Investigation on the influencing mechanism and quantitative evaluation of stirred heat effect in high-speed mechanical seals

Abstract

Stirred heat is much severe in mechanical seals under high-speed conditions, which significantly affects seal's heat transfer and dissipation characteristics. A three-dimensional thermohydrodynamic numerical model consisting of the fluid film, sealed chamber and sealing rings is developed to investigate the influencing mechanism of stirred heat by the comparative analyses of fluid flow, heat generation and transfer and evaluates its influence level by the parameterized analyses about the rotational speed, flushing flow rate, sealing pressure and sealing face structure. Firstly, in terms of cooling flow, the cold fluid flow from sealed chamber into sealing gap is impeded by the high-speed shear effect of rotor outer sidewall, and a larger vortex namely a flow dead zone is generated at the spiral groove root due to the turbulent flow regime, which significantly impede the cooling level of fluid film and sealing end faces. Secondly, in terms of heat generation, because of the high-speed shear effect of rotor, a much larger effective viscosity, radial velocity gradient, turbulence intensity and turbulence dissipation rate are generated by the turbulent flow in sealed chamber, which are responsible for the significant stirred heat. Finally, in terms of heat transfer, the temperature difference between the sealing rings and sealing chamber fluid is narrowed by the stirred heat, suppressing the convective heat transfer level. The above phenomena lead to an increase in the overall and sealing face temperature rises, and a deterioration of the sealing performance. The rotational speed has the most significant impact on the stirred heat. At the most severe, temperature rise of stirred heat for seal is up to 34 %, the decrease of load-carrying capacity is up to 17 %. Increasing flushing flow rate has a positive effect on the dissipation of stirred heat. The sealing face structure hardly affects the stirred heat generation and transfer.