Mass Transport of a Two Phase Flow Through a Converging Gap With One Moving Wall

ABSTRACT Mechanical seals are designed to separate two fluid phases from each other, exemplified by the separation of ambient air and hydraulic oil in hydraulic cylinder applications. These seals necessarily include a converging gap, even at a microscopic level. During operation, a rod in contact with both phases moves through this converging gap. Practically, during a rod instroke motion, a thin film of oil sticks to the rod's surface. A simulation model of this process focuses on a laminar two‐phase flow through the converging gap and one moving wall with no‐slip boundary conditions. The simulation considers a phase distribution model and parameters such as surface tension, the contact angle for rigid body contact, and interface thickness. The numerical solution indicates the existence of two types of solutions, dependent on the initial thickness of the fluid film. The first type involves the suction of ambient air through the converging gap, while in the second, the fluid is wiped off the rod. For a rigid seal, a sharp snapping point separates these two solution types. Contrary to intuition, it is found that a parameter set exists, where a thinner oil film leads to a higher oil mass flow, while a thicker oil film results in reduced oil transport. This “blocking” effect can be understood by the influence of outer boundary conditions, the viscosity parameters of the two phases, and the related velocity field.