Numerical Investigation on the Influence of Bubble Velocity, Gravity Level and Bubble Coalescence on Liquid Turbulence Modulation in Horizontal Channel Bubbly Flow

A two phase bubbly flow through a packed bed was studied for dominant bubble breakup and coalescence mechanisms through experiments and CFD modeling. Data on various two-phase parameters, such as local void fraction, bubble velocity, size, number, and shape were obtained from the high speed video images. Results indicated that when a flow regime changed from bubbly to either trickling or pulsing flow, the number of average size bubbles significantly decreased and the shape of majority of bubbles was no longer spherical. The bubble coalescence and breakup mechanisms depend on local conditions such as local velocity of the bubble and pore geometry. The CFD analysis using CFX software package was carried out to study bubble size distributions. In the analysis the models for interactions were examined for each case of bubble breakup flow and bubble coalescence. A comparative study was performed on the resulting bubble size distributions, breakup and coalescence rates estimated by individual models. For change of bubble size distributions along the axial direction medians was used as an comparative parameter and the CFD results on bubble medians were compared against the experimental data. This comparative study showed that the predictions estimated by CFD analyses with the bubble breakup and coalescence models currently available in the literature do not agree with the experimental data.

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Measurements in the Wake of a Ventilated Hydrofoil

Volume 2, Fora: Cavitation and Multiphase Flow; Fluid Measurements and Instrumentation; Microfluidics; Multiphase Flows: Work in Progress ◽

10.1115/fedsm2013-16062 ◽

2013 ◽

Cited By ~ 1

Author(s):

Seung-Jae Lee ◽

Ellison Kawakami ◽

Roger E. A. Arndt

Keyword(s):

Bubble Size ◽

High Speed ◽

Bubbly Flow ◽

Detection Algorithm ◽

Bubble Velocity ◽

University Of Minnesota ◽

Bubble Detection ◽

Global Threshold ◽

Edge Detection Method ◽

The University

The purpose of this study is to develop the necessary algorithms to determine the bubble size distribution and velocity in the wake of a ventilated or cavitating hydrofoil utilizing background illumination. A simplified experiment was carried out to validate the automatic bubble detection algorithm at Saint Anthony Falls Laboratory (SAFL) of the University of Minnesota. The experiment was conducted in the high-speed water tunnel. First, particle shadow velocimetry (PSV) images of a bubbly flow were collected. All parts of the image that are above the global threshold are segmented by an edge detection method based on the Canny algorithm. The utilized algorithm was made to detect partly overlapping bubbles and reconstruct missing parts. After all images have been analyzed, the bubble velocity can be determined by applying a tracking algorithm. This study has shown that the algorithm enables reliable analysis of irregularly shaped bubbles even when bubbles are highly overlapped in the wake of the ventilated hydrofoil. It is expected that this technique can be used to determine the bubble velocity field as well as the bubble size distributions.

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