Bubble Size and Interfacial Area

As said earlier, the interfacial area per unit volume is an important component of the volumetric mass transfer coefficient. In fact, it is the part of kLa that is most susceptible to changes in operation variables and fluid properties. The mass transfer coefficient kL varies only within a limited range (147), but the interfacial area is the main component responsible for the changes in mass transfer rate due to variations in turbulence, initial bubble size, and liquid properties.

The methods for measurement of the interfacial area are based either on rapid chemical reactions or on direct measurement of bubble size. If a mean bubble size can be defined, then the interfacial area can be evaluated with the aid of the holdup measurement, since, in a population of homogeneous bubble size, it can be applied:

where the Sauter mean diameter (dS) is given by d = S

and n is the number of bubbles of diameter d

There are very few published data on bubble size applicable to ALRs. For the riser, the correlation presented by Miyahara et al. (57) for the volumetric mean diameter

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