| The increase in operating speed and pressure in fluid machinery led to the improved design of the dry gas seal with high parameters so as to avoid wear caused by seal face mechanical deformation. In this paper, the characteristic of gas film, mechanism of pressure deformation and the influence of main causes on sealing performance were studied in both theoretical and experimental ways. The main conclusions are as follows:First, considering the effects of both microscale and thermal viscosity, the theoretical analysis model for mechanical seal was presented based on the theories of gas lubrication. The paper investigates the thermal viscosity effect, influence of surface roughness and gas sliding flow effect on the distribution of gas film pressure and sealing performance. It was found that the gas real-process could be as isothermal when in high pressure. The sealing dynamic pressure was increased, while leakage decreased due to the surface roughness and thermal viscosity effect. On the contrary, the gas sliding flow effect increased the leakage and reduced the loading capacity of gas film. The thermal viscosity effect dominated in affecting sealing performance.Than, the dimensionless mathematical model for torsion deformation and the fluid-solid coupling analysis model of the dry gas seals at high pressure were established based on the circle theory and equations of elasticity, the calculating method for the torsion deformation caused by the film pressure was present.The results showed that the leakage, stability and dynamic pressure effect increasd due to the film pressure compression deformation. The opening force was less affected by the film pressure compression deformation, and the leakage and stability had large influence relatively when the pressure po≥3MPa. The sealing performance would not be affected by compression deformation when the film thickness ho≥>3μm. The optimized values of spiral groove were obtained, they are as follows:spiral groove number Ng=12, groove depth ratio H2=3, spiral Angle a=15°, dam-groove ratio Ψ=0.7, the wide than the delta of spiral groove e=1.0.The torsion deformation cause the divergent clearance of high pressure gas seal faces, the step on the complex seal sections could be directly ignored when the step sizes of length or width are smaller than three millimeter.The torsion angle increased with the increasing step to outer radius ratio, step length ratio, length ratio of the position of secondary seal ring. The torsion angle decreased with the increasing of width ratio of step and inside radius. The influence of the width ratio of step on deformation had the most influence. The influence of position of secondary sealing ring on torsion deformation had little influence compared with the influence of structure parameters.The integrated pressure deformation made the seal clearance forming divergent clearance, and the torsion deformation dominated in the integrated deformation, the structure became the determinant in designing the dry gas seals at high pressure. The leakage was increasd and the opening force was weakened because of the integrated pressure deformation, the influence of the rotationl speed on film pressure and deformation had been small at high pressure. The influence of position of secondary O-ring seal on integrated deformation had little influence compared with the influence of structure sizes. The deformation of seal ring (structure b) which the bearing capacity per area was high was bigger than the seal ring (structure a) which the bearing capacity per area was small. The opening force of the seal ring of structure a was higher than structure b. Further, when the position of secondary O-ring seal was away from seal face, the position of secondary O-ring seal had large effects on deformation, the end face had difficult open, and the leakage was big. When the position of secondary O-ring seal was close to the seal face, the influence of the position of secondary O-ring seal on deformation had been small, it was comparatively easy to open, and the leakage was less. The influence of position of secondary O-ring seal on integrated deformation had little influence compared with the influence of structure sizes.Finally, the test device of high pressure dry gas seal was designed and built. The pressure deformation mechanism of high pressure dry gas seal were explained based on face wear and sealing performance by measuring the film thickness, leakage, face wear and so on. The experiment results showed the theoretical calculation was credible.When static pressure was higher than5MPa, the film thickness of every model was between4.0μm and6.1μm, the pressure can provide enough opening force to separate the seal faces. The struction factors had major impact on the opening force. Compared with the effect of size, the influence of the position of secondary O-ring seal on deformation and sealing performance was less. The face wear happened at the high pressure side of seal faces, the influence of structure on the lengh of wear track, wearing capacity, surface roughness and leakage which were all satisfied the theoretical prediction. The relation between the pressure deformation and wear was validation on the basis of data measured of wear and the theoretical calculation model was credible.The results obtained in the research perfect the high pressure deformation theory of dry gas seal systematically, and provide a reference for the deformation resistance of high pressure dry gas seal design and its application. |
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