Bubble and liquid turbulence characteristics of bubbly flow in a large diameter vertical pipe

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International Journal of Multiphase Flow 34 (2008) 767–785 www.elsevier.com/locate/ijmulflow

Bubble and liquid turbulence characteristics of bubbly flow in a large diameter vertical pipe
M.E. Shawkat a, C.Y. Ching b,*, M. Shoukri b
a

Fuel and Fuel Channel Safety Analysis, Nuclear Safety Solutions Ltd., 700 University Avenue, Toronto, Ontario,Canada M5G 1X6 b Department of Mechanical Engineering, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4L7 Received 3 August 2007; received in revised form 11 January 2008

Abstract The bubble and liquid turbulence characteristics of air–water bubbly flow in a 200 mm diameter vertical pipe was experimentally investigated. The bubble characteristics were measured using adual optical probe, while the liquid-phase turbulence was measured using hot-film anemometry. Measurements were performed at six liquid superficial velocities in the range of 0.2–0.68 m/s and gas superficial velocity from 0.005 to 0.18 m/s, corresponding to an area average void fraction from 1.2% to 15.4%. At low void fraction flow, the radial void fraction distribution showed a wall peak which changedto a core peak profile as the void fraction was increased. The liquid average velocity and the turbulence intensities were less uniform in the core region of the pipe as the void fraction profile changed from a wall to a core peak. In general, there is an increase in the turbulence intensities when the bubbles are introduced into the flow. However, a turbulence suppression was observed close to thewall at high liquid superficial velocities for low void fractions up to about 1.6%. The net radial interfacial force on the bubbles was estimated from the momentum equations using the measured profiles. The radial migration of the bubbles in the core region of the pipe, which determines the shape of the void profile, was related to the balance between the turbulent dispersion and the lift forces. Theratio between these forces was characterized by a dimensionless group that includes the area averaged Eotvos number, slip ratio, and the ratio between the apparent added kinetic energy to the actual kinetic energy of the liquid. A non¨ ¨ dimensional map based on this dimensionless group and the force ratio is proposed to distinguish the conditions under which a wall or core peak void profile occursin bubbly flows. Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Two phase; Bubbly flow; Large diameter; Pipe; Turbulence; Interfacial force; Bubble migration

1. Introduction The local distribution of the bubble and the liquid turbulence characteristics such as the void fraction, bubble diameter, bubble velocity, liquid average and turbulent velocities in two-phase bubbly flow is important tounderstand the interaction between the phases. It is now well established that the scale of the pipe can have an effect on the flow patterns and phase distribution. Typically, for a vertical upward bubbly flow, when the diameter of
Corresponding author. Tel.: +1 905 545 9140x24998; fax: +1 905 572 7944. E-mail address: chingcy@mcmaster.ca (C.Y. Ching). 0301-9322/$ - see front matter Ó 2008 ElsevierLtd. All rights reserved. doi:10.1016/j.ijmultiphaseflow.2008.01.007
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the pipe (Dpipe) is greater than about 100 mm, the bubbles tend to migrate toward the pipe centerline forming a ‘‘corepeak” void fraction distribution instead of a ‘‘wall-peak” void profile that is commonly observed in smaller diameter pipes (Cheng et al., 1998; Yoneda et al., 2002; Shen et al., 2005). Herringe and Davis(1976), however, indicated that the void fraction profile was also dependant on the size of the bubbles, and obtained a core-peak void profile in a 50.8 mm diameter pipe by introducing larger bubbles to the flow. This was later corroborated by Nakoryakov et al. (1996) in a 14.8 mm pipe, where the void profile changed from a wall to a core peak when the gas injector was changed to obtain larger bubble...