Study On Thermo-Hydrodynamic Effect In Mechanical Seals

Mechanical seals are widely used as shaft sealing on pumps, compressors and agitators. The contact mechanical seals cannot meet the requirement of long-term continuous operation because of the hard abrasion of the end faces. It is necessary to develop the fluid lubricated non-contact mechanical seals. The Thermo- hydrodynamic (THD) effect in non-contact mechanical seals includes the thermal wedge caused by the frictional heat of the fluid film and the hydrodynamic wedge of the shallow grooves fabricated on the end face of the rotating sealing ring. The study on the THD was carried out to investigate the effect of the frictional heat and thermal deformation of the end faces on the characteristics of the fluid film, to probe into the sealing mechanism of the non-contact mechanical seals and to discuss the application of THD in mechanical seals.The governing equation for the fluid flow in the gap between the two flat end faces of the sealing rings was derived from the momentum conservation equation and the mass conservation equation. For both the flat end face mechanical seal and the spiral groove mechanical seal, the pressure distribution equations of the fluid film in the undeformed gap and deformed gap were all derived. The equations for calculating the bearing force, the leakage rate and the frictional torque of the fluid film were also derived. For the spiral groove mechanical seal, the two-dimensional pressure distribution regularity was obtained by solving Reynolds equation using finite element method. The research results about the characteristics of the fluid film in the flat end faces indicate that the analytic solution is applicable for investigating the characteristics of the fluid film in the flat end faces. For the spiral groove mechanical seal, the analytic solution is more efficient but less accurate than the numerical method. The geometric parameters of the fluid film, the viscosity and the pressure of the sealed medium obviously affect the sealing performance of the flat end face mechanical seal. The geometric parameters of the spiral groove, such as the spiral angle, the depth, the width and the length, have an influence on the characteristics of the fluid film in the spiral groove mechanical seal. The bearing force of the fluid film in spiral groove mechanical seal is much larger than that in flat end face mechanical seal because of the hydrodynamic effect of the spiral grooves. For the flat end face mechanical seal, the bearing force of the fluid film in parallel gap is less than that in convergent gap but larger than that in divergent gap, and the leakage rate in parallel...