Wall Shear Stress Induced by Taylor Bubbles in Inclined Flow Channels

J Tihon,V Pěnkavová,J Vejražka,Petra Dančová,Petr Novontý

doi:10.1051/epjconf/20134501089

Abstract

The motion of single air bubbles in flat channels is experimentally investigated. The electrodiffusion technique of near-wall flow diagnostics is applied to measure the wall shear stress distribution under large rising bubbles. The measurements are synchronized with the visual observation of bubble movement by a high-speed camera. The analysis of video records provides information on the bubble shape and terminal velocity. The experiments are carried out for three different channel configuration (with heights of 1.5, 4, and 8 mm), cover a wide range of channel inclination angles (from horizontal to vertical position), and dealing with both the bubbles in stagnant and in co-flowing water. The directionally sensitive, two-strip electrodiffusion probe is proved to be an effective tool to investigate the near-wall flow response to translating bubbles. It provides information not only on the wall shear rate distribution, but also detects the location of near-wall flow reversal, gives an estimate of the thickness of liquid film separating the large bubble from the wall, and provides also the characteristics of capillary waves appearing in the bubble tail region. The effect of channel inclination angle on the modification of wall shear stress distribution along the upper and bottom wall is also discussed.

Highlights

The motion of large bubbles in vertical tubes received considerable attention since the pioneer paper of Dumitrescu [1]
The directionally sensitive, two-strip electrodiffusion probe is proved to be an effective tool to investigate the near-wall flow response to translating bubbles. It provides information on the wall shear rate distribution, and detects the location of near-wall flow reversal, gives an estimate of the thickness of liquid film separating the large bubble from the wall, and provides the characteristics of capillary waves appearing in the bubble tail region
The experiments on Taylor bubbles rising in stagnant or co-flowing liquid provided some new results on the bubble shape, the bubble velocity and the wall shear rate brings along by bubbles in inclined rectangular channels

Summary

Introduction

The motion of large bubbles in vertical tubes received considerable attention since the pioneer paper of Dumitrescu [1]. The comprehensive experimental studies on long bubbles in cylindrical tubes done by White and Beardmore [2], Nicklin et al [3] and Zukolski [4]. In the inertia dominated flow regime (Eo > 40), the terminal rise velocity of large bubbles UB depends on the square root of the product of tube diameter D and gravitational acceleration g. A significant increase in this terminal velocity is observed for the bubble rising in inclined tubes of medium sizes (see e.g. White and Beardmore [2], Zukolski [4], or Bendiksen [5]). The effect of tube inclination on the large bubble velocity is not completely understood, especially the role of surface and viscous forces taking place for small inclinations.

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