Flow regime maps

Two-phase flow characteristics of capillaries are known to be significantly different from the characteristics of larger channels, and consequently the existing vast literature associated with the phenomenology of change-of-phase heat transfer and two-phase flow hydrodynamic processes generally do not apply to capillaries. 

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- 

Furthermore, when d is smaller than the right-hand side of the above equation, the flow transition criterion is, according to Barnea et al. (1983)  

The criterion of Barnea et al. (1983) predicts well flow patterns of air and water in channels several millimeters in diameter. For smaller channels, however, the criteria of Taitel and Dukler (1976) and Barnea et al. (1983) are not suitable. 

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Figure 26. Flow regime map for horizontal gas and liquid flows (D - droplet X - stratification M - mixed B - bubble).

Fig. 2.36 Flow regime map for parallel micro-channels. Region A is the low-heat flux region, and region B the high-heat flux region. Reprinted from Hetsroni et al. (2003b) with permission...

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... 

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. 

This flow regime map can be compared with other maps developed previously for air-water two-phase flow in small-diameter horizontal and vertical channels. Figure 5.21a-d shows comparisons with the results of Damianides and Westwa-ter (1988), Fukano and Kariyasaki (1993), Triplett et al. (1999a) and Zhao and Bi (2001 a), respectively. The solid lines represent the flow regime transition boundaries observed in the 1 mm diameter channels and the flow regime names in parentheses are those given by the respective authors. 

Fig. 5.20 Two-phase flow regime map for a 100 pm micro-channel. Reprinted from Kawahara et al. (2002) with permission...

Fig. 5.21a-d Comparison of two-phase flow regime maps presented by Kawahara et al. (2003) with (a) Damianides and Westwater (1988), (b) Fukano and Kariyasaki (1993), (c) Triplett et al. (1999a) and (d) Zhao and Bi (2001a). Reprinted from Kawahara et al. (2002) with permission... 

In Fig. 5.39a-d the local heat transfer coefficients derived in the horizontal tube are compared to those obtained in the 8° upward inclined pipe and presented by Hetsroni et al. (2006). The results show a clear improvement of the heat transfer coefficient with the pipe inclination. Taitel and Dukler (1976) showed that the flow regimes are very sensitive to the pipe inclination angle. In the flow regime maps presented in their work, the transition from stratified to annular flow in the inclined tube occurs for a smaller air superficial velocity than for the case of the horizontal tube. 

Experimental data on flow patterns and the transition boundaries are usually mapped on a two-dimensional plot. Two basic types of coordinates may be used for the flow regime maps - one that uses dimensional coordinates such as superficial velocities, and another that uses some kind of dimensionless group. Di-... 

Bell, K. J., Taborek, J. and Fenoglio, F. (1970) Chem. Eng. Prog. Symp. Ser. No. 102, 66,154. Interpretation of horizontal in-tube condensation heat transfer correlations with a two-phase flow regime map. 

Figure 3.3 Horizontal flow regime map curves A, B, (Fr) versus Xn curve C, K versus Y curve D, T versus X . (AD, annular dispersed DB, dispersed bubble SW, stratified wavy I, intermittent SS, stratified smooth.) (From Taitel and Dukler, 1976b. Copyright 1976 by American Institution of Chemical Engineers, New York. Reprinted with permission.)...

Figure 3.9 Comparison of flow regime maps at high pressures.

Particular conditions may occur for two-phase downflows in vertical or inclined channels (ducts) that are not completely described by the flow regime maps. Flooding occurs as the rising vapor completely blocks descending liquid. With lowering velocities of the vapor phase, this condition is preceded by the phenome-... 

Figure 3.13 Liquid metal -gas two-phase flow regime map. [From Michiyoshi et al 1986. Copyright 1986 by Hemisphere Publishing Corp., New York. Reprinted with permission.)...

Figure 15-6 Flow regime maps for (a) horizontal and (b) vertical gas-liquid flow, (a, From Baker, 1954 b, from Hewitt and Roberts, 1969.)...

The best known flow regime map for horizontal gas-liquid flow was given by Baker (1954) and is shown in Figure 7.4. Here Gg, GL denote the superficial mass fluxes of the gas and the liquid. For the gas... 

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