518 >> >> >> NYT has (dis)covered the above research. >> >> https://www.nytimes.com/2018/05/08/science/alan-turing-desalination.html >> >> Udhay >> > > > -- > Homer: Hey, what does this job pay? > Carl: Nuthin'. > Homer: D'oh! > Carl: Unless you're crooked. > Homer: Woo-hoo! > _______________________________________________ > Silklist mailing list > Manage your membership here: > https://lists.digeratus.in/postorius/lists/silklist.lists.digeratus.in/
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