26 September 2022
New metamaterial points to opportunities for efficient power plant inspections
Steam-like material shows that near-infrared imaging could help cameras see through steam droplets surrounding turbines
ROCHESTER - Although imaging of turbines while a power plant is operating would reduce the need to shut down equipment during inspections and lower risk of costly component failures, the dense condensing steam surrounding these turbines prevents inspectors from getting a clear view. In new work, researchers developed a semisolid metamaterial with light scattering properties that closely match those of the steam found in turbines. They used it to show that infrared wavelengths might be helpful for imaging in this challenging environment.
“We had just finished a research project on a different approach for monitoring the structural health of large steam turbine blades when I proposed using high-speed infrared imaging, based in part on prior research at the Electric Power Research Institute (EPRI) that included light transmission measurements through turbine steam at different wavelengths,” explained Marek Kowarz, president, MicroAdventure Technologies LLC. “During the infrared imaging project, done in collaboration with EPRI, it became apparent to us that it would be very useful to simulate light scattering in the turbine environment for development of inspection technologies.”
Marek Kowarz from MicroAdventure Technologies LLC will detail the new research at the Frontiers in Optics + Laser Science Conference (FiO LS) meeting being held in Rochester, New York and online 17 – 20 October 2022. Kowarz’s presentation is scheduled for Monday, 17 October at 17:30 EDT (UTC – 04:00).
Mimicking the unique steam in turbines
To ensure power plants are operating safely, inspectors must routinely check their large turbine blades for wear and cracking. Doing this while the plant is operating is difficult because the large rotating turbines spin very fast and are surrounded by a dense cloud of water nanodroplets that obscures the blades. These unique nanodroplets are inside a vacuum environment and measure 100 to 300 nm, which is 10 to 100 times smaller than the water droplets found in fog.
Because of their small size, the scattering of these nanodroplets is strongly dependent on the wavelength of light used for imaging. Thus far, it has been difficult to study this challenging imaging scenario because it is difficult to reproduce these nanodroplets in a laboratory.
In the new work, the researchers experimented with different types of materials and found that metamaterials based on alumina nanoparticles best replicated the nanodroplets produced by spinning turbines in power plants. Metamaterials use small, carefully designed structures to manipulate light in ways that naturally occurring materials do not. After showing that the fabricated samples exhibited a very uniform steam-like appearance, the researchers imaged test targets through the simulated steam using a monochrome industrial camera and illumination from LED arrays.
A path to efficient inspections
The experiment showed that images acquired using 850 nm near-infrared illumination were much clearer and showed excellent visibility compared to those imaged at 455 nm. Since high-power LEDs and sensitive CMOS detectors are already available for near infrared wavelengths, near-infrared imaging could be promising for imaging through steam during power plant operation.
Kowarz added, “In a follow-on project for EPRI, we developed a prototype imaging probe and demonstrated that it could produce images of small crack-like features moving at Mach 1.5, similar to speeds encountered in power plants. For actual power plant use, the imaging probe would need to be smaller and able to withstand the harsh turbine environment.”
About FiO LS
Frontiers in Optics + Laser Science will be presented in a hybrid conference format comprised of in-person and virtual participation options. The meeting unites Optica (formerly OSA) and American Physical Society (APS) communities for quality, cutting-edge presentations, fascinating invited speakers and a variety of special events. The exhibit features leading optics and photonics companies and technology products. More information at https://www.frontiersinoptics.com.