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The researchers first tested the structure by running experiments in the lab, using a solar simulator that mimics the characteristics of natural sunlight at varying, controlled intensities. They found that the structure was able to heat a small basin of water to the boiling point and produce superheated steam, at 122 C, under conditions that simulated the sunlight produced on a clear, sunny day. When the researchers increased this solar intensity by 1.7 times, they found the device produced even hotter steam, at 144 C.
On Oct. 21, 2017, they tested the device on the roof of MIT’s Building 1, under ambient conditions. The day was clear and bright, and to increase the sun’s intensity further, the researchers constructed a simple solar concentrator — a curved mirror that helps to collect and redirect more sunlight onto the device, thus raising the incoming solar flux, similar to the way a magnifying glass can be used to concentrate a sun’s beam to heat up a patch of pavement.
With this added shielding, the structure produced steam in excess of 146 C over the course of 3.5 hours. In subsequent experiments, the team was able to produce steam from sea water, without contaminating the surface of the device with salt crystals. In another set of experiments, they were also able to collect and condense the steam in a flask to produce pure, distilled water.
Chen says that, in addition to overcoming the challenges of contamination, the device’s design enables steam to be collected at a single point, in a concentrated stream, whereas previous designs produced more dilute spray.
“This design really solves the fouling problem and the steam collection problem,” Chen says. “Now we’re looking to make this more efficient and improve the system. There are different opportunities, and we’re looking at what are the best options to pursue.”
This research was supported in part by MIT’s Abdul Latif Jameel Water and Food Systems Lab (J-WAFS), and from MIT’s S3TEC Center, an Energy Frontier Research Center funded by the Department of Energy, Office of Science, Basic Energy Sciences, and by an Early Postdoc Mobility Fellowship from the Swiss National Science Foundation.
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