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Research Papers: Multiphase Flows

Experimental and Numerical Investigation of Single Bubble Dynamics in a Two-Phase Bubbly Medium

[+] Author and Article Information
Arvind Jayaprakash1

 DYNAFLOW INC., www.dynaflow-inc.com, 10621-J Iron Bridge Road, Jessup, Marylandarvind@dynaflow-inc.com

Sowmitra Singh

 DYNAFLOW INC., www.dynaflow-inc.com, 10621-J Iron Bridge Road, Jessup, Marylandsowmitra@dynaflow-inc.com

Georges Chahine

 DYNAFLOW INC., www.dynaflow-inc.com, 10621-J Iron Bridge Road, Jessup, Marylandglchahine@dynaflow-inc.com

1

Corresponding author.

J. Fluids Eng. 133(12), 121305 (Dec 23, 2011) (9 pages) doi:10.1115/1.4005424 History: Received February 11, 2011; Revised October 26, 2011; Published December 23, 2011; Online December 23, 2011

The dynamics of a bubble in a dilute bubbly water-air mixture is investigated experimentally and the results compared with a simple homogeneous compressible fluid model in order to elucidate the requirements from a better advanced numerical solution. The experiments are conducted in view of providing input and validation for an advanced bubbly flow numerical model we are developing. Corrections for classical approaches where in the two-phase flow modeling the dynamics of individual bubble is based on spherical isolated bubble dynamics in the liquid or an equivalent homogeneous medium are sought. The main/primary bubble is produced by an underwater spark discharge from charged capacitors, while the bubbly medium is generated using electrolysis. The size of the main bubble is controlled by the discharge voltage, the capacitors size, and the ambient pressure in the container. The size and concentration of the fine bubbles is controlled by the electrolysis voltage, the length, diameter, arrangement, and type of the wires, and also by the pressure imposed in the container. This enables parametric study of the factors controlling the dynamics of the primary bubble and development of relationships between the primary bubble characteristic quantities such as achieved maximum bubble radius and bubble period and the characteristics of the surrounding two-phase medium: micro bubble sizes and void fraction. The dynamics of the main bubble and of the mixture is observed using high speed video photography. The void fraction of the bubbly mixture in the fluid domain is deduced from image analysis of the high speed movies and obtained as a function of time and space. The interaction between the primary bubble and the bubbly medium is analyzed using both field pressure measurements and high-speed videography. Parameters such as the primary bubble energy and the bubble mixture density (void fraction) are varied, and their effects studied. The experimental data is then compared to a simple compressible fluid medium model which accounts for the change in the medium properties in space and time. This helps illustrate where such simple models are valid and where they need improvements. This information is valuable for the parallel development of an Eulerian-Lagrangian code, which accounts for the dynamics of bubbles in the field and their interaction.

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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Definition sketch of the parameters of the problem of a primary bubble in bubbly medium

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Figure 2

Schematic of a Dynaflow’s spark cell setup

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Figure 3

A picture of the large DYNAFLOW’S Spark-generated bubbles test facility. The Plexiglas tank dimensions are 1 m × 1 m × 1 m and the wall thickness is 2.5 cm.

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Figure 4

Top: An instantaneous snap-shot from the high speed movie. The image window is 0.5 cm × 0.5 cm (100 × 100 pixels). Right: The binary image showing the bubbles in the focal plane.

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Figure 5

Snapshots from a high speed movie of primary bubble growth and collapse in water with no bubble injection. Cell pressure = 17,400 Pa., Electrode depth = 24 cm, Spark Charge = 6000 V.

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Figure 6

Snapshots from a high speed movie of primary bubble growth and collapse in water with bubble injection. Cell pressure = 17,400 Pa., Electrode depth = 24 cm, Spark Charge = 6000 V. 1%.

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Figure 7

Comparison of the evolution of the primary bubble radius versus time for spark-generated bubbles in ‘pure’ water and in a bubbly medium

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Figure 8

Comparison of the evolution of the normalized primary bubble radius versus normalized time for spark-generated bubbles in ‘pure’ water and in a bubbly medium

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Figure 9

Evolution of the primary bubble radius versus time — Comparison of spark-generated bubble results and the analytical model. Experimental data are average of the three experiments.

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Figure 10

Evolution of the primary bubble normalized radius versus normalized time—Comparison of spark-generated bubble results and the analytical model. Experimental data are average of the three experiments.

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Figure 11

Comparison of the void fractions computed from experiments and the analytical/numerical model at 1.71 cm from the electrodes. Also shown are pictures from a high speed movie of the instantaneous bubble size distribution.

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Figure 12

Pressure versus time recorded by a transducer located at a distance of 11 cm from the bubble center

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Figure 13

Pressure versus time computed by the present analytical/numerical model at a distance of 11 cm from the bubble center. Bubble initial conditions are R0  = 0.0033 m and Pg0  = 1,512,942 Pa.

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