g 100

n 20 ass 0

^ 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 Superficial gas velocity (m/s)

Figure 33. Mass transfer coefficient kLa as a function of gas superficial velocity for external-loop ALRs. Correlations are presented in Table 7.

For Newtonian liquids, this equation reduces to:

Kawase and Moo-Young (140) compared their model with data and correlations published by various investigators and found satisfactory agreement for both Newtonian and non-Newtonian liquids.

For ALRs (64), the flow in the reactor may be similar to that in bubble columns if the internal recirculation is high, or it may be even closer to net two-phase flow in pipes, in which case the equations for heat transfer in pipes can be used (126).

Blakebrough et al. (158) studied heat transfer rates in an external-loop airlift fermentor used for culturing Asper-gillus niger. They concluded that the enhancement of the heat transfer rate could be explained by disturbances in the liquid layer near the surface caused by the presence of the microorganisms.

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