Two-phase slug flow

Evaporative two-phase flow in a heated micro-channel resembles a two-phase slug flow with distinct domains of liquid and vapor. These domains are divided by the infinitely thin evaporating front, which propagates relatively to the fluid with a velocity u f equal (numerically) to the linear rate of liquid evaporation. In the frame of reference associated with micro-channel walls, the velocity of the evaporation front is... 

Taitel, Y., and D. Barnea, 1990, Two-Phase Slug Flow, Adv. Heat Transfer 20 83, (3)... 

Bracing of wall stiffeners to allow for possible jet force impingement on the vessel wall, and for intermittent buffeting and vibration if two-phase slug flow can occur. 

Moissis, R. and Griffith, P., Entrance effects in two-phase slug flow, Transactions of AS ME, Journal of Heat Transfer, Series C 84, pp. 29-38 (1962). 

Wambsganss, M. W., Jendrzejczyk, J. A., and France, D. M. (1994) Determination and Characteristics of the Transition to Two-Phase Slug Flow in Small Horizontal Channels, Journal of Fluids Engineering,... 

Two-phase flow patterns in vertical tubes. The liquid flow rate is upward at a small, constant velocity. The gas flow rate upward increases steadily from left to right. The annular pattern shown is often referred to as climbing film flow. [From D. J. Nicklin and J. F. Davidson, The onset of instability in two-phase slug flow, in Symposium in Two-Phase Flow, Institution of Mechanical Engineers, London, 1962. Reproduced by permission j of the publisher.]... 

Fluid-fluid systems are widely used for chemical transformations. Examples are halogenations, hydrogenations, and hydroformylations for gas-liquid reactions and nitrations, polymerizations, and cyclization for liquid-liquid systems. In addition, two-phase slug flow reactors can be used to get narrow residence time distribution at low liquid Reynolds numbers as demonstrated in chapter 3. Most of the reactions mentioned above are highly exothermic and heat evacuation is an important issue for efficient temperature control. 

Torres, A., Hemmelmann, A., Vergara, C., Jeison, D. (2011). Application of two-phase slug-flow regime to control flux reduction on anaerobic membrane bioreactors treating wastewaters with high suspended sohds concentration. Separation and Purification Technology, 79, 20—25. 

See the book by E.E. Michaelides, Particles, Bubbles Drops (World Scientific, 2006) and the paper by J. Fabre and A. Line, Modeling of two-phase slug flow Annual Rev. Fluid Meek, 24,21M6,1992). 

Barnea, D., and N. Brauner, 1985, Holdup of the Liquid Slug in Two-Phase Intermittent Flow, Int. J. Multiphase Flaw 77 43-49. (3)... 

In annular flow, the lighter of the two phases (water) flows in the centre of the channel (core flow), while the heavier one (ionic liquid) is contained in a thin film wetting the channel wall. Annular flow occurs at high velocities of the water phase, where the inertia of the water is sufficiently high to break through the ionic liquid in slug flow. Depending on mixture velocity and ionic liquid volume fraction different kinds of annular flow, namely quasi, throat and rivulet, were observed (Fig. 4.2). 

When two immiscible phases come into contact at a junction, an approximately parabolic flow profile can be obtained for a two-phase stratified flow in a common pressure-driven microfluidic system. On the other hand, in a droplet-based flow, stimulated by the shear between the stationary fluid at the channel wall and the slug axis, there exists internal recirculation in both continuous and dispersed phases [8]. Complex flow patterns may appear under different conditions, depending on the forces acting on the fluids. 

In two-phase pipe flows, the slip velocity or, equivalently, the drift flux is related to the void fraction. This leads to the occurrence of kinematic waves which convey void fraction signals. Kinematic waves have been investigated experimentally in air-water two-phase flows by inducing small void fraction disturbances at the inlet of vertical ducts, the average void fraction varying from 0.01 (bubbly flows) to 0.41 (slug flows). The temporal fluctuations of the void fraction are detected in regularly spaced cross sections by non intrusive impedance probes. The statistical... 

Figure 8 Conversion as a function of reactor diameter. Bubbling bed models Solid lines two-phase bubbling bed model (19) with a =0 short dashes same model with =0.005 long-short broken lines Orcutt model with mixed dense phase. Slug flow model Hovmand-Davidson (A5,46). For conditions see Table 3.

The two phase up-flow patterns in vertical hne are bubble, slug, forth (or chum), annular, mist, in the order of increase vapor flow. A generally accepted down-flow two phase flow regions are not available. 

The inlet section is designed to separate out most of the liquid phase such as large slugs or droplets in a two phase stream. These simple devices redirect the inlet flow... 

Slug flow must be avoided in all two-phase applications. The designer must be alert for two-phase flow developing in a system. In one case, absorber liquid going to a lower pressure stripper produced a two-phase mixture. The absorber stream entered the stripper in a line that was elled down onto the stripper tray. The two-phase mixture beat out a section of trays. A /4-in. protection plate was provided and this had a hole cut in it in two years. 

Equation 6-108 is also a good approximation for a fluidized bed reactor up to the minimum fluidizing condition. However, beyond this range, fluid dynamic factors are more complex than for the packed bed reactor. Among the parameters that influence the AP in a fluidized bed reactor are the different types of two-phase flow, smooth fluidization, slugging or channeling, the particle size distribution, and the... 

Whenever two-phase flow is encountered in facility piping it is usually in flowlines and interfield transfer lines. Some designers size liquid lines downstream of control valves as two-phase lines. The amount of gas involved in these lines is low and thus the lines are often sized as singlephase liquid lines. Oversizing two-phase lines can lead to increased slugging and thus as small a diameter as possible should be used consistent with pressure drop available and velocity constraints discussed in Volume 1. 

Haberstroh, R. E. and P. Griffith, The Slug-Annular Two-Phase Flow Regi ne Transition, Am. Soc. Mech. Engr., Paper 65-HT-52,... 

Fair s presentation provides the development of the design technique. The method recognizes two-phase flow in a vertical reboiler and points out that slug-type flow is most predominate and that mist-flow should be avoided. 

---