High-speed visualization and image processing of sub-atmospheric water boiling on a transparent heater

The paper is devoted to the processing and analysis of the high-speed visualization data on water pool boiling in the pressure range of 5.5–103 kPa. The study of the vapor bubbles dynamics and evolution of void fraction near a heated wall during boiling was performed using a special design of a transparent heating element and high-speed visualization from its bottom side. To analyze the wide array of video data, automatic image processing programs were developed. As a result, a detailed statistical analysis of the growth curves and departure diameters of vapor bubbles during boiling at different pressures was carried out. It was shown that at ultra-low pressure 5.5 kPa after the departure of massive vapor bubbles the pulsating boiling regime was occurred. A method based on the estimation of void fraction near a heated wall was proposed and implemented for the description of this cyclic boiling regime at low sub-atmospheric pressure.