Instant Steam by Solar Heating of Nanoparticles in Water
by Daroio Borghin 20 Nov 2012
Solar illumination of broadly absorbing metal or carbon nanoparticles dispersed in a liquid produces vapor without the requirement of heating the fluid volume. When particles are dispersed in water at ambient temperature, energy is directed primarily to vaporization of water into steam, with a much smaller fraction resulting in heating of the fluid. Sunlight-illuminated particles can also drive H2O–ethanol distillation, yielding fractions significantly richer in ethanol content than simple thermal distillation. These phenomena can also enable important compact solar applications such as sterilization of waste and surgical instruments in resource-poor locations.
A team of researchers at Rice University has developed a new technology that uses light-absorbing nanoparticles to convert solar energy directly into steam. Even though it is already significantly more efficient than solar panels at producing electricity, the technology will likely find its first applications in low-cost sanitation, water purification and human waste treatment for the developing world.
Because of its very small footprint and high efficiency, this new development promises to make steam economically viable on a much smaller scale. Sterilizing medical waste and surgical instruments, preparing food and purifying water could soon become within reach of a large chunk of the developing world, that doesn't have access to the electrical grid.
The Rice technology relies on light-absorbing nanoparticles. When they are submerged and then illuminated, these particles can very quickly reach temperatures well above the boiling point of water. At this stage, they quickly dissipate heat through their very small surface area, which almost instantly results in 150°C (300°F) steam generated right at the surface of the particle. The system is so effective that it can even turn icy-cold water directly into vapor with ease.
The technology converts about 80 percent of the energy coming from the sun into steam. With the current iteration, passing the resulting steam to a turbine would generate electricity with an overall efficiency of 24 percent (compared to a solar panel's typical efficiency of around 15 percent). As the technology is further refined, the researchers say there is still room for improvement on the efficiency front.
Other potential uses could be powering hybrid air-conditioning and heating systems that run off of sunlight during the day and off of electricity at night. The system has also proved very promising in distilling water, with an experiment finding that the technology is about two and a half times more efficient than existing commercially available systems.
The project was awarded a grant from the Bill and Melinda Gates Foundation to create a small-scale system for treating human waste in areas lacking sewer systems or electricity. In the meantime, Rice engineering undergraduates have already created a solar steam-powered autoclave that can sterilize medical and dental instruments in clinics lacking electricity.