Engineers at Rice have devised an ingenious process that allows the generation of steam without boiling water using nanotechnology (particles that are extraordinarily small) plus ordinary sunlight. Among other applications, this could revolutionize the possibilities of solar energy.
In the Rice experiment, the researchers stirred a small amount of nanoparticles into water and put the mixture into a glass vessel. They then focused sunlight on the mixture with a lens.
The nanoparticles — either carbon or gold-coated silicon dioxide beads — have a diameter shorter than the wavelength of visible light. That allows them to absorb most of a wave of light’s energy. If they had been larger, the particles would have scattered much of the light.
In the focused light, a nanoparticle rapidly becomes hot enough to vaporize the layer of water around it. It then becomes enveloped in a bubble of steam. That, in turn, insulates it from the mass of water that, an instant before the steam formed, was bathing and cooling it.
Insulated in that fashion, the particle heats up further and forms more steam. It eventually becomes buoyant enough to rise. As it floats toward the surface, it hits and merges with other bubbles.
At the surface, the nanoparticles-in-bubbles release their steam into the air. They then sink back toward the bottom of the vessel. When they encounter the focused light, the process begins again. All of this occurs within seconds.In all, about 80 percent of the light energy a nanoparticle absorbs goes into making steam, and only 20 percent is “lost” in heating the water. This is far different from creating steam in a tea kettle. There, all the water must reach boiling temperature before an appreciable number of water molecules fly into the air as steam.
The phenomenon is such that it is possible to put the vessel containing the water-and-nanoparticle soup into an ice bath, focus light on it and make steam. . . .
Halas said the nanoparticles are not expensive to make and, because they act essentially as catalysts, are not used up. A nanoparticle steam generator could be used over and over. And, as James Watt and other 18th-century inventors showed, if you can generate steam easily, you can create an industrial revolution.