Skin friction measurements in a gas-liquid pipe flow via optical interferometry

Document Type

Article

Publication Date

12-1-1996

Abstract

An instrument for the measurement of wall shear stress in two-phase flows is described. The device, termed a Laser Interferometer Skin Friction (LISF) meter, determines the wall shear by optically measuring the time rate of thinning of a thin oil film placed on the wall of the flow channel. The LISF meter has proven to be a valuable tool for measurement of wall shear in single-phase gaseous flows but, to date, hed not been applied to liquid or gas-liquid flows. This paper describes modifications to the LISF meter developed to facilitate its use in two-phase flows. The instrument's configuration, governing theory, and data reduction procedure are described. Additionally, results of validation experiments for a single-phase water flow are presented which demonstrate the instrument's ability to accurately measure wall shear. Measurements are also presented for two-phase, water-air flows in a duct of square crossection at various superficial gas and liquid velocities within the bubbly flow regime. Results of the measurements reveal that the addition of a very small amount of the gaseous phase increases the wall shear significantly over that in a single-phase water flow. The two-phase wall shear saturates to a maximum and then declines again as the superficial gas velocity is increased. The peak two-phase wall shear is higher at the lower liquid superficial velocity. These trends are qualitatively in agreement with previous measurements obtained in pipes using an electrochemical technique.

Publication Source (Journal or Book title)

American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED

First Page

397

Last Page

403

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