The use of infrared self-emission measurements to retrieve surface temperature of levitating water droplets

Abstract

Levitating small water droplets formed from the upward flow of steam and entrained air above the heated water surface are studied. The case of relatively large droplets in the middle of a droplet cluster which is practically immobile at a small distance from the water surface is considered. The close-up infrared measurements in the spectral absorption band of water are used to identify temperature of the upper surface of the droplet. Both the directional spectral emittance of water surface and the spectral sensitivity of the device are taken into account to formulate an inverse problem for the integral equation. The numerical solution of this problem showed that temperature is minimal at the top of droplet and increases sharply towards the droplet equator. This temperature difference increases almost linearly with the droplet size. The results obtained are expected to be useful for more detailed physical analysis and possible modeling of complex behavior of the levitating droplet clusters.