Flow pattern map

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. 

Figure 24. Example of flow pattern map for air water system in horizontal pipes.

Consideration will now be given to the various flow regimes which may exist and how they may be represented on a Flow Pattern Map to the calculation and prediction of hold-up of the two phases during flow and to the calculation of pressure gradients for gas-liquid flow in pipes. In addition, when gas-liquid mixtures flow at high velocities serious erosion problems can arise and it is necessary for the designer to restrict flow velocities to avoid serious damage to equipment. 

The regions over which the different types of flow can occur are conveniently shown on a Flow Pattern Map in which a function of the gas flowrate is plotted against a function of the liquid flowrate and boundary lines are drawn to delineate the various regions. It should be home in mind that the distinction between any two flow patterns is not clear-cut and that these divisions are only approximate as each flow regime tends to merge in with its neighbours in any case, the whole classification is based on highly subjective observations. Several workers have produced their own maps 4 8. ... 

The principal flow patterns are shown in Figure 5.1. In general, the flow pattern map (Figure 5.2) is also applicable to vertical flow. Further reference to flow of gas- liquid mixtures in vertical pipes is made in Section 8.4.1 with reference to the operation of the air-lift pump. 

Mandhane, J. M., Gregory, G. A. and Aziz, K. Inti. JL Multiphase Flow l (1974) 537-553, A flow pattern map for gas-liquid flow in horizontal pipes. 

Two-phase flow pattern maps, observed by Revellin et al. (2006), are presented in Fig. 2.31 in mass flux versus vapor quality, and superficial liquid velocity versus superficial vapor velocity formats calculated from the test results as follows ... 

Notably, the higher the mass flux, the earlier annular flow is reached. Bubbly flow is more or less non-existent for mass fluxes exceeding 1,000 kg/m s. The most important observation about the flow patterns is that their transitions are controlled primarily by the rate of coalescence, which is not recognized as a contributing factor by any of the micro-scale or macro-scale flow pattern maps. 

Fig. 2.31a,b Flow pattern maps with experimental transition lines for R-134a, d = 0.5 mm, 70 mm, Ts = 30 °C and AFsub = 3 K. Reprinted from Revellin et al. (2006) with permission... 

Fig. 5.17 Adiabatic micro-channel two-phase flow pattern map. Reprinted from Qu et al. (2004) with permission...

There has been relatively little work done on the development of two-phase flow regime maps for micro-channels. The general trends of how the transition lines are shifted as the diameter is decreased are unclear. Figure 5.19 shows a flow pattern map obtained for air-water two-phase flow in a 20 pm i.d. silica tube by Serizawa et al. (2002) at nearly atmospheric pressure. 

Two-phase flow in parallel micro-channels, feeding from a common manifold shows that different flow patterns occur simultaneously in different microchannels. The probability of appearance of different flow patterns should be taken into account for developing flow pattern maps. 

Rezkallah KS (1996) Weber number based flow-pattern maps for liquid-gas flows at microgravity. Int J Multiphase Flow 22 1265-1270... 

The advantage of the dispersing principle is related to the relatively low technical expenditure to achieve dispersion, i.e. the simplicity of the concept. However, as flow patterns may change and are not known for new systems, they have to be identified, documented as flow-pattern maps and controlled. Thus, some analytical characterization has to be done in advance of the experiment. Hence inspection windows again are essential (for the first prototype they may be eliminated later). 

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].

The cyclohexene hydrogenation is a well-studied process especially in conventional trickle-bed reactors (see original citations in [11,12]) and thus serves well as a model reaction. In particular, flow-pattern maps were derived and kinetics were determined. In addition, mass transfer can be analysed quantitatively for new reactor concepts and processing conditions, as overall mass transfer coefficients were determined and energy dissipations are known. In lieu of benchmarking micro-reactor performance to that of conventional equipment such as trickle-bed reactors, such a knowledge base facilitates proper, reliable and detailed comparison. 

The reaction is carried out using a Pt/Al203 catalyst [11,12]. Information on this reaction when conducted in trickle-bed reactors is available, comprising flow-pattern maps, kinetic data, mass transfer data and energy dissipation data (see original citations in [11]). 

Figure 3.15 Generalized flow pattern map boiling in horizontal tubes. (From Dukler and Taitel, 1991b. Copyright 1991 by University of Houston, Houston, TX. Reprinted with permission.)...

Baker (Bl) developed a flow pattern map for horizontal gas-liquid systems that is shown in Fig. 5. The coordinates are functions of gas and liquid mass flow rates, phase densities, liquid viscosity, and surface tension. Using the same coordinates, Cichy et al. (C5) have presented a modification of the flow-pattern maps of Govier and co-workers (B6, G2, G3) for vertical gas liquid systems. 

Fig. 4. Suggested flow pattern map for horizontal cocurrent flow (modified from that of Baker).

Fig. 5a. Flow pattern map for vertical air-water flow [as proposed by Griffiths and Wallis (G8)l.

Figure 7 Flow pattern maps for cocurrent air-water upflow through motionless mixers. (From Ref. 8.)... 

The most reliable methods for fully developed gas/liquid flows use mechanistic models to predict flow pattern, and use different pressure drop and void fraction estimation procedures for each flow pattern. Such methods are too lengthy to include here, and are well suited to incorporation into computer programs commercial codes for gas/liquid pipeline flows are available. Some key references for mechanistic methods for flow pattern transitions and flow regime-specific pressure drop and void fraction methods include Taitel and Dukler (AIChEJ., 22,47-55 [1976]), Barnea, et al. (Int. J. Multiphase Flow, 6, 217-225 [1980]), Barnea (Int. J. Multiphase Flow, 12, 733-744 [1986]), Taitel, Barnea, and Dukler (AIChE J., 26, 345-354 [1980]), Wallis (One-dimensional Two-phase Flow, McGraw-Hill, New York, 1969), and Dukler and Hubbard (Ind. Eng. Chem. Fun-dam., 14, 337-347 [1975]). For preliminary or approximate calculations, flow pattern maps and flow regime-independent empirical correlations, are simpler and faster to use. Such methods for horizontal and vertical flows are provided in the following. 

The double-pipe mixer was designed and so far only used for contacting and reacting immiscible fluids [134], The respective flow-pattern maps were derived and annular and slug flows as well as complete spread of the inner-tube fluid were identified as distinct regimes. Since in this chapter only miscible liquids are concerned, no protocol and no results are given for the mixer below. H owever, the device is mentioned, since it could in principle be used also for mixing miscible fluids. 

Figure 1.142 A kind of flow-pattern map for zig-zag micro mixers of various dimensions correlating their Reynolds numbers with their hydrodynamic regimes as a function of their ratio of bend length to hydraulic diameter [151]...

Based on these experiments, a kind of flow-pattern map was proposed describing a region of laminar flow where viscous losses dominate, an intermediate region with secondary flow where inertial losses dominate (albeit still not turbulent) and a region of fully developed turbulent flow (see Figure 1.142) [151]. The transitional Reynolds number from the pure laminar to the secondary-flow regime increases with the ratio of bend length to hydraulic diameter. 

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