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International Heat Transfer Conference 15

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

Measurement of Liquid Film Thickness Formed between Colliding Twin Bubbles during Coalescence Process

Takayuki Morokuma
Yokohama National University, 79-5 Tokiwadai, Hodogaya, Yokohama, 240-8501, Japan

Yoshio Utaka
Yokohama National University, Department of Mechanical Engineering, Tokyo Institute of Technology 2-12-1 0-okayama, Meguro-ku Tokyo 152 JAPAN; School of Mechanical Engineering, Tianjin University, 135 Ya Guan Rd. Tianjin Haihe Education Park, Jinnan District, Tianjin300350, China; Key Laboratory of Efficient Utilization of Low and Medium Grade Energy (Tianjin University), Ministry of Education, China

DOI: 10.1615/IHTC15.flm.008899
pages 3331-3345

SCHLÜSSELWÖRTER: Microscopic measurement, Boiling and evaporation, Bubble coalescence, Liquid film thickness


The objective of this study is to investigate experimentally the formation characteristics, temporal change in thickness distribution, and rupture phenomena of the liquid film that forms between twin approaching bubbles by liquid thickness measurement. There are few studies of the characteristics of a thin liquid film shaped between bubbles when the bubbles coalesce, although liquid film rupture is an important issue for bubble coalescence phenomena. The coalescence of horizontally contacting twin bubbles is experimentally investigated using an isothermal system. The bubbles are generated at the outlets of two horizontally oriented pipes on opposite faces. The thickness of the liquid film that formed between the contacting bubbles in water and ethanol is measured using an improved laser extinction method. The variation in the liquid film thickness at the rupture location and the distribution of the liquid film thickness are measured. The air flow rate and measurement position (transmitted laser position) are adopted as experimental parameters. The bubble approach velocity and the duration from the start of the collision until coalescence are measured by analyzing high-speed images. The liquid film is thinnest just before coalescence near the center of the film when bubble coalescence occurs rapidly. The thinnest part of the film just before coalescence was approximately 0.8 ?m. The thinnest position moves toward the periphery from the center with increasing contact duration and approach velocity, and a ring-shaped thinner area in the liquid film is formed. The minimum thickness just before rupture in the ringshaped area is approximately 0.3 ?m.

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