Experimental investigation of the growth and detachment of boiling bubbles using X-ray imaging technique: Analysis of subcooled pool boiling phenomena in an ethanol/polyalphaolefin nanoemulsion

초록

Boiling heat transfer has been widely studied owing to its advantages in heat transfer performance. Although various efforts have been made to improve heat transfer during the boiling process, the difficulty of observing boiling bubbles using conventional visualization techniques presents a significant challenge to understanding boiling mechanisms. This study investigates the behavior of single boiling bubbles to clarify the heat transfer mechanism during subcooled pool boiling of an ethanol/polyalphaolefin nanoemulsion. The dynamics of individual boiling bubbles were analyzed using a dynamic X-ray imaging technique without optical distortion. A bubble edge detection algorithm was developed to capture bubble shape information from X-ray images, and its performance was verified at different frame rates. Data on individual boiling bubbles were obtained by varying the average heat flux to explain the mechanism of boiling bubble growth. The characteristics of bubble growth and detachment were explained according to the bubble growth stages. The diameter and frequency of bubble departure were analyzed to explain the heat transfer performance. When the average heat flux was 17.9 kW/m2, f x Ddep 3 increased up to 1.15 mm3/s. The results of the present study will contribute to advancing the research domain of improving the boiling heat transfer of nanoemulsions.

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