Study On Leakage Flow Characteristics Between Contact Mechanical Sealing Interfaces

The requirements of long-term safe operation,environmental protection and resource conservation makes the mechanical seal for preventing leakage of the device once again become the focus of attention of researchers.Compared with the non-contact mechanical seal,the contact mechanical seal not only has a simple structure without the need for complex end supply or gas supply blockage control system,with manufacturing economy,low maintenance costs and other advantages,but also has a good sealing performance in certain design conditions.However,the presence of asperities on sealing ring surface makes the contact unsatisfactory,the fluid may still leak through the sealing interfaces by the channel under the effect of pressure difference,causing the sealing failure,so it is extremely important to establish a suitable interface leakage microchannel model for mechanical seals and analyze the flow characteristics of the leaking fluid.The existing "fluid exchange flow theory" is difficult to explain the existence of leakage between the sealing surfaces in the static state,the "wave" theory and fractal leakage model also failed to solve the leakage problem between two parallel end faces when the run-induced "wave" disappeared.In this paper,we do researches on a leakage microchannel between the interfaces of a contact mechanical seal and the flow characteristics in the channel.The main research tasks and research results are as follows:(1)The contact model Ar=f(pc,An,D,G,l,E,?2)of asperities on two seal end faces was established.The contact between the end faces of the mechanical seal is simplified as a contact between a rigid smooth plane and an elastic rough plane,and the viewpoint of using the morphological parameters D,G and the opening size of the asperity l which is independent of the contact condition to describe the initial surface profile was proposed.Based on this,the contact model on the sealing end faces was established by combining the fractal theory and the contact mechanics theory.The influences of end face load,the profile parameters D,G of the rough surface and the material properties of the seal ring on the true contact area of the sealing interface were analyzed.Then,the reliability and rationality of the contact model of seal end faces were verified by comparing it with the results of existing models and experiments.(2)A leakage microchannel model on the sealing interfaces was established in this paper.The initial porosity of the contact interface of the rotating and stationary rings was solved by the established contact face model of mechanical seal.According to the principle of invariant volume of asperity before and after deformation,we discussed the influence of sealing end face load,surface profile parameters and material properties on the porosity of sealing porous interfaces.Based on the percolation theory,the percolation threshold of the sealing interfaces under different grid layers was analyzed and comparing the porosity of the sealing interface under the action of end face,the percolation state of the sealing interface is determined,that is,the single-layer grid percolation.According to this,a leakage microchannel model on the sealing interfaces consisting of variable cross-section holes was established.(3)The flow characteristics of the fluid in the leakage microchannel of the sealing interfaces were revealed.Based on the characteristics of the pore throat morphology of the leakage microchannel,the leakage microchannel structure composed of the hole sections was simplified.The expression of the resistance of the fluid flow in the leakage channel was deduced by the Fanning formula,and the flow resistance of the fluid in the microchannel between the entire sealing interfaces was obtained by Fluent simulation simultaneously.Then,based on the simplified leakage microchannel and pore throat dimensions,we used the continuity equation and the N-S equation to give the relationship between the leakage rate in the microchannel and the geometric parameters of the microchannel,the internal and external pressure difference of the sealed chamber,and characteristics of the sealed medium.(4)The effect of surface morphology and pressure difference on the leakage rate was verified by experiments.A simple mechanical seal static test device was designed and the leakage test was carried out on six groups of sealed chambers(composed of six soft rings with different surface topography and one hard ring).The influences of the surface morphology(D,G,Ra,Rz,Ry)and the pressure difference between the inner and outer pressures of the sealed chamber on the leakage rate were obtained by one-variable method.It was found that the experimental data has good agreement with the theoretical calculation value,and the rationality of the leakage channel model was verified.