Bubble Size and Specific Interfacial Area

Surface volume mean bubble size, d, and specific interfacial area, a, are linked via the local gas fraction, ( )  

measurements of any two will give the third. Direct photography, either through the walls (Machon et al., 1997) (which may not give representative samples) or with an optical probe (see Section 4-6.6.S) with image analysis is the most direct method, yielding local size distributions and gas fractions. 

Light transmittance methods for interfacial area have been widely employed in gas-liquid systems. Sridhar and Potter (1978) describe one of the more successful versions. The techniques are described in more detail in the liquid-liquid section. Chemical methods can be used to measure interfacial area, as described above (Section 4-7.5 Robinson and Wilke, 1974). Sampling methods are not suitable since it is impossible to withdraw a sample isokinetically. Generally, the results from chemical and physical methods do not agree. Chemical methods tend to have a bias toward the smaller bubbles of the distribution, whereas these may be missed by physical methods. 

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