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Research Papers: Multiphase Flows

Numerical Simulation of Turbulent Mist Flows With Liquid Film Formation in Curved Pipes Using an Eulerian–Eulerian Method

[+] Author and Article Information
Pusheng Zhang

Department of Mechanical Engineering,
Michigan State University,
East Lansing, MI 48824
e-mail: zhangpus@egr.msu.edu

Randy M. Roberts

Chevron Energy Technology Company,
Houston, TX 77002

André Bénard

Department of Mechanical Engineering,
Michigan State University,
East Lansing, MI 48824

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the Journal of Fluids Engineering. Manuscript received November 26, 2012; final manuscript received April 14, 2013; published online June 6, 2013. Assoc. Editor: Francine Battaglia.

J. Fluids Eng 135(9), 091303 (Jun 06, 2013) (10 pages) Paper No: FE-12-1594; doi: 10.1115/1.4024264 History: Received November 26, 2012; Revised April 14, 2013

Turbulent flows of air/water mixtures through curved pipes are modeled in this work using a Eulerian–Eulerian method. This is motivated by the possibility of using computational fluid dynamics (CFD) as a design tool applied to curved pipes feeding a gas/liquid separator. The question is to identify the curvature of such pipes that can promote film formation upstream of the separator and, thus, precondition the flow without creating a large pressure drop. The performance of the mixture theory with a drift flux model and the “realizable” k-ε closure was evaluated in the simulations. The enhanced wall treatment (EWT) was utilized to resolve the flow in the near-wall region. A qualitative study was first conducted to investigate the flow patterns and the liquid film formation in a 180 deg bend. The numerical results were validated by comparing the computed pressure drop with empirical correlations from the literature. Subsequently, the importance of droplet size and liquid volume fraction was investigated by studying their effect on the flow patterns of the continuous phase, as well as their impact on the secondary flow intensity, the pressure drop, and the liquid film formation on the wall. Various pipe geometries were studied to achieve a low pressure drop while maintaining a high droplet deposition. Results show that a combination of the drift flux model with the realizable k-ε closure and EWT for the near-wall treatment appears capable of capturing the complex secondary flow patterns such as those associated with film inversion. The pressure drop computed for various flows appear to be in good agreement with an empirical correlation. Finally, bends with a curvature ratio around 7 appear to be the optimal for providing a small pressure drop as well as a high droplet deposition efficiency in a U-bend.

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References

Figures

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Fig. 1

Schematic of the 3D geometric parameters of a bend with an arbitrary bend angle θ

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Fig. 6

The comparison between the numerical results and Paliwoda's empirical correlation shows a good agreement

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Fig. 4

Water film forms at the inner bend wall called “film inversion,” which is caused by the combined effects of gravity and the secondary flow patterns

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Fig. 3

The air and water streamlines show the development of the flow patterns and the interaction between two phases. The contour of αp shows the liquid film formation along the 180 deg bend.

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Fig. 2

O-type structured mesh used for a cross section. It allows refining the mesh easily close to the wall and prevents a singularity at the center of the pipe.

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Fig. 5

Volume fraction distribution of the water phase shows the location of liquid film at the pipe wall of the outlet cross section

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Fig. 7

Comparison between the single-phase air flow (b) and the air-water flows (c–f) on the secondary flow patterns and the flow intensity at the cross section of 90 deg deflection (a) changing with different droplet size

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Fig. 8

Volume fraction distribution shows the liquid film location at the cross section of 90 deg deflection of a 180 deg bend for different droplet sizes

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Fig. 9

Secondary flow patterns and flow intensity at the cross section of 90 deg deflection for different volume fraction αp

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Fig. 10

Pressure drop through the bend section as a function of (a) the Stokes number, and (b) volume fraction of the water phase

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Fig. 11

Droplet deposition efficiency changing with (a) the Stokes number, (b) volume fraction of the water phase. Efficiencies of 1.0 are not reached since the gas/liquid interface is blurry (set at αp ≥ 0.8), i.e., a small portion of the liquid is not included as part of the film.

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Fig. 12

Plots of the pressure drop and droplet deposition efficiency are shown above as a function of the bend curvature ratio in (a) a horizontal 90 deg bend and (b) a 180 deg bend

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