ARTICLE IN PRESS Chemical Engineering Science 61 (2006) 7199 – 7212 www.elsevier.com/locate/ces Flow patterns in the wake of a Taylor bubble rising through vertical columns of stagnant and flowing Newtonian liquids: An experimental study S. Nogueira a , b , M.L. Riethmuller b , J.B.L.M. Campos a , A.M.F.R. Pinto a , ∗ a Centro de Estudos de Fenómenos de Transporte, Departamento de Eng. Química, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200 - 465 Porto, Portugal b von Kárman Institute for Fluid Dynamics, Chaussée de Waterloo, 72B-1640 Rhode Saint Genèse, Belgium Received 31 January 2006; received in revised form 1 August 2006; accepted 3 August 2006 Abstract The flow in the wake and near-wake regions of individual Taylor bubbles rising through stagnant and co-current vertical columns of Newtonian liquids was studied, employing simultaneously particle image velocimetry (PIV) and pulsed shadowgraphy techniques (PST). Experiments were made with water and aqueous glycerol solutions covering a wide range of viscosities (1 × 10 -3 Pa s <  < 1.5 Pa s), in an acrylic column of 32 mm ID. Different wake structures (laminar, transitional and turbulent) are identified, in both stagnant and co-current flow conditions. In stagnant liquids, the wake flow pattern is only dependent on the dimensionless group N f . The different types of wakes obtained are in accordance with the critical N f numbers proposed in previous works. For co-current flow conditions, the flow patterns in the wake depend on the Reynolds number based on the relative (to the bubble) average velocity of the upward liquid flow, the laminar-transitional and transitional-turbulent limits being for the first time experimentally determined. The wake flow patterns are quantified by means of instantaneous and average flow fields. Values for the wake length and wake volume are also presented and compare well with correlations found in literature. Study of the flow in the near-wake zone enabled determination of the distance needed to recover the undisturbed liquid velocity profile. The detailed study of the flow in the wake and near-wake regions is an important contribution to better understanding the interaction and coalescence mechanisms between Taylor bubbles. The data reported are relevant to the validation of numerical simulation codes in the vertical slug flow regime.  2006 Elsevier Ltd. All rights reserved. Keywords: Fluid mechanics; Multiphase flow; Slug flow; Bubble; Wakes; Particle image velocimetry (PIV) 1. Introduction Slug flow is one of several gas–liquid flow regimes occurring inside pipes over a wide range of gas and liquid flow rates. In vertical flow, this pattern is characterized by long bullet-shaped bubbles, also called Taylor bubbles or gas slugs, which almost fill the pipe cross-section. Liquid moves around the bubbles and in the bulk between two successive gas slugs. The liquid moving around the bubble expands at the rear of the bubble, inducing a recirculating liquid wake. ∗ Corresponding author. Tel.: +351 22 508 1645; fax: +351 22 508 1449. E-mail addresses: nogueira@fe.up.pt (S. Nogueira), riethmuller@vki.ac.be (M.L. Riethmuller), jmc@fe.up.pt (J.B.L.M. Campos), apinto@fe.up.pt (A.M.F.R. Pinto). 0009-2509/$ - see front matter  2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2006.08.002 Slug flow is found in many industrial applications, including hydrocarbon production in oil wells and their transportation in pipelines, nuclear reactors during emergency core cooling, power station steam boilers, transport and handling of cryo- genic fluids, gas absorption units, heat exchangers, and air-lift reactors. A great amount of research has been devoted to the study of this two-phase flow regime (Dumitrescu, 1943; Moissis and Griffith, 1962; Nicklin et al., 1962; White and Beardmore, 1962; Brown, 1965; Wallis, 1969; Collins et al., 1978; Fernan- des et al., 1983; Campos and Guedes de Carvalho, 1988a,b; Mao and Dukler, 1991; Barnea and Brauner, 1993; DeJesus et al., 1995; Pinto and Campos, 1996; Pinto et al., 1998, 2001; Bugg and Saad, 2002; van Hout et al., 2002; Viana et al., 2003; Funada et al., 2005; Nogueira et al., 2006; Taha and Cui, 2006, Please cite this article as: S. Nogueira et al., Flow patterns in the wake of a Taylor bubble rising through vertical columns of stagnant and flowing Newtonian liquids: An experimental..., Chemical Engineering Science (2006), doi: 10.1016/j.ces.2006.08.002