How is Marangoni shear stress calculated in FLUENT
 

FLUENT use CSF model to calculate the effect of surface tension. In its help film, it is only said that "The solver will include the additional tangential stress terms (causing what is termed as Marangoni convection) that arise due to the variation in surface tension coefficient." No other detail is provided.

How is Marangoni shear stress calculated in FLUENT? What formula is used?