Coupling Model and Performance Analysis of Partial Porous T-Grooved Mechanical Seal

Low viscosity liquid (such as liquid hydrogen, liquid oxygen, liquid methane, etc) as the sealing medium of the mechanical seal has difficult film formation and heavy wear problems. Numerous studies have shown that the application of various modifications such as micro-channels, compartments, micro-pores, texturing in mechanical non-contacting seals causes changes of hydrodynamic of the medium layer. To increase the film formation rate of dynamic pressure seals and reduce end face friction, apartial porous T-grooved mechanical seal (PPT-MS) is proposed by introducing porous materials into T-grooved mechanical face seals. Due to the existence of porous material, PPT mechanical seal in the working process both the sealing medium flow in the sealing gap, but also the sealing medium seepage in the porous material. The seepage characteristics of the sealing medium within the porous mass have an important influence on the lubrication performance of the liquid film. For exploring the influence of seepage and film pressure on the liquid film lubrication performance of mechanical seal, a mathematical model of PPT-MS is developed by considering the coupling effect between the fluid seepage mechanics of porous matrix and the hydrodynamic lubrication mechanics of fluid film. Taking the cavitation of fluid film into consideration, the seepage equation and the Reynolds equation are solved by using finite element method. The calculated results of this method are in good agreement with the numerical results and experimental data in the literature, which proves the feasibility of this method. The pressure distribution and the density ratio distribution of the PPT-MS, conventional T-Groove mechanical seal(T-MS) and porous T-Groove mechanical seal (PT-MS) were compared. The effect of permeability and geometrical parameters of porous matrix on sealing performance are investigated and the sealing mechanism of the PPT-MS was revealed. In addition, the opening force of film was investigated simply for different T-groove geometric parameters such as the groove depth, the groove-dam ratio α₁, the width ratio of drainage groove α₂, the groove length ratio β₁ and the length ratio of drainage groove β₂. With the opening force as the target, the structural parameters of T-groove α₁=0.2, β₁=0.2, α₂=0.8, β₂=0.8 can be preliminarily obtained. The results showed that in the upwind side of T-Groove would produce a low-pressure area and in the windward side of T-Groove would produce a high-pressure area. The fluid was introduced into the sealing gap through the porous matrix under the effect of cavitation suction effect when the porous was placed in the low-pressure zone of the T-Groove, improving the load-carrying capacity of the fluid film and enhancing the lubrication. The opening force increased and the friction coefficient decreased with the increasing permeability of porous matrix, at the same time, there was some increase in leakage rate and the permeability of 1×10⁻¹⁴ ~5×10⁻¹⁴ m² was more appropriate under comprehensive consideration of sealing performance. When the circumferential width of the porous accounts for half of the width of the circumferential groove area of the T-Groove, the opening force was maximized. When the porous gradually spread to the high-pressure area of the T-Groove in the circumferential direction, the sealing medium started to penetrate into the porous from the sealing gap, which would inhibit the hydrodynamic effect of the liquid film to a certain extent. The present results could guide the design of porous mechanical face seals.