According to the primary text books of physics, pure water boils to produce steam at 100°C when the pressure equals 1 atmosphere or 760 mm of mercury, provided the heat supplied equals 640 Kcal for every Kilogram of water. That means, to produce steam, you need to boil water, so it changes its phase from liquid to gas. However, scientists are proving that it is possible to produce steam from water without boiling it – simply by supplying the latent heat necessary to change the phase.
Boiling is not necessary for producing steam if the vessel containing water is lined with a black material capable of absorbing a range of visible and infrared wavelengths of light. This material can create heat from sunlight and pass it on to the water, creating steam without the water going through the boiling stage.
According to a report in the Science Advances, scientists have created such a new, extremely black material. The material is a deep black color as it reflects very little visible light. The base material is pocked with tiny channels or Nano pores, over which there is a layer of gold nanoparticles each only a few billionths of a meter wide. This arrangement can absorb light from the visible spectrum and from some parts of the infrared spectrum, reaching 99% efficiency.
As the structure of the material is highly porous, it floats on water surface and soaks up the sunrays falling on it. As light falls on a gold nanoparticle within one of the Nano pores, photons in the applicable range of wavelength stir up electrons on the gold surface. The electrons oscillate back and forth, and the oscillating electrons are known as plasmons. The plasmons produce intense localized heating, vaporizing the water nearby.
To excite a plasmon, the wavelength of light has to match the size of the nanoparticle it hits. Therefore, to use as much of the sun’s spectrum as possible, scientists have created gold nanoparticles in the pores of a variety of sizes. That allows the material to absorb a large range of the wavelengths of light.
Jia Zhu, material scientist at the Nanjing University of China, is pioneering the research group. According to Jia, scientists have been successful in producing steam with plasmonic material earlier as well. However, the new material is different as it improves the efficiency of the entire process, and converts more than 90% of the light energy falling on it to steam.
According to mechanical engineer Nicholas Fang of MIT, not a part of the research, the team has actually produced an intriguing solution. Although scientists have achieved higher efficiencies with other material such as carbon nanotubes, the new material, though not as efficient, will be cheaper to manufacture.
Steam is a very useful form of energy and generating steam efficiently can help many industries. These include producing freshwater from saline water, also known as desalination, running steam engines and sterilization. In the industry, steam is used also for humidification, moisturization, cleaning, atomization, motive, propulsion, drive, and heating. There are several steam-using equipment as well.
