A spherical particle straddling a fluid/gas interface in an axisymmetric straining flow

Numerical solutions, obtained via the boundary-integral technique, are used to consider the effect of a linear axisymmetric straining flow on the existence of steady-state configurations in which a neutrally buoyant spherical particle straddles a gas–liquid interface. The problem is directly applicable to predictions of the stability of particle capture in flotation processes, and is also of interest in the context of contact angle and surface tension measurements. A primary goal of the present study is a determination of the critical capillary number, Ca_c, beyond which an initially captured particle is pulled from the interface by the flow, and the dependence of Ca_c on the equilibrium contact angle θ_c. We also present equilibrium configurations for a wide range of contact angles and subcritical capillary numbers