Void drift

Void drift that, as discussed previously, is apparently due to the strong tendency of the two-phase system to approach equilibrium conditions... 

Rhodes, and Scott Can. j. Chem. Eng., 47,445 53 [1969]) and Aka-gawa, Sakaguchi, and Ueda Bull JSME, 14, 564-571 [1971]). Correlations for flow patterns in downflow in vertical pipe are given by Oshinowo and Charles Can. ]. Chem. Eng., 52, 25-35 [1974]) and Barnea, Shoham, and Taitel Chem. Eng. Sci, 37, 741-744 [1982]). Use of drift flux theoiy for void fraction modeling in downflow is presented by Clark anci Flemmer Chem. Eng. Set., 39, 170-173 [1984]). Downward inclined two-phase flow data and modeling are given by Barnea, Shoham, and Taitel Chem. Eng. Set., 37, 735-740 [1982]). Data for downflow in helically coiled tubes are presented by Casper Chem. Ins. Tech., 42, 349-354 [1970]). 

Backfill surface, which is normally used to provide a gravity drain to the workings, but often also as access for personnel and materials (synonym drift, meaning (a)) Fractured waste rock deposited into a former opencast mine void (sedimentologically similar to spoil and to gottj)... 

Akagawa, Sakaguchi, and Ueda (Bull JSME, 14, 564-571 [1971]). Correlations for flow patterns in downflow in vertical pipe are given by Oshinowo and Charles (Can. J. Chem. Eng., 52,25-35 [1974]) and Barnea, Shoham, and Taitel (Chem. Eng. Sci., 37, 741—744 [1982]). Use of drift flux theory for void fraction modeling in downflow is... 

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... 

Kinematic waves result from the existence of a functional dependency between some "flux" and the corresponding "density", otherwise related through a balance equation (Whitham, 1974, p. 27). In two-phase flows, the foregoing flux and density are respectively the drift flux (volumetric flow rate of one phase with respect to the mixture) and the void fraction (volumetric concentration of the same phase in the mixture). Kinematic waves convey information on the flow structure and the associated variables such as the void fraction and the drift flux. In particular, they control flow pattern changes and density wave oscillations. 

The existence of two modes is confirmed by plotting (fig. 1) the data for the wave velocity and the drift flux as functions of the void fraction (the data is tabulated in Boure, 1988). According to the theory (Boure, 1988) the significant wave velocity is supposed to be the velocity C-W relative to the mixture center of volume with the definitions ... 

It is pointed out that, as shown by fig. 1, the domains of predominance of the two modes correspond to different relationships between the drift flux S and the void fraction a, i.e. to different flow regimes. It is suggested that mode 3 may result from individual interactions between otherwise independent bubbles, while mode 4 involves interactions between individual bubbles and swarms of bubbles (in active interactions themselves). 

Co is a distribution parameter correcting the basic one-dimensional model to allow for concentration and velocity profiles across the channel Mgj is a void weighted mean drift velocity... 

Following on with the continuum assumption, the control volume required for the material balance is shown in Figure 5.3a. The equilibrium concentration of jetsam within the control volume depends on the interaction of three components (i) convection (drift) caused by the bulk velocity, (ii) diffusion-like mixing, and (iii) segregation associated with movement through voids. The rate at which jetsam is spread over the cross section is mathematically depicted in Figure 5.3b. Of the three mechanisms shown, segregation is the only one that... 

Figure 15-50 Bubble formation in a fluid bed blender a) bubble consists of a wake, drift, and void space b) circulation of solids around the bubble.

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