Mechanical engineering students are using the sun to power an autoclave that sterilises medical instruments, helping solve a long-standing health issue for developing countries.
The students at Rice University, Texas used a Capteur Soleil, a device created decades ago by French inventor Jean Boubour to capture the energy of the sun in places where electricity - or fuel of any kind - is hard to get. In attaching an insulated box containing the autoclave, the students transformed the device into a potential lifesaver.
The Capteur Soleil looks something like an ultramodern lawn swing. Its spine is a steel A-frame, and a bed of curved mirrors beneath the frame produces steam by focusing sunlight along a steel tube at the frame's apex. Rather than pump steam directly into the autoclave, the team's big idea was to use the steam to heat a custom-designed conductive hotplate.
"It basically becomes a stovetop, and you can heat anything you need to," says Sam Major, a member of the team which is also made up of Daniel Rist, David Luker and William Dunk. "As long as the autoclave reaches 121 Celsius for 30 minutes (the standard set by the Centres for Disease Control and Prevention), everything should be sterile, and we've found we're able to do that pretty easily.”
According to Major, one person could easily adjust the Capteur Soleil by ratcheting up the back leg to align the mirrors with the sun. Within half an hour of receiving strong sunlight, it will begin to produce steam, which will in turn heat the patterned hotplate and then the standard-issue, FDA-approved autoclave. With good midday sun, Major says it takes 40 minutes to an hour to begin significant heating of the autoclave.
The autoclave, which looks like a tricked-out pressure cooker, has a steamer basket inside.
"We put about an inch of water inside, followed by the basket with the tools and syringes," Major says. "We've used some biological spores from a test kit, steamed them, and then incubated them for 24 hours and they came back negative for biological growth. That means we killed whatever was in there."
Tucked inside a plywood frame, the autoclave is wrapped in silicon-based Thermablok insulation, which has the highest R-value of any known material and is a spinoff from NASA research into thermal protection for the space shuttle. "This thin layer does most of the work," Major says. "We used standard pink insulation around the inside just to make the box stronger."
"This is really the latest iteration of a much larger project," adds Doug Schuler, the team's faculty adviser. "We already have a version of the Capteur Soleil being used in Haiti for cooking, but we felt it could do more."