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Research Papers: Multiphase Flows

A Separation Criterion With Experimental Validation for Shear-Driven Films in Separated Flows

[+] Author and Article Information
M. A. Friedrich, H. Lan, J. L. Wegener, B. F. Armaly

Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, 400 West 13th Street, Rolla, MO 65409-0050

J. A. Drallmeier1

Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, 400 West 13th Street, Rolla, MO 65409-0050drallmei@mst.edu

1

Corresponding author.

J. Fluids Eng 130(5), 051301 (Apr 25, 2008) (9 pages) doi:10.1115/1.2907405 History: Received July 31, 2007; Revised February 04, 2008; Published April 25, 2008

The behavior of a shear-driven thin liquid film at a sharp expanding corner is of interest in many engineering applications. However, details of the interaction between inertial, surface tension, and gravitational forces at the corner that result in partial or complete separation of the film from the surface are not clear. A criterion is proposed to predict the onset of shear-driven film separation from the surface at an expanding corner. The criterion is validated with experimental measurements of the percent of film mass separated as well as comparisons to other observations from the literature. The results show that the proposed force ratio correlates well to the onset of film separation over a wide range of experimental test conditions. The correlation suggests that the gas phase impacts the separation process only through its effect on the liquid film momentum.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of shear-driven film interaction with separated gas phase flow resulting in partial film separation from the substrate at the corner

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Figure 2

Schematic of test section

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Figure 3

Film width near the test section corner as a function of film flow rate and gas phase velocity

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Figure 4

High speed imaging (2000 frames per second) of the film interaction with the separated gas flow at the test section corner

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Figure 5

Picture of the test section showing the porous surface where the film that remains attached after the corner is removed

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Figure 6

Comparison of the results of the rough wall model developed for this work and the experimental results reported by Wittig (10)

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Figure 7

Typical results from the rough wall model used to predict film characteristics before the corner in the test section

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Figure 8

Momentum analysis for a control volume

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Figure 9

Dimensionless gravitational term from Eq. 16 as a function of Ref

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Figure 10

Film Weber number as a function of Ref

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Figure 11

Dimensionless force ratio as a function of Ref

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Figure 12

Experimentally measured film separation by mass correlated to the calculated force ratio for various gas phase and liquid phase flow conditions; surface tension shown in parentheses

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Figure 13

Predicted effects of the wall angle of the onset of film separation for various gas phase and liquid phase flow conditions

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