Local Liquid Velocity Measurements in Horizontal, Annular Two-Phase Flow

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Date
2004Author
Kopplin, Charles R.
Publisher
University of Wisconsin-Madison
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Show full item recordAbstract
Two-phase annular flow is commonly used in both commercial and industrial heat
transfer; however, we do not yet possess a thorough understanding of the nature of the
fluid. Most analytical annular two-phase models are based on a relationship between the
liquid film thickness, liquid film mass flux, and the axial pressure gradient or interfacial
shear stress. The film thickness calculated from these models can then be utilized to
determine the heat transfer coefficient of the flow. Although they are specific to certain
flow regimes and fluids, empirical models remain more accurate than these analytical
models. The key to understanding these flows lies with the liquid film. Therefore, to
better understand the pressure drop and heat transfer of annular two-phase flow, this
study involves the development of local, liquid velocity measurement techniques and
their application to horizontal, wavy-annular two-phase flow.
Two techniques, Bubble Streak Tracking (BST) and Thin Film Particle Image
Velocimetry (TFPIV), have been developed in this study. Utilizing naturally occurring
bubbles within the liquid film, the BST technique determines the liquid velocity by
measuring reflected light streaks from the bubbles. A three-colored LED array creates
directionally unambiguous streaks, while a strobe illuminates interfacial features that
affect the liquid velocity. The TFPIV technique applies a typical micro-PIV system to a
macroscopic flow with the addition of a non-trivial image processing algorithm. This
algorithm successfully overcomes the image noise that occurs when applying PIV to a
two-phase, thin film. Although difficulties arise when processing the BST data, the
results of the BST and TFPIV methods are comparable, making BST an economical
alternative to TFPIV for calculating liquid film velocities.
In this study, these two techniques are applied to horizontal, two-phase flow.
These measurements were made in the wavy, wavy-annular, and annular regimes to
investigate the mechanism responsible for distributing the liquid film around the tube
circumference. The data imply that two of the four major theories are incorrect. While
experiments examining the remaining two mechanisms are inconclusive, images from
both techniques suggest the waves are responsible for distributing the liquid film.
Lastly, the TFPIV method was used to measure time-averaged velocity profiles
within the liquid film of a wavy-annular flow: the first profile measurement of a liquid
film at this scale. While the profile at the bottom of the tube is similar to the universal
velocity profile utilized in annular two-phase models, the profile at the side and top of the
tube exhibit a much different behavior.
Subject
Thesis (M.S.)--University of Wisconsin--Madison, 2004.
Dissertations Academic Mechanical Engineering.
University of Wisconsin--Madison. College of Engineering.
Permanent Link
http://digital.library.wisc.edu/1793/7612Description
Under the supervision of Professor Timothy A. Shedd; 107pp.
Citation
Kopplin, C.R. (2004). Local Liquid Velocity Measurements in Horizontal, Annular Two-Phase Flow. Master's Thesis, University of Wisconsin-Madison.