Gasliquid Twophase Pipe Flow

The two-phase flow of gases and liquids has been the subject of literally thousands of publications in the literature, and it is clear that we can provide only a brief introduction to the subject here. Although the single phase flow of liquids and gases is relatively straightforward, the two-phase combined flow is orders of magnitude more complex. Two-phase gas-liquid flows are also more complex than fluid-solid flows because of the wider variety of possible flow regimes and the possibility that the liquid may be volatile and/or the gas a condensable vapor, with the result that the mass ratio of the two phases may change throughout the system.

A. Flow Regimes

The configuration or distribution of the two phases in a pipe depends on the phase ratio and the relative velocities of the phases. These regimes can be described qualitatively as illustrated in Fig. 15-5a for horizontal flow and in Fig. 15-5b for vertical flow. The patterns for horizontal flow are seen to be more complex than those for vertical flow because of the asymmetrical effect of gravity. The boundaries or transitions between these regimes have been mapped by various investigators on the basis of observations in terms of various flow and property parameters. A number of these maps have been compared by Rouhani and Sohal (1983). Typical flow regime maps for horizontal and vertical flow are shown in Figs. 15-6a and 15-6b. In Figures 15-5 and 15-6, Gg = mwG/A is the mass flux of the gas, GL = mml/A is the mass flux of the liquid, and X and $ are fluid property correction factors:

where a is the surface tension and the subscripts W and A refer to water and air, respectively, at 20°C. A quantitative model for predicting the flow regime map for horizontal flow in terms of five dimensionless variables was developed by Taitel and Duckler (1976).

The momentum equation written for a differential length of pipe containing the two-phase mixture is similar to Eq. (15-29), except that the rate of momentum changes along the tube due to the change in

Figure 15-5 Flow regimes in (a) horizontal and (b) vertical gas-liquid flow.

annular

Figure 15-5 Flow regimes in (a) horizontal and (b) vertical gas-liquid flow.

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