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Two-Phase Flow Dynamics
Published in Neil E. Todreas, Mujid S. Kazimi, Nuclear Systems Volume I, 2021
Neil E. Todreas, Mujid S. Kazimi
The flow regimes identified in vertical flows are the bubbly, slug, churn and annular regimes (Figure 11.2). The bubbly regime is identified by the presence of dispersed gas bubbles in a continuous liquid phase. The bubbles can be of variable size and shape. Bubbles of 1 mm or less are spherical, but larger bubbles have variable shapes. Slug flow is distinguished by the presence of gas plugs (or large bubbles) separated by liquid slugs. The liquid film surrounding the gas plug usually moves downward. Several small bubbles may also be dispersed within the liquid. The churn flow is more chaotic but of the same basic character as the slug flow. Annular flow is recognizable from the presence of a continuous core of gas surrounded by an annulus of the liquid phase. If the gas flow in the core is sufficiently high, it may be carrying liquid droplets. In this case, an annular-dispersed flow regime is said to exist. Hewitt and Roberts [32] also suggested that the droplets can gather in clouds forming a wispy-annular regime. The liquid droplets are torn from the wavy liquid film, get entrained in the gas core and can be de-entrained to join the film downstream of the point of their origin.
Mass Transfer: Membrane Processes
Published in Shyam S. Sablani, M. Shafiur Rahman, Ashim K. Datta, Arun S. Mujumdar, Handbook of Food and Bioprocess Modeling Techniques, 2006
David Hughes, Taha Taha, Cui Zhanfeng
Gas sparging, i.e., injecting air bubbles into the liquid feed to generate a two-phase flow stream, has been investigated for nearly a decade.36 Pioneering work dates back to the first implementation of such a technique for UF by Cui in 1993. When gas and liquid flow together in a tube, a slug flow pattern often exists. Such a flow pattern is characterised by a quasiperiodic passage of long roundnosed bubbles—usually referred to as “Taylor bubbles,” or “slugs”—separated by liquid plugs. In particular, for UF, it was found that the gas flow rate required to effect substantial improvements in permeate flux is very small. Furthermore, the liquid crossflow velocity has little effect on the permeate flux in gas-sparged UF. These two aspects of the technique mean there exists the possibility of significant savings on energy costs.37 Therefore, it not surprising that numerous works have been dedicated to studying the development of the concentration polarization and techniques to lessen such a phenomenon. In their succinct paper, Kleinstreuer and Belford38 reviewed early works on approximate one-and two-dimensional models. In the 1990s, computational fluid dynamics (CFD) became an attractive tool for researchers to simulate pressure driven membrane processes. The adoption of CFD revealed a detailed picture of the process and proved helpful in optimizing filtration processes.
Assessment of well trajectory effect on slug flow parameters using CFD tools
Published in Chemical Engineering Communications, 2020
Esteban Guerrero, Andres Pinilla, Nicolas Ratkovich
Gas–liquid slug flow is one of the most common multiphase flow patterns. It is encountered in many industrial applications such as oil and gas pipelines, distillation columns, nuclear reactors, membrane processes, chemical reactors, and power plants with a direct steam generation (Yasukawa et al., 2011; Abdulkadir et al., 2013; Wei et al., 2013; Wang et al., 2014; Hoffmann et al., 2016). Although two-phase slug flow is often encountered, it may enhance or deteriorate the process due to its hydrodynamics. For example, slug flow condition increases the heat and mass transfer properties benefitting separation and reaction processes (Ratkovich et al., 2011; Bandara et al., 2015). On the other hand, slug flow could accelerate the corrosion process in pipelines or cause vibration conditions. Also, it could cause undesired effects on surface and downhole equipment typically used in the oil and gas industry, such as early failure and more substantial maintenance periods (Pagano et al., 2009; Araújo, et al. 2013).
Internal two-phase flow induced vibrations: A review
Published in Cogent Engineering, 2022
Samuel Gebremariam Haile, Elmar Woschke, Getachew Shunki Tibba, Vivek Pandey
As stated earlier, the flow regime has a distinct effect on FIV. In bubbly flows, a source of two-phase FIV is bubble-induced vibration. This is distinct from momentum-induced vibrations since momentum changes are not considered significant for bubbly flows. Similarly, momentum fluctuations have been found to be significant in the slug-flow regime. Slug flow occurs in internal two-phase flows, with a distinct separation between the phases, and liquid “slugs” alternate with gas-phase “Taylor bubbles” in the flow. As a consequence, the fluctuations in density are clear and pronounced for the slug flow regime. Momentum fluctuations are found to be significant in the case of pipe bends, where the centrifugal force component adds to the force fluctuations.
Void Fraction Measurement of Gas-Liquid Two-Phase Flow Based on Empirical Mode Decomposition and Artificial Neural Networks
Published in Heat Transfer Engineering, 2019
Weiwei Wang, Khellil Sefiane, Gail Duursma, Xiao Liang, Yu Chen
Based on one DP signal, the void fraction prediction errors for slug flow are a little larger than that for the other two flow patterns. Gas–liquid slug flow is one of the most complex flow patterns. Liquid slugs, small bubbles, and large bubbles are heterogeneously distributed in the flow pipeline. The small bubbles coalesce into a large bubble and a large bubble may also be broken into many small bubbles, causing interface changes and complicated interaction between liquid and gas phases. It is generally thought that slug flow can result in severe fluctuations of void fraction and pressure drop in the pipeline. Therefore, it is difficult to predict the void fraction depending only on one DP signal.