The linear stability of the gravity-driven flow of a film in an annular space in the presence of a gaseous countercurrent

An analysis is performed of the hydrodynamic stability of the interface between a flowing gas and a thin film in a cylindrical geometry. A small perturbation method is employed to derive coupled systems of partial differential equations for each phase. Account is taken of the effects of the curvature of the cylinders, the Reynolds number, and the gas flow velocity (pressure gradient). It is shown that the gas flow, at low velocities, tends to stabilize the thin film, provided that no flow separation of liquid particles occurs at the interface.