Contactless thermal mapping of high-temperature solar receivers via narrow-band near-infrared thermography

Abstract

We present the design, construction, and successful proof-of-principle demonstration of a thermal camera capable of seeing through glass and other radiatively participating media, and apply the device to map the temperature distribution of a steam-filled windowed solar cavity receiver operating at temperatures up to 1400 °C. This “glass piercing” thermal camera utilizes a narrow bandpass filter with a center wavelength of 772 nm to effectively see through glass and similar optical glazing materials, as well as infrared-active radiatively participating media, to allow direct contactless measurement of the inner surfaces of windowed cavity receivers. By utilizing a standard optical CMOS sensor, the device achieves much higher resolution at a lower cost than traditional thermal cameras operating in the mid-infrared. Using a calibrated photometry sphere, we experimentally determined the device sensitivity (grayscale value per spectral radiance value), which allows the spectral radiance and ultimately temperature to be determined from a simple grayscale image. The calibrated device was then applied to both a blackbody source operating at above 1000 °C, and a high-temperature solar cavity receiver operating above 1400 °C. The results serve as an experimental proof-of-concept for glass-piercing and radiatively-participating-gas-piercing thermography.