Phase cocurrent

An outstanding feature of two-phase cocurrent flow is the variety of possible flow patterns, ranging all the way from a small quantity of gas dispersed as bubbles in a continuous liquid medium, to the opposite extreme of a small amount of liquid dispersed as droplets in a continuous gas stream. The importance of these flow patterns can be shown when one plots the rate of a transport process as a function of a flow rate of one phase while the flow rate of the second phase is maintained constant. The flux will be found not merely to increase or decrease in a smooth fashion, but rather to show in different flow ranges minima or maxima demonstrating the presence of fundamentally different transfer processes. A comprehensive understanding of the flow processes is necessary before the nature of the flow pattern can be predicted for any given set of flow conditions. 

In the years since 1940, a voluminous literature has appeared on the subject of two-phase cocurrent gas-liquid flow. Most of the work reported has been done in restricted ranges of gas or liquid flow rates, fluid properties, and pipe diameter, and has usually been specific to horizontal or vertical pipe lines. The studies have in most instances been isothermal when two components were being considered nonisothermal cases were almost entirely single-component two-phase situations. Reports of investigations of two-phase two-component cocurrent flow where one component is being transferred across the interphase boundary are nearly nonexistent. 

Ward and DallaValle (W2) studied the two-phase cocurrent flow of air and four non-Newtonian fluids in three horizontal pipes (I.D. 0.82 to 1.60 in.). Flow rates were such that both phases were in turbulent motion. The flow-behavior index of the liquids used was varied from 0.31 to 1.00,... 

V. Specchia and G. Baldi, Pressure drop and liquid hold-up for two-phase cocurrent flow in packed beds, Chem. Engng. Science, 32 (1977) 515-523. 

Nonagitated three-phase cocurrent-upflow fluidized-bed reactors... 

Nishikawa et al.92 measured /cr. i. in a three-phase cocurrent gas-liquid-flow spouted-bed column. Absorption rates of oxygen into copper-catalyzed sodium sulfite solution were measured. The data indicated that the k,a, increased with both gas and liquid flow rates. As shown by Ostergaard and Fosbol,103 while kLaL increased with particle size, its values in the case of 1.01-mm particles were lower than the ones in the absence of solids and otherwise identical conditions. The effect of particle size on kLaL obtained by these investigations is shown in... 

Grosser, K. Carbonell, R.G. Sundaresan, S. Onset of pulsing in two-phase cocurrent downflow through a packed bed. Am. Inst. Chem. Eng. J. 1988, 34, 1850. 

There is relatively little information on the pressure drop in two-phase cocurrent downflow packed beds. Larkins et al. [21] have proposed the following correlation for the two-phase frictional pressure drop ... 

For two-phase cocurrent gas-liquid flow, there is the wide variety of possible flow patterns which are governed principally by the physical properties (density, surface tension, viscosity of gas, rheology of liquid), input fluxes of the two phases and the size and the orientation of the pipe. Since the mechanisms responsible for holdup and momentum transfer (or frictional pressure drop) vary from one flow pattern to another, it is essential to have a method of predicting the conditions under which each flow pattern may occm. Before developing suitable methods for the prediction of flow pattern, it is important briefly to define the flow patterns generally encountered in gas-liquid flows. Horizontal and vertical flows will be discussed separately as there are inherent differences in the two cases. 

Szeri.A., Shah.Y.T. and Maagavkar,A. "Axial dispersion in two phase cocurrent flow with fast and instantaneous reactions". Chem.Engng.Sci. 31 (1976) 225. 

Iliuta I, Thyrion FC. Gas-liquid mass transfer in fixed beds with two-phase cocurrent downflow gas/Newtonian and non-Newtonian liquid systems. Chem. Eng. Technol. 1997 20 538. 

Chou TS, Worley EL, Luss D. Local particle-liquid mass transfer fluctuations in mixed phase cocurrent downflow through a fixed bed in the pulsing regime. Ind. Eng. Chem. Fundam. 1979 18 279. 

Three phase packed bed reactors, filled with catalyst pellets with a size of a few mm. They are usually operated in one of the following ways with the liquid as a continuous phase (cocurrent upflow) or with the liquid running downward in a thin film (triclde flow, cocurrent downward). At high flow rates, pulsating two-phase flow can be obtained. Countercurrent flow is rarely used. 

Chou, T. S., F. L. Worley and D. Luss. Local Particle-Liquid Mass Transfer Fluctuations in Mixed-Phase Cocurrent Downflow Through a Fixed Bed in the Pulsing Regime. Ind. Eng. Chem. (Fundan) 18 (1979) 279-283. 

Hochman, J. M. and E. Effron. Two-Phase Cocurrent Downflow in Packed Beds., Ind. Eng. Chem. Fundam. 8 (1969) 63-71. Hoftyzer, P. J. Trans. Inst. Chem. Engrs. (London) 42 (1964) T109-T117. 

Kan, K.M. and PoF. Greenfield, "Pressure Drop and Holdup in Two-Phase Cocurrent Trickle Flows through Beds of Small Particles", I/EC ProCo Des, Dev, 18, (1979) 740-744,... 

Suppose the two-phase cocurrent flow is not at steady state. Instead, one of the phases is introduced as a pulse or in an interrupted fashion so that we have pulses of the second phase moving in the positive z-direction as the first phase moves continuously. If this... 

The model we develop in this appendix is thus based on a two-phase, cocurrent flow force balance that relates the cross-sectional liquid void fraction... 

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