Prediction of flow patterns

Most of the data used for constructing such maps have been obtained with the air-water system at or nem atmospheric conditions. Although, intuitively, one might expect the physical properties of the two phases to play important roles in determining the transition from one flow pattern to another, it is now generally 

In vertical flow, gravity acts in the axial direction giving symmetry across the pipe cross-section. Flow patterns tend to be somewhat more stable, but with 

The only study dealing with the vertical two-phase flow in which the liquid is shear-thinning is that of Khatib and Richardson [1984] who worked with suspensions of china clay. Their results compare closely with the predictions of Taitel et al. [1980] for air-water mixtures and this suggests that the transition boundaries between the various flow pattern are largely unaffected by the rheology of the liquid and that Figine 4.3 can be used when the liquid, is shear-thinning. However, no such information is available for visco-elastic liquids. 

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Approximate prediction of flow pattern may be quickly done using flow pattern maps, an example of which is shown in Fig. 6-2.5 (Baker, Oil Gas]., 53[12], 185-190, 192-195 [1954]). The Baker chart remains widely used however, for critical calculations the mechanistic model methods referenced previously are generally preferred for their greater accuracy, especially for large pipe diameters and fluids with ysical properties different from air/water at atmospheric pressure. In the chart. 

Eaton, Ben A., el al., The Prediction of Flow Patterns, Liquid Holdup and Pressure Losses Occurring During Continuous Tw o-Phase Flow in Horizontal Pipelines. /. Petrol. TechnoL, June 1967, pp. 315-328. 

Additional research on the prediction of flow patterns is a necessity, for until detailed stability criteria are developed for the transition from one flow pattern to another, there is no alternative to the empirical flow pattern charts. Some progress in theoretically defining the transition from stratified to wavy or slug flow has been made by Russell and Etchells (R3). Inaccuracy and uncertainty in flow pattern prediction makes estimation of the in situ hydrodynamic quantities and the rate of heat transfer a difficult task. 

Apparently no attempts have been made to prepare a complete chart for the prediction of flow patterns in vertical flow, analogous to Fig. 4. Kozlov (K5) has stated, on the basis of his experiments with air and water in a 1-in. diameter tube, that the flow pattern can be defined by plotting the volumetric gas fraction fed and the average Froude number, Vii /gD- He gives equations for the boundary lines between types of flow (assumed to be straight lines on a log-log plot of the type suggested). 

Dhotre MT, Joshi JB (2004) Two-Dimensional CFD Model for the Prediction of Flow Pattern, Pressure Drop and Heat Transfer Coefficient in Bubble Column Reactors. Chemical Engineering Research and Design 82(A6) 689-707. 

External Flow (Shell Side). Two-phase flow patterns for flow normal to tube bundles (crossflow), such as on the shell side of a shell-and-tube heat exchanger, are much more complex than those inside a plain circular tube. Consequently, prediction of flow patterns in such situations is very difficult. It is important to note that two-phase shellside flow patterns are substantially less analyzed than those for internal flows. A review of the shellside flow pattern is presented by Jensen [68]. The dominant flow patterns (see Fig. 17.51 [69]) may be assessed... 

For two-phase cocurrent gas-liquid flow, there is the wide variety of possible flow patterns which are governed principally by the physical properties (density, surface tension, viscosity of gas, rheology of liquid), input fluxes of the two phases and the size and the orientation of the pipe. Since the mechanisms responsible for holdup and momentum transfer (or frictional pressure drop) vary from one flow pattern to another, it is essential to have a method of predicting the conditions under which each flow pattern may occm. Before developing suitable methods for the prediction of flow pattern, it is important briefly to define the flow patterns generally encountered in gas-liquid flows. Horizontal and vertical flows will be discussed separately as there are inherent differences in the two cases. 

Kashid, M., Kiwi-Minsker, L. (2011). Quantitative prediction of flow patterns in liquid-liquid flow in micro-capillaries. Chemical Engineering and Processing Process Intensification, 50, 972-978. 

Liquid-liquid flows in small channels are quite challenging due to the wide variation of physical properties of the two phases. It was found that hydrodynamics in small scale channels are strongly related to the performance of the reactor. The first step would be to develop accurate predictive tools for the hydrodynamics within the small scale devices. The generation of a unified theory for the prediction of flow patterns, which should be independent of the fluid and the microchannel characteristics and correlate the flow regimes using the relative forces responsible as well as the smface properties, should be investigated with more parametric studies. The absence of this kind of theory lies on the fact that most investigations have... 

N. Brauner, A. Ullmann, 2006, The prediction of flow pattern maps in mini channels, in 44th European Two-phase Flow Group Meeting, EPFL, Lausanne. 

There have been efforts at simulating flow in the machine notably by Canedo and Valsamis [210], Kim and White [212], and Bang and White [213]. Predictions of flow patterns on the rotors and the pressure profiles for fully filled machines are shown in Fig. 9.33. 

Dhotre MT, Joshi JB (2004) Two-dimensional CFD model for the prediction of flow pattern,... 

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