SPRITE MRI of bubbly flow in a horizontal pipe Mark Sankey a , Zhi Yang b , Lynn Gladden a , Michael L. Johns a , Derek Lister c , Benedict Newling b, * a Magnetic Resonance Research Centre, Department of Chemical Engineering & Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, UK b UNB MRI Centre, Department of Physics, University of New Brunswick, P.O. Box 4400, 8 Bailey Drive, Fredericton, NB, Canada E3B 5A3 c Department of Chemical Engineering, University of New Brunswick, P.O. Box 4400, Fredericton, NB, Canada E3B 5A3 article info Article history: Received 19 November 2008 Revised 10 January 2009 Available online 1 February 2009 Keywords: Two-phase flow MRI SPRITE Velocimetry Turbulence abstract Bubble flow is characterised by numerous phase interfaces and turbulence, leading to fast magnetic res- onance signal decay and artefacts in spin-warp imaging. In this paper, the SPRITE MRI pulse sequence, with its potential for very short encoding times, is demonstrated as an ideal technique for studying such dynamic systems. It has been used to acquire liquid velocity and relative intensity maps of two-phase gas–liquid dispersed bubble flow in a horizontal pipe at a liquid Reynolds number of 14,500. The fluids were air and water and a turbulence grid was used to generate a dispersed bubble flow pattern. The SPRITE technique shows promise for future research in gas–liquid flow. Ó 2009 Published by Elsevier Inc. 1. Introduction 1.1. Gas–liquid two-phase pipe flow Two-phase gas–liquid flow occurs in many situations of theo- retical and practical interest. One of the most common geometries is pipe flow, particularly in hydrocarbon processing, boilers and cooling systems. As with all multiphase flows it is a complex phe- nomenon and current measuring and modelling capabilities are limited; consequently there are presently no generally applicable CFD codes available [1]. The online measurement of bulk flow rates alone in such systems is difficult and measuring local phase distri- butions and velocities is even more challenging. There is a need for techniques that can measure local parameters for two reasons: first, to improve our fundamental understanding of gas–liquid flow; and second, to validate CFD codes. Major motivations for studying such systems are to learn how different phase and veloc- ity distributions influence pressure drop and corrosion. The fundamentals of gas–liquid flow are presented here but a more comprehensive account can be found in standard texts, for example Perry et al. [2] and Coulson et al. [3]. The distribution of phases in gas–liquid flow depends on the relative flow rates, fluid properties and geometries, and can be classified into a number of distinct patterns or flow regimes. Gravity causes the less dense gas phase to rise (buoyancy); therefore the direction of gravity rel- ative to the flow axis means that vertical and horizontal pipe flows exhibit different behaviour and in the latter the gas phase tends to occupy the upper part of the pipe. As the gas-to-liquid ratio in- creases the gas changes from forming the dispersed phase to the continuous phase. Flow regime definitions are subjective and the transitions between them are gradual, but in general seven flow re- gimes for fully-developed horizontal pipe flow have been identi- fied [4], as illustrated in Fig. 1. They are as follows, in order of decreasing ratio of liquid to gas flow rate: Bubbly flow. The gas is dispersed in the liquid as bubbles which move at a velocity similar to the liquid. This flow regime occurs at high ratios of liquid to gas flow rates, but note that gravita- tional forces will tend to cause the bubbles to concentrate near the top of the pipe at lower liquid velocities and the distribution of bubbles becomes more homogeneous at higher liquid velocities. Plug flow. Alternate plugs of liquid and gas move along the upper part of the pipe. Stratified flow. The liquid and gas flow along the bottom and top of the pipe respectively, with a smooth interface. Wavy flow. This is similar to stratified flow but waves moving in the flow direction are formed at the gas–liquid interface because of higher relative velocities between the phases. Slug flow. Liquid waves touch the top of the surface of the pipe, forming frothy slugs which move at a velocity much greater than the liquid average velocity. Annular flow. Liquid flows as a thin film along the pipe walls and gas flows in the core with some entrained droplets of liquid. Spray, dispersed or mist flow. This is similar to annular flow except nearly all the liquid phase is entrained as small droplets. 1090-7807/$ - see front matter Ó 2009 Published by Elsevier Inc. doi:10.1016/j.jmr.2009.01.034 * Corresponding author. Fax: +1 506 453 4581. E-mail address: bnewling@UNB.ca (B. Newling). Journal of Magnetic Resonance 199 (2009) 126–135 Contents lists available at ScienceDirect Journal of Magnetic Resonance journal homepage: www.elsevier.com/locate/jmr