Gas-liquid slug flow

Dukler, A. E., and M. G. Hubbard, 1975, A Model for Gas-Liquid Slug Flow in Horizontal and Near Horizontal Tubes, Ind. Eng Chem. Fundam. 14(4) 337. (3)... 

Mercier M, Maranges C, Fonade C, and Lafforgue-Delorme C, Flux enhancement using upward gas liquid slug flow Application to continuous alcoholic fermentation with cell recycle. Biotech. Bioeng. 1998 58 47. 

Dukler, A.E., Hubbard, M.G. (1975). A model for gas-liquid slug flow in horizontal and near horizontal tubes. Journal of Industrial Engineering and Chemistry 14(4) 337-347. 

Walsh PA, Walsh EJ, Muzychka YS (2010) Heat transfer model for gas-liquid slug flows under constant flux. Int J Heat Mass Transf 53(15) 3193-3201... 

A microreaction system was developed for the carbonylation of nitrobenzene as well [28]. Under lower CO gas pressure [9.5 bar much lower than those in conventional ones (>100 bar)], phenylisocyanate was produced. A gas-liquid slug flow of the reactant mixture was formed in the microchannel for efficient mass transfer across the gas-liquid interfaces. The isocyanate yield of the microflow reaction was shown to be three to six times higher than that of the batch reaction, depending on the inner diameter (i.d.) of the microtube. A higher isocyanate yield was obtained in a narrow-bore tube (0.5 mm i.d.) than in a wide-bore tube (1.0 mm i.d.). The catalyst they applied was Pd(py)2Cl2 and pyridine system. 

Figure12.8 Gas-liquid slug flow for constant flow rate and various slug lengths. (Adapted from Ref. [51].)...

Street JR, Tek MR (1965) Dynamics of bullet shaped bubbles encountered in vertical gas liquid slug flow. AIChE J ll(4) 644-650... 

Figure 16 Relative increase of friction and mass transfer due to gas-liquid Taylor flow, compared to developed laminar flow in small tubes. represents the dimensionless length of a liquid slug. Re the Reynolds number based on the liquid.

Segmented gas-liquid (Taylor) flow was used for particle synthesis within the liquid slugs. Tetraethylorthosilicate in ethanol was hydrolyzed by a solution of ammonia, water and ethanol (Stober synthesis) [329]. The resulting silicic acid monomer Si (OH)4 is then converted by polycondensation to colloidal monodisperse silica nanoparticles. These particles have industrial application, for example, in pigments, catalysts, sensors, health care, antireflective coatings and chromatography. 

In cocurrenf gas-liquid flow, several flow regimes can occur. The preferred one usually is Taylor flow. This type of flow is characterized by gas bubbles and liquid slugs flowing consecutively through the small monolith charmels. The gas bubbles occupy (nearly) the whole cross section of fhe channel and are elongated. Only a thin liquid film separates the gas bubbles from fhe catalyst (Figure 13). 

Identical to gas-liquid Taylor flow, the mass transfer in liquid-liquid slug flow has two contributions film and slug caps. The specific interfacial area, ratio of surface area of the slug per unit its volume, can be written by neglecting the film thickness as... 

There are two fundamental differences between gas-liquid and liquid-liquid slug flow in microchannels [37]. 

In the liquid-liquid slug flow system, because of close physical properties of both fluids it might be possible that there is no wall film and both fluids flow alternatively through the capillary this is not observed in gas-liquid systems. 

Figure 11.3 Different mass transfer mechanisms in gas—liquid segmented flow (Taylor flow) (1) from the bubble to the recirculation region in a liquid segment (slug), (2) between a bubble and the microchannel wall...

Intermittent (I) - In this flow pattern the liquid inventory in the pipe is non-uniformly distributed axially. Plugs or slugs of liquid that fill the pipe are separated by gas zones that contain a stratified liquid layer flowing along the bottom of the... 

Hughmark, G. A., Holdup and Heat Transfer in Horizontal Slug Gas-Liquid Flow, Chem. Eng. Sci., 20, 1964, p. 1007. 

A knowledge of hold-up is particularly important for vertical flow since the hydrostatic pressure gradient, which is frequently the major component of the total pressure gradient, is directly proportional to liquid hold-up. However, in slug flow, the situation is complicated by the fact that any liquid which is in the form of an annular film surrounding the gas slug does not contribute to the hydrostatic pressure 14. ... 

Figure 8.43. Liquid holdup 6/ and gas holdup g ( = 1 — ft) for slug flow in a 25 mm diameter pipe as a function of superficial gas velocity (u< ) and superficial liquid velocity ( /)...

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. 

From the experimental observation it is quite clear that the occurrence of the slug flow is rather an entrance phenomenon than one induced from the tube. Slug flow occurs if the speed of long gas bubbles is not high enough to overcome the strong surface tension force of the liquid bridge between them (Fig. 5.6b). 

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