B

Jg J

Zuber-Findlay's drift flux model allows us to derive the following equation, which establishes a connection between the gas holdup and b.

where C0 is the distribution parameter, J is the superficial velocity, Ubro is the terminal gas velocity, b is the flowing volumetric concentration, and u is the gas holdup.

Figure 8 gives a representation of the u ~ b plane. The 45° line indicates that u = b, an equality that is true only for nonslip flow, where the velocity of the gas is equal to the velocity of the liquid. Such a situation can be visualized for the case of very small bubbles in a relatively fast liquid. In this case, there is no influence of one phase on the motion of the other. As indicated in Figure 8, all the points below the 45° line indicate operation situations in which the liquid is driven by the gas:

This happens in the riser of ALRs. For all points above the line the opposite is true:

This latter condition reflects the operation of the down-

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