Sponge coated in bubble wrap boils water by focusing sun’s heat

MIT-Sun-Steam-2
Source: George Ni

Original press release was issued by MIT, written by Jennifer Chu

Usually when we order some fragile items, they come in a somewhat amusing packaging that might employ some in popping craziness. The talk is about the bubble wrap. But some people take it further than others and decide to incorporate it into science. Engineers from MIT probably thought along those lines and came up with a pretty handy bubble-wrapped, sponge-like device that soaks up natural sunlight and heats water to boiling temperatures, generating steam through its pores.

“I kept asking myself, ‘Can we basically boil water on a rooftop, in normal conditions, without optically concentrating the sunlight? That was the basic premise.” says Gang Chen, the Carl Richard Soderberg Professor in Power Engineering and the head of the Department of Mechanical Engineering and one of the leaders of the research.

Building on their solar-absorbing structure they developed in 2014this design named “solar vapor generator” is cost-effective as it requires no expensive mirrors or lenses to concentrate the sunlight, but instead relies on a combination of relatively low-tech materials to capture ambient sunlight and concentrate it as heat. The heat is then directed toward the pores of the sponge, which draw water up and release it as steam.

According to Tao Deng, professor of material sciences and engineering at Shanghai Jiao Tong University, this new device offers a totally new approach for solar steam generation. Its key advantage is that it eliminates the need of the expensive optical concentrator, which significantly determines the cost of solar steam generator system. Consisting of only a sponge, bubble wrap to suppress the heat loss and a thin sheet of copper, the whole design may offer inexpensive alternatives for various applications. The group believes it could be used to desalinate small bodies of water, as a residential water heating, medical tool sterilization or to treat wastewater.

In one of their experiments, the researchers managed to use the sponge-like device to heat water to its boiling temperature of 100 degrees Celsius, even on relatively cool, overcast days. The sponge also converted 20 percent of the incoming sunlight to steam.

“The cost is pretty competitive [compared to the other solar-based technologies that rely on optical concentration],” says George Ni, an MIT graduate student, one of the lead authors of the research. “It’s kind of a different approach, where before, people were doing high-tech and long-term [solar absorbers]. We’re doing low-tech and short-term.”

“Clever use of both the bubble wrap and commercially available selective absorber not only improve the solar harvesting efficiency but also lower the system cost.“ says Tao Deng. Ni further adds that the currently used solar-based technologies are designed to last 10 to 20 years and require expensive parts and maintenance. This low-cost design could operate for one to two years before needing to be replaced.

Michal Madaras

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