INFLUENCE OF THE SURFACE VISCOSITY ON THE DRAG AND TORQUE COEFFICIENTS OF A SOLID PARTICLE IN A THIN LIQUID LAYER

The present paper provides a short literature survey of the treatment of particle motion in fluids as a basis of the author's own work in th is field. The work relates to the motion of a small solid particle ins ide a thin liquid film. The particle motion is treated numerically to provide information of interest to thin film liquid coating. The numer ical computations yield information on the local velocity and pressure distributions, but also integral information expressed in drag and to rque coefficients. The computations are carried out for stationary flo ws of low Reynolds and capillary numbers and results are presented for different values of surface dilatation and shear viscosities. Transla tional and rotational motions of the particle are considered by integr ating the resultant second-order partial differential equation with an alternating direct implicit method. The numerical results reveal in a ll cases the strong influence of the surface viscosity on the motion o f the solid particle in the viscous liquid layer when the radius of th e particle is of the same order of magnitude as the thickness of the l iquid film or when the particle is close to the liquid-gas interface.