Slug flow transient

In gas-liquid two-phase flow, several flow patterns exist such as bubbly, slug, plug, and annular flow depending on the pipe configuration, geometry, and flow conditions. Of these types of flows, slug flow is one of the most complex, owing to its intermittent and transient nature. Despite its complexity, industrial processes often require an online, accurate, and noninvasive estimation of such flow. If this is accomplished, industrial processes can be kept within acceptable quality limits and additionally, financial losses may be reduced. 

Using the slug-flow model, show that the boundary-layer energy equation reduces to the same form as the transient-conduction equation for the semi-infinite solid of Sec. 4-3. Solve this equation and compare the solution with the integral analysis of Sec. 6-5. 

It is concluded that thermodynamic equilibrium cannot exist in film boiling and transitional regimes during cool-down. Although this is generally expected, the extent of the departure from vapor-liquid equilibrium was previously unknown. This departure from equilibrium and the occurrence of mist and slug flows during cool-down have provided a means for the determination of vapor fractions under transient, nonisothermal conditions. 

This map has been checked by many researchers, indicating that it is applicable to a wide range of conditions. Also shown in Figure 3.4 are correlations derived by Mishima and Ishii (1984), which used similar basic principles except for the slug-to-churn transition. These authors pointed out that, in view of the practical applications of the separate-fluid model to transient analysis, flow regime criteria based on the superficial velocities of the liquid and gas may not be consistent with the separate-flow model formulation. A direct geometric parameter such as the... 

Figure 4. Transient responses to slug (left) and step (right) inputs of reactant for first order reaction and selected kr values. The flow has the same residence time distribution as two perfectly mixed vessels in sequence. For slug input, c0 = m /V.

Figure 6. Transient responses at two consecutive downstream stations 4 and 6 to the same slug inputs of reactant undergoing first order reaction. The flow is a stretch of natural stream for which the responses to inert tracer (k = 0) are empirical (2). c0 = m/V.

Nakoryakov, V.E. Pokusaev, B.G. Pribaturin, N.A. Lezhnin, S.I. Press l e Ware Dsmamics in slug regime of gas-liquid flow. Int. Seminar "Transient Phenomena in Multiphase Plow". Dubrovnik, Yugoslavia, 1987. 

In multiphase microfiuidics, transient phenomena can be divided into fluctuations that are flow induced (inside the channel) and induced by external fluctuations. Kraus et al. [69] measured statistical properties (distribution of liquid slug and gas bubble lengths) in segmented gas-liquid flow and documented the sensitivity to external disturbances (e.g. syringe pump pressure fluctuations). Van Steijn et al. [87] investigated such fluctuations in detail for low-velocity flow in a short... 

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