Slug Bubbly Flow

Slug flow is a flow of a series of slugs (plugs) of one phase separated by the other Each slug serves as an individual processing subvolume. In liquid-liquid systems, one phase acts as continuous while other discrete Mass transport is because of convection within each slug and diffusion between two adjacent slugs 

Relatively higher interfacial area, which can be changed in a given reactor by varying the flow rates 

Intensity of internal circulations increases with flow and thus diffusive penetration between two phases Downstream separation is difficult 

Relatively low interfacial area and is constant in a given microchannel 

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In their studies of three-phase capillary air slug (bubble) flow, Stebe and Maldarelli [47] correlated surfactant concentration to equivalent flow rate invoking similar reasoning. At a higher surfactant concentration, flow rate increased with surfactant concentration, due to the relief of surface tension gradients at the air bubble surface. When using protein-based surfactants, retardation of flow due to surface viscous effects (flow rate decreased with an increase in protein concentration) was observed. 

Condensation in Microchanneis, Figure 5 Flow patterns of annular flow and slug/bubbly flow in a microchannel [7]... 

Slug Slugs of gas bubbles flowing through the liquid... 

The first flow pattern zone corresponds to the isolated bubble (IB) regime where the bubble generation rate is much higher than the coalescence rate. It includes both bubbly flow and/or slug flows and is present up to the onset of coalescence process domination. The second zone is the coalescing bubble (CB) regime, which is... 

At relatively low liquid superficial velocities, increasing the mixture volumetric flux led to longer bubbles and shorter liquid slugs, eventually leading to the merging of elongated bubbles, and the development of the slug-annular flow pattern, repre-... 

As more air was added to the channel, the slug flow became unstable, the slug bubble broke down, and eventually the churn flow occurred in the channel. As shown in Fig. 5.3d, the most significant feature of flow characteristics in the churn flow is that the pressure oscillated at a relatively high amplitude, since the gas plug and liquid bridge flowed through the test section alternatively. 

For all flow conditions tested in that study, a bubbly flow pattern with bubbles much smaller than the channel diameter (100 pm) was never observed. While liquid-only flows (or liquid slugs) containing small spherical bubbles were not observed, small droplets were observed inside gas core flows. Furthermore, no stratified flow occurred in the micro-channel as reported in previous studies of two-phase flow patterns in channels with a diameter close to 1 mm (Damianides and Westwater 1988 Fukano and Kariyasaki 1993 Triplett et al. 1999a Zhao and Bi 2001a). 

Suo and Griffith (1964) performed experiments in horizontal channels with 0.5 and 0.7 mm diameters, and could identify slug, slug-bubbly, and annular flow patterns. For transition from slug to slug-bubbly, they suggest ReWe = 2.8 x 10, where Re = We = dpildljla, = 1. 2(Gls + 1/gs)- Re and We rep-... 

The flow regime maps shown in Fig. 5.16a,b indicate that typical flow patterns encountered in the conventional, large-sized vertical circular tubes, such as bubbly flow, slug flow, churn flow and annular flow, were also observed in the channels having larger hydraulic diameters ([Pg.216]

Figure 5.16c indicates that as the channel size was reduced to Jh = 0.866 mm, the dispersed bubbly flow pattern vanished from the flow regime map. Figure 5.16a-c indicates that the slug-churn flow transition line shifted to the right, as the channel size was reduced. Similar trends were also found in small circular tubes by the... 

Figure 5.6 Flow pattern map for a gas/liquid flow regime in micro channels. Annular flow wavy annular flow (WA) wavy annular-dry flow (WAD) slug flow bubbly flow annular-dry flow (AD). Transition lines for nitrogen/acetonitrile flows in a triangular channel (224 pm) (solid line). Transition lines for air/water flows in triangular channels (1.097 mm) (dashed lines). Region 2 presents flow conditions in the dual-channel reactor ( ), with the acetonitrile/nitrogen system between the limits of channeling (I) and partially dried walls (III). Flow conditions in rectangular channels for a 32-channel reactor (150 pm) (T) and singlechannel reactor (500 pm) (A) [13].

However, in contrast to the dispersive mixers forming slug and aimular flow patterns, here the flow-fhrough channel is much larger than the typical dimensions of the dispersed phase (compare with Section 5.1.2). As a result, bubbly flows and foams are the common flow patterns. 

Figure 3.5 Flow regimes in vertical downflow (A) bubbly flow (B) slug flow (C) falling film flow (D) bubbly falling film flow (E) chum flow (F) dispersed annular flow. (From Oshimowo and Charles, 1974. Copyright 1974 by Canadian Society of Chemical Engineers, Ottawa, Ont. Reprinted with permission.)...

Pattern transition in vertical adiabatic flow. Upward vertical flow has been studied intensively, both because of the simplicity of the geometric condition and the relevance in applications. The map shown in Figure 3.4 is the result of rather recent and relevant studies into the interpretation of regime transition mechanisms. In this figure, the transition between bubbly flow and slug flow occurs be-... 

The first model is more suited to dealing with mixed flow such as bubble flow and slug flow, while the second is more suited to cases where flow is separated, as in stratified and annular flow. 

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