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First Thermal and Fluids Engineering Summer Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

INVESTIGATION OF BUBBLE FREQUENCY IN SLUG FLOW REGIME FOR FLOW BOILING IN A SINGLE ROUND UNIFORMLY HEATED MICRO-CHANNEL

DOI: 10.1615/TFESC1.mph.012657
pages 1887-1900

Amen Younes
Department of Mechanical and Industrial Engineering, Concordia University, 1455 de Maisonneuve Blvd. W, Montreal, QC, Canada, H3G 1M

Ibrahim Hassan
Department of Mechanical and Industrial Engineering, Concordia University, Montreal, Quebec, Canada, H3G1M8; Mechanical Engineering Department, Texas A&M University at Qatar P O Box 23874, Doha, Qatar

Lyes Kadem
Department of Mechanical and Industrial Engineering, Concordia University, 1455 de Maisonneuve Blvd. W, Montreal, QC, Canada, H3G 1M


KEY WORDS: saturated flow boiling heat transfer, Slug flow regime, flow pattern maps, drift flux model, bubble frequency, micro-channel, uniform heat flux, liquid film, elongated bubble

Abstract

Slug flow is an essential flow pattern observed in micro-channels where its transition boundaries in micro-channels are characterized by two complex hydrodynamic phenomena, the bubble confinement and bubble coalescence. In this paper, an analytical model for predicting the main characteristics of the slug flow including the bubble frequency for flow boiling in horizontal micro-channel is developed for diabatic flow conditions. The influence of surface tension, shear, and inertial forces has been taken into account. The model is developed based on the principal of drift flux model, and a fully developed slug unit is chosen as a control volume for deriving the equations of motion. The effects of main operating conditions, mass and heat fluxes, on bubble length and bubble frequency have been investigated. The critical vapor qualities which represent the boundaries of slug flow regime have been estimated based on the most proper diabatic flow pattern map available in literature for the chosen tested data base. The model has been validated using the available bubble length and frequency database for flow boiling of two working fluids (R134a, and R245fa) in 0.509 mm and 3.0 mm inner diameter horizontal mini/micro-tubes for wide range of mass fluxes (300 ≤ G ≤ 1000 kg/m2. s). This study has shown that the mass flux has a significant effect on bubble frequency. The model predicted the tested data of bubble length and bubble frequency with a good agreement with a mean absolute error (MAE) of 25.18 % and 31.2 % respectively.

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