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A 3D thermo-elasto-hydrodynamic (TEHD) model is presented to study the effects of triangular dimples on the loadcarrying capacity, leakage and friction of a mechanical seal operated under mixed or full film lubrication conditions. The model is solved by the finite element method (FEM), which takes into account the effects of the Jakobsson-Floberg-Olsson (JFO) cavitation boundary condition, surface roughness, elastic-plastic contact, thermo-elastic deformation, and the temperature-viscosity relation. The numerical results of the TEHD model are quite different from those of the hydrodynamic (HD) and thermo-hydrodynamic (THD) models, especially at high speeds. In order to obtain the optimum shape and distribution of the triangular dimples, a comparative study is conducted to investigate different distributions of equilateral triangles and isosceles right triangles. The results show that a surface textured mechanical seal with isosceles right triangular dimples has the most significant hydrodynamic and pumping effects which, in turn, are beneficial to sealing face opening behavior and leakage limitation. The theoretical results are in good agreement with the experimental ones, and offer new guidance for the future design and development of high-speed mechanical seals for aviation piston pumps.

Spiral groove dry gas seal (S-DGS), the most widely used DGS in the world, encounters the problem of high leakage rate and inferior film stability when used in high-speed machinery equipment, which could not be well solved by optimization of geometrical parameters and molded line of spiral groove. A new type of bionic cluster spiral groove DGS (CS-DGS) is proved to have superior film stability than S-DGS at the condition of high-speed and low-pressure numerically. A bionic CS-DGS is experimentally investigated and compared with common S-DGS in order to provide evidence for theoretical study. The film thickness and leakage rate of both bionic spiral groove and common spiral groove DGS are measured and compared with each other and with theoretical values under different closing force at the condition of static pressure, high-speed and low-pressure, and the film stiffness and stiffness-leakage ratio of these two face seals are derived by the relationship between closing force and film thickness at the steady state. Experimental results agree well with the theory that the leakage and stiffness of bionic CS-DGS are superior to that of common S-DGS under the condition of high-speed and low-pressure, with the decreasing amplitude of 20% to 40% and the growth amplitude of 20%, respectively. The opening performance and stiffness characteristics of bionic CS-DGS are inferior to that of common S-DGS when rotation speed equals to 0 r/min. The proposed research provides a new method to measure the axis film stiffness of DGS, and validates the superior performance of bionic CS-DGS at the condition of high-speed and low-pressure experimentally.

The supercritical carbon dioxide (SCO2) Brayton cycle system is an energy conversion system with great potential, and its efficiency can be improved significantly by using low-leakage dry gas seals in SCO2compressors and gas turbines. However, the high-pressure and high-speed conditions of a SCO2dry gas seal make the impact of turbulence not negligible. In this paper, the influences of flow state on flow field distribution and sealing performance of a SCO2dry gas seal are studied, the criteria for determining the overall flow state into the sealing gap are proposed. Explicit expressions of the flow factor for flow state determination are obtained based on the artificial neural network algorithm. The results show that turbulent flow is easy to occur in a SCO2dry gas seal, leading to a remarkable error in predicting sealing performance using a laminar flow model. When employing a laminar flow model, there is a large error on opening force in the transition regions between turbulent and transitional flows, and a large error on leakage rate at high inlet pressure and close to the critical temperature compared to those obtained by using a turbulent flow model. In addition, the flow state judgment method proposed in this paper can accurately determine the overall flow state of a SCO2dry gas seal under different operating conditions.