Particle on the Interface Between Two Fluids

The motion of a particle across the interface between two fluid phases is an important part of the processes of separation and purification of one of the phases from suspended particles. In this case, in addition to the interfacial excess energy, pure hydrodynamic effects of drag against the phase transition play an important role. 

The motion of a disk whose plane coincides with the interface between two fluids with viscosities m and fi2 was studied in [387]. The drag forces in the Stokes motion of this disk with velocity U along the tangent and the normal to the interface are given by 

In the special case n = fj,2, formula (2.9.15) implies (2.6.16) (up to different notation of indices) for a disk moving in a homogeneous medium. 

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