Study On Dry Gas Seal Performance Of Spiral Groove Considering Actual Gas Effect

Dry gas seal, another called an end face gas lubricated mechanical seal, is an advanced non-contacting mechanical seal technology. The theory of modern dry gas seal was from gas dynamic pressure bearing theory. At the beginning, the dry gas seal was used to centrifugal compressors in offshore gas transport equipment. Then it was extended to the end face seal of shaft in high speed rotating machines such as centrifugal pumps, fans, compressors, expanders and turbines. Dry gas seal has some advantages of high temperature resistance, corrosion resistance, high efficiency, long life, low wear, low leakage rage, etc. The applications gradually were expanded to low speed operating equipment like the reactor. Scholars at home and abroad have turned to research low speed conditions of dry gas seal. During their studies, much of the gas was taken as an ideal gas. As the pressure was increased, the real gas deviates from the ideal gas took place. The real gas effect should be taken into consideration in research on low speed dry gas seals.Spiral groove dry gas seal was the object of study in this paper. In order to analyze the effect of the real gas and the slip flow on performances of the low speed dry seals, the effective viscosity coefficients instead of the dynamic viscosity of the gas was taken, and taking the Virial state equation of the real gas instead of the state equation for ideal gas was used to modify the pressure controlled equation of the narrow groove theory of the spiral groove dry gas. Air, N2, H2, CO2 were taken as the examples, the leakage rate, the pressure of groove root, the opening force of the spiral groove dry gas seals were calculated. The leakage rate, the pressure of groove root and the opening force of the dry gas seals as the model respectively being ideal gas without slip flow condition, ideal gas with slip flow condition, real gas without slip flow condition and real gas with slip flow condition was were calculated and compared. Taking air as the sealing gas and choosing a classic example, the influence of geometric and environmental parameters to spiral groove dry gas under low speed considering real gas effect was analyzed.The results showed that, the effect of slip flow the leakage rate increase, and let the pressure of groove root and the opening force decrease. The effect of real gas made the leakage rate, the pressure of groove root and opening force of susceptible compressed gas (Z<1), such as N2、H2、 CO2, increase and let the leakage rate, the pressure of groove root and opening force of non-susceptible compressed gas (Z> 1), H2, decrease. With the increase of pressure, the slip flow effect was decrease and the real gas effect was increased. With the increase of the pressure, the slip flow effect was decreased, the real gas effect increased. The effect of slip flow played an important role under low pressure, and the effect of real gas played an important role under high pressure. In order to calculate the performances of dry gas seal under low speed accurately, both of slip flow effect and real gas effect should be taken into consideration. The geometric parameters and environmental parameters had great influence on the performances of spiral groove dry gas seal. When the spiral angle was around 26°, the spiral groove was around 3.5μm, the land-to-groove ratio was 0.6-0.7, (ro-rg)/(ro-ri=0.6-0.7, the spiral groove dry gas seal could get the largest opening force. With the increase of the film thickness, the opening force decrease and the leakage rate was increased. Both the opening force and the leakage rate linear were increased, when the rotating speed was increased.