Chemical Engineering Journal 155 (2009) 326–332 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Rise of Taylor bubbles through narrow rectangular channels S. Bhusan a , S. Ghosh b , G. Das b,∗ , P.K. Das a a Department of Mechanical Engineering, IIT Kharagpur, Kharagpur, West Bengal 721302, India b Department of Chemical Engineering, IIT Kharagpur, Kharagpur, West Bengal 721302, India article info Article history: Received 28 January 2009 Received in revised form 25 June 2009 Accepted 4 July 2009 Keywords: Taylor bubble Rise velocity Two-phase flow Rectangular narrow channel Inclination Orientation abstract Experiments have been performed to investigate the rise of Taylor bubbles in narrow rectangular channels (0.0051 m × 0.0027 m × 0.8 m and 0.01 m × 0.0027 m × 0.8 m). The studies conducted for both stationary and moving liquid have revealed definite influence of channel orientation, dimension and inclination on the propagation velocity of Taylor bubbles. The rise velocity first increases and then decreases as the channel is moved from the horizontal to the vertical position with its broad face always lying in a vertical plane. This is in agreement to the results reported in literature for circular as well as non-circular geometries. On the other hand, the rise velocity increases continuously with inclination when the channel is oriented with its broad face in a horizontal plane. The explanation for this difference in behavior has been obtained through visualization and photographic recording. It has also been noted that the bubble rise velocity in the vertical orientation could not be predicted by any of the existing correlations proposed for non-circular channels. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The recent trend of miniaturization has opened up ample oppor- tunities to use micro-reactor technology for several applications. Miniature reactor offers a number of advantages over the conven- tional design. They are compact, easily controllable and require less fluid inventory as well as less reaction time. Further, the require- ment of scale-up may be absent or at the best minimum in case of these new generation reactors. With this motivation, the last decade has witnessed a number of studies on gas–liquid two-phase flow through mini and micro-channel of circular as well as non-circular cross-section. Almost all the researches have noted the existence of slug flow pattern over a wide range of flow conditions. In a wide tube (D > 10 mm), this regime is usually characterized by the peri- odic appearance of axisymmetric bullet shaped Taylor Bubbles and aerated liquid slugs. In narrow passages, slug flow comprises of a train of axisymmetric elongated Taylor bubbles separated by liquid slugs. This has been termed as “pure slug flow” by Nakoryakov et al. [1]. Since the hydrodynamics of Taylor bubble governs the slug flow pattern, several works both experimental (Dumitrescu [2], Davies and Taylor [3], Zukoski [4], Benediksen [5], Das et al. [6]) and theo- retical (Dumitrescu [2], Davies and Taylor [3], Wallis [7], Bretherton [8], Carew et al. [9]) have been reported on the rise of Taylor bub- bles through stationary and moving liquid columns. However, the ∗ Corresponding author. Tel.: +91 03222 283952; fax: +91 03222 282250. E-mail address: gargi@che.iitkgp.ernet.in (G. Das). majority of the studies are confined to larger tube diameters and only a few works have been reported on small diameter conduits of circular cross-section. Barnea et al. [10] have observed elongated air bubbles in a vertical tube of 4 mm diameter and mentioned it as a limiting case of slug flow. Mishima and Hibiki [11] have studied the slug velocity and other flow characteristics for 1–4 mm diameter vertical tube. They have estimated the rise velocity of slug bubbles using the drift flux model and found the approximate value of dis- tribution parameter to be 1.1. Cheng and Lin [12] have reported slug flow to be the dominant flow regime for gas–liquid flow through tubes of 2–8 mm diameter and noted higher slug rise velocity in inclined tube as compared to the vertical or horizontal configura- tion. They have also reported the shape of gas slugs to change with inclination, tube diameter and gas superficial velocity. Liu et al. [13] have studied the effect of geometry and fluid properties on Taylor bubble rise velocity in vertical capillaries with air as the gas phase and water, ethanol or oil mixture as the liquid phase. In non-circular passages, one of the earliest studies dates back to Maneri and Zuber [14]. They investigated the effect of inclination and fluid properties on the rise of bubbles in a two dimensional tank and reported the influence of fluid properties on the bub- ble rise to be more pronounced at the inclined plane. Sadatomi et al. [15] reported the pressure drop and rise of large air bubbles through water in rectangular, triangular and annular passages and expressed the rise velocity of slug bubbles in still water as: u b = 0.35  gD e (1) where D e is the equi-periphery diameter of the non-circular cross- section. 1385-8947/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2009.07.006