Steam produced using nano-particles

Naomi Halas, Professor of Chemistry at Rice University, Texas, and her team recently spent three days in Seattle demonstrating their exciting new research.

“Luckily,” she said, “it was sunny.” The sun’s appearance was extremely welcome since Halas’ revolutionary research involves using nanoparticles and  sunlight to create steam without reaching the normal boiling temperature of 100°C.

This “solar steam” process is so effective that it can even produce steam from icy cold water. It has an overall energy efficiency of about 24 per cent, but Halas hopes this can be increased when the process is further refined. This is compared to the 15 percent efficiency of photovoltaic cells which, until now, were the most common way of converting sunlight directly into electricity.

Obviously, this process has huge potential for electricity generation, but the Rice team think the first uses will be for sanitation and water generation in developing countries.

Nanoparticles are comparatively cheap to make and, because they essentially act as catalysts, they aren’t used up in the process, allowing them to be reused. And, as we saw in the 18th century, if you can commercially generate steam, you can cause an industrial revolution.  Halas’ project has been funded by The Bill & Melinda Gates foundation in the hope that this is the case.

The process uses nanoparticle beads that are approximately one tenth of the diameter of a human hair. Since they have a diameter which is shorter than the wavelength of visible light, they absorb the light’s energy rather than scattering it as larger particles would.

In Halas’ new apparatus, steam forms in a vessel of water long before the water becomes warm to the touch. This is achieved because the nanoparticle heats up incredibly quickly and transfers that heat to the thin surface of water surrounding it. This water turns into steam, creating an insulating barrier around the nanoparticle so it is unable to heat any more water. The bubble then rises to the surface and the steam is released enabling the nanoparticle to sink again, repeating the process.

The way in which this process allows the energy to be concentrated on small amounts of water rather than heating the whole volume equally is what makes it so revolutionary.

The process will also allow the more complete distillation of solutions: 99 per cent alcohol solutions can now be collected compared to the previous maximum of 95 per cent.

The research was only released last week and, is a while off being commercially viable. So maybe it isn’t time to throw out your kettle just yet, but Halas’ apparatus could cause a revolution in the way steam is produced. “We’re not changing any of the laws of thermodynamics,” Halas said. “We’re just boiling water in a radically different way.”

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