Marangoni effect mass, transfer coefficient

While interfacial contaminants tend to reduce the mass transfer coefficients by causing the droplets to be stagnant rather than circulating, another surface effect may enhance mass transfer. This is the Marangoni effect, whereby local variations in interfacial tension due to the mass transfer process itself can create rapid motions (interfacial turbulence) at the interface. 

Marangoni convections are very important to the operation of extractors. On the one hand they can increase the mass transfer coefficients on the other hand they can reduce the interfacial area. Which mechanism has the larger effect cannot be decided generally, it depends on the system and equipment at hand. 

Marangoni effect is a general terra for surface flow phenomena resulting from the appearance in the interface of an interfacial tension gradient. These phenomena produce traction on the adjoining sublayers and lead to two distinct and separate effects the flux-intensive surface renewal phenomena and the area-intensive thin-film phenomena. The first phenomena predominate when the depth of the liquid is much larger than the depth of penetration of surface movement and the second are important when the two depths are comparable. In the first case the affected process parameter is the mass transfer coefficient and in the second case the interfacial area. 

Zhou CF (2005) Study on the influence of Marangoni effect and other factor on the mass transfer coefficients. M.S. dissertation, Tianjin University, Tianjin, China (in Chinese)... 

In the study of mass transfer, the fluid element (microcell) can be used to describe the behaviors of the process. Under the condition of no Marangoni effect, according to the penetration theory, the fluid element flows randomly from fluid phase to the interface and stays there within residence time T for unsteady mass transfer and then go back to the bulk fluid. The liquid-phase mass transfer coefficient is given by the following ... 

An important effect ( ch is not taken into account in the equation presented in Chapter 3 for calculation of liquid side mass transfer coefficient, is die effect of the interfacial tnihulence (effect of Marangoni). Because diis e could exist for all types of packings, it is (xmsidered in the present chapter apart fiom the packing construction. 

The following simple algorithm for calculation of the influence of the Marangoni effect on the mass transfer coefficient is xt sed [16] ... 

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