Rainbow Schlieren Deflectometry를 이용한 과냉수 내 비등 기포 계면에서의 응축열전달 측정

Measurement of condensation heat transfer at the interface of boiling bubble in subcooled water using Rainbow Schlieren Deflectometry

The objective of this study is to experimentally measure condensation heat transfer at the vapor-liquid interface of boiling bubbles generated in subcooled water. Rainbow Schlieren Deflectometry (RSD) is an optical technique that allows for the non-intrusive visualization of the temperature gradient field in liquid. It is known that the refractive index of a liquid changes as a function of temperature. When light passes through a liquid medium, the degree of deflection is proportional to the spatial gradient of the temperature field. The deflected light passes through a rainbow filter with a continuous variation in color from the center to the outer boundary. As a result, the temperature gradient field in the liquid can be visualized as a color contour. Boiling experiments in a pool of subcooled water were conducted to visualize the temperature gradient field near the vapor-liquid interface of a vapor bubble. A set of RSD images was obtained for the entire life cycle of a boiling bubble, from nucleation through growth to departure from the heating wall. The temperature gradient field near the vapor-liquid interface around the bubble was carefully analyzed. The condensation heat transfer coefficient was calculated and compared to existing prediction models.