Published on November 21st, 2012 | by James Ayre0
New Solar Technology Creates Steam Without Boiling Water
A revolutionary new way to create steam simply by using sunlight has been discovered by researchers. The method is able to bring an entire container of fluid to boiling point, even a container of icy cold water.
The new method has many potentially very useful applications. These include the creation of very inexpensive and compact devices that can purify water, the sterilization of medical equipment, sewage treatment, and more energy-efficient alcohol distillation.
“This research opens up a revolutionary new application of nanoparticles in solar energy,” said Paul Weiss, Ph.D., editor-in-chief of ACS Nano, the journal in which the new study was published. “The authors show that sunlight can be used to create steam with virtually no wasteful heating of the surrounding liquid. The potential societal benefits are staggering. They include more energy-efficient distillation of alcohol, a new and highly practical strategy for desalination and water purification and compact solar-driven sources of steam for sterilization and sanitation in resource-poor locations,” said Weiss.
The method is based on the use of metallic nanoparticles that can absorb very large amounts of light, which results in a significant rise in their temperature. That’s a very useful ability, and has generated a lot of interest amongst researchers. Other potential applications include cancer treatment, “laser-induced drug release,” and enhanced bio-imaging.
Previous research on the potential uses of nanoparticles in solar power technologies has focused almost entirely on using them to increase the ability of fluids to conduct heat. There hadn’t been any research done on the abilities of nanoparticles that are mixed into fluids. But as the new research shows, by mixing them directly into a fluid you can create very interesting effects.
“The new report explains that nanoparticles illuminated by light can quickly rise to temperatures above 212 degrees Fahrenheit, the boiling point of water. Steam forms around the surface of each nanoparticle, billons of which can be placed in water or other fluids. Eventually, the vapor escapes from the particle, forming nanobubbles that float to the top of the surface and escape as water vapor or steam, vapors of ethanol in the case of distillation of alcohol for beverages or fuel, or other vapors.”
The report documents, in detail, the varying amounts of steam that are generated in sun-exposed water solutions containing different types of nanoparticles. The two types experimented with were a silicon dioxide/gold type and a carbon type. Both solutions began producing steam in 5-20 seconds after being exposed to sunlight. “The gold nanoparticle solution produced steam in small ‘microexplosive’ bursts. The scientists used the gold nanoparticles to distill alcohol from water and got higher yields of alcohol than would have occurred by boiling the solution.”
The efficiency of the technology is one of its most impressive qualities, over 82 percent of the sunlight that was absorbed by the nanoparticles went directly to generating steam. The overall energy efficiency of the process was 24 percent, and that is without any kind of effort to optimize it.
“These results clearly indicate that solar steam generation is a process that has significant potential for use in a wide variety of energy- and sustainability-relevant applications,” the report states. “Solar-driven, stand-alone waste processing or water purification systems could be developed based on this process. High-temperature (about 240 degrees F. and above) steam produced directly using sunlight could also be used for compact sterilization or sanitation purposes, from the processing of medical waste to the cleaning of medical or dental equipment, minimizing the resource, time and input chemical requirements demanded by current methods. With further development, this approach may be adaptable to higher pressures and other working fluids to drive turbines in solar energy harvesting applications. This approach may also be modified to harvest radiant energy from sources other than the sun, for instance, for the capture of waste energy from geothermal, residential or biological sources.”
The new discovery was just outlined in the American Chemical Society (ACS) journal ACS Nano.
Source: Rice University
Image Credits: Jeff Fitlow/Rice University