According to the World Health Organization (WHO) and UNICEF, 1.8 billion people worldwide only have access to water contaminated with feces, with no infrastructure to purify it of the toxins that cause cholera, dysentery, typhoid, polio and other too-often fatal diseases. Even worse, UNICEF predicts that extreme weather events resulting from climate change are making access to safe drinking water even more challenging.
To address this global scarcity of fresh water, six mechanical engineering students at Stevens Institute of Technology have focused their Senior Design project on improving the design of a low-cost, solar-powered desalination device to efficiently convert enough seawater to fresh water to meet the daily water consumption requirements for one person.
“We all have a strong interest in sustainability,” said Shawn Coulter ’21, a mechanical engineering major who is concentrating his studies in sustainability. “We were also drawn to helping people who are less fortunate. And our research quickly showed that a lot of the available products are for more developed countries that have access to electricity and a means of running clean water at all times, with the goal of purifying the water further, whereas ours decontaminates water straight from the sea or from a brackish source. And most in-home devices cost around $200, but ours comes out to about $50.”
A fresh approach to fresh water
The team, consisting of Dom Squillaro ‘21, Shawn Coulter ‘21, Ryan Caplis ‘21, Sean Kunz ‘21, Daniel O’Connor ‘21, and Joseph Ranaldi ‘21, modeled its design on a passive solar-powered desalination system, known as a solar still, that was recently co-developed and proven by researchers at MIT and in China. The system uses an insulated array of flat solar evaporators and condensers in which the water is heated, turned into a gas, and then cooled and condensed into a liquid, so the distilled water can be collected separate from the dissolved ions such as salt.
“There aren’t many other diffusion stills, especially multiple-stage diffusion stills,” said Squillaro, another mechanical engineering major. “We wanted to reduce the cost, verify the technology, and optimize the device so it could be commercialized. We're using most of the physical principles that they're using, but we're not using the same design or materials.”
The Stevens team tweaked everything, from the wick structure materials that absorb the water, to the tiers of plates, to the coatings that make the surfaces hydrophobic, thereby improving the efficiency of the delivery of clean water.
The team manufactured the frame of the modular design on the 3D printer in Squillaro’s basement, adding a heat lamp to consistently replicate the sun, borrowing a half-liter plastic food-storage container to serve as the collection basin, tearing off paper towels for wicks, and testing with brackish water from the nearby Hudson River.
Once water is poured into the basin, it wicks up the paper towels into the device, where it evaporates and condenses on a series of copper plates. Solar energy powers the topmost level, and then is recycled along with heat generated from condensation to support optimal efficiency in the device’s lower levels. Team members run the tests up to eight hours at a time.
The trick now is to extract the distilled water droplets.
“We need to figure out a way to get the water down the plate and channeled out of the device to be collected and consumed,” Coulter said. Until then, they’re weighing the device before and after processing the water, and calculating the difference in water weight.
“Theoretical data shows that after five hours of sunlight, we could realize about 100 milliliters of water,” Squillaro said, “and our actual results indicate we could get more than that.”
They’ll also be designing an integrated base and a stand to support the idea of commercialization on an industrial scale for large freshwater production at affordable pricing.
Soaking up the learnings
“With their limited knowledge and experience, these students found the solution and built and tested a viable prototype,” praised their advisor, Chang-Hwan Choi, professor of mechanical engineering in the Schaefer School of Engineering & Science. “And they used the existing foundation from MIT, but they did it from scratch. They are very motivated and committed, and their success in making this device work is very impressive.”
The students are grateful for the support they’ve received from Stevens as well.
“Professor Choi and other professors helped us drive our project and deepen our understanding,” said Kunz ’, who is also a mechanical engineering major with a concentration in sustainability.. “That was key to our goals of raising awareness about people who don't have drinking water, and using this relatively new technology to prove that there are other ways of getting clean drinking water. For a long time, we weren’t getting results. We were going through trial-and-error designing and making the prototype, and meeting with professors to figure out a way that we could prove that condensation was occurring. When we actually saw condensation on the back of the copper plates, that was a really exciting moment for our group. It proved that we knew what we were doing and could get this to work.”
That real-life aspect is critical, offering the engineers a tantalizing glimpse of entrepreneurism.
“It can be difficult for engineering students to pick up business skills,” Coulter said. “It's gratifying to see our work pay off in terms of showing our concepts and our engineering, and then also being able to talk about it and sell people on the idea that we actually have a solid device.”
“We're also interested in getting it to developing countries through other organizations such as the United Nations, the Federal Emergency Management Agency, and WHO,” added Ranaldi, a mechanical engineering major concentrating in sustainable energy. “It’s rewarding that we’ve been able to see all these kinds of devices through articles we’ve read, and then make something that is operational that can help people in crisis, and people in developing countries as well. It makes me feel good that we were able to take the heat from the sun – or our lamp at this point -- and create drinking water. It’s pretty remarkable.” Joseph will be putting his degree to use at Jaros, Baum & Bolles after graduation to design and develop HVAC systems
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