Surface Tension and Additives

Surface tension is a liquid property that tends to counter bubble deformation and encourages bubble breakup (Akita and Yoshida, 1974 Mehmia et al 2005 Walter and Blanch, 1986). The result is a more stable bubble interface that leads to smaller bubble diameters, a more stable flow regime (Lau et al., 2004 Schafer et al., 2002), and higher gas holdups and interfacial areas (Kluytmans et al., 2001). It is also thought that a lower surface tension leads to a higher contact time because the liquid flow over the bubble surface is slowed (Lau et al., 2004). 

Surface tension is influenced by the presence of surfactants (Kantarci et al., 2005). Surfactants attach themselves to the bubble interface and form a hydrophilic boundary at the bubble surface. The result is a much smaller bubble size and a more rigid surface. This surface, in turn, lowers the bubble surface tension and further reduces the bubble rise velocity. 

Alcohols create smaller bubbles and higher gas holdups because they are either amphiphilic or have a lower surface tension so that the aqueous mixture supports smaller bubbles. This behavior has been observed for a large number of alcohols in an aqueous saccharose solution. The only exception was proved to be methanol. The theory, which was successfully tested by Zahradnik et al. (1999b), is that the longer carbon chains increase the effectiveness (of alcohols as coalescence suppressants) and cause methanol, the simplest alcohol, to lose its usefulness at a much lower concentration relative to the other alcohols (Zahradnik et al., 1999a Zahradnik et al., 1999b). 

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F. Different Kinds of Surface Tension and Additional Forms of the Laplace Equation... 

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