Autoclave systems widely used to sterilize equipment with saturated steam in developed countries may not be as frequently deployed in rural or resource-limited areas due to the lack or expense of the power and fuel required for their operation. Engineers from MIT and the Indian Institute of Technology turned to a virtually ubiquitous energy resource — the sun — to power autoclaves in these regions.

The passive solar-powered autoclave is assembled with off-the-shelf components for generating solar-heated water and an optically transparent aerogel. The lightweight silica aerogel material provides thermal insulation and reduces the rate of heat loss from the solar autoclave by tenfold. A copper plate with a heat-absorbing A transparent silica-based aerogel provides thermal insulation. Source: Lin Zhao et al.A transparent silica-based aerogel provides thermal insulation. Source: Lin Zhao et coating, bonded to a set of pipes on the underside, forms the core of the sterilization system. Under solar exposure, water flowing through the pipes absorbs heat and generates high-temperature steam with the aid of the transparent insulating hydrogel applied on top and the placement of polished aluminum mirrors on each side of the unit to direct extra sunlight to the plate.

Gravity feeds water from a tank into the plate as steam rises to the top of the enclosure and is fed out through another pipe, which carries the pressurized steam to the autoclave. A steady supply of steam must be maintained for 30 minutes to achieve proper sterilization.

Field tests of a small-scale version of the device in Mumbai, India, confirmed that the system can produce the saturated steam needed for sterilization at 128° C and 250 kPa for the required half hour period. A unit of between 1 and 3 m2 would be sufficient to power a benchtop autoclave of the kind typically used in a doctor’s office and could be constructed for about $160 once the necessary aerogel material is commercialized.

In addition to the sterilization of medical instruments, the solar-powered autoclave technology described in Joule might also be of value in food and beverage processing systems and other industrial processes that rely on high-temperature steam, which is typically provided by fossil-fuel powered boilers.

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