Rotary lip seals serve as critical sealing components in industrial equipment, traditionally relying on the reverse pumping theory for their sealing mechanism. However, increasing operational demands characterized by high fluid pressure differentials, elevated speeds, and multi-physics coupling environments have revealed limitations in the applicability of the classical theory. This study aims to develop a comprehensive model to quantitatively characterize rotary lip seal performance, specifically frictional torque and reverse pumping rate, and to elucidate underlying mechanisms beyond classical theory. We developed a Mixed Thermo-Hydrodynamic Lubrication (MTHL) model that explicitly integrates fluid–solid–thermal coupling effects to simulate seal behavior under complex operating parameters. The simulations reveal that reverse pumping rate increases near-linearly with rotational speed from −8.54 mm3/s (0 m/s) to 122.82 mm3/s (3 m/s) and 220.27 mm3/s (6 m/s), validating classical theory, while under elevated fluid pressure differentials, a distinct non-monotonic trend emerges: rates evolve from 122.82 mm3/s (0.10 MPa) to 172.93 mm3/s (0.12 MPa), then decline to 52.67 mm3/s (0.18 MPa), and recover to 69.87 mm3/s (0.22 MPa), a phenomenon that cannot be explained by classical sealing mechanisms. Mechanistic analysis indicates that this anomaly stems from a competitive interaction between pressure-driven and shear-driven flow. This discovery not only enhances the reverse pumping theoretical system but also provides a theoretical foundation for optimizing sealing performance under diverse operational conditions.
He et al. (Mon,) studied this question.