The Study Of Sealing Liquid With Magnetic Fluid

Magnetic fluid seal is a new type of seal method,which has the advantages of zero leakage,long life and high reliability,so it is widely used in the fields of aeronautics,space,military industry,etc.However,the existing magnetic fluid seals are limited to vacuum seals and low-pressure gas seals,and the solution to the liquid seal is unsolved.The seal involved in shipping,deep-sea,petrochemical and other industries is mostly liquid seal.With the development of these industries,the traditional seal forms has been unable to meet its growing seal requirements.The advantages of zero leakage and high reliability of magnetic fluid seal in gas and vacuum seal have attracted domestic and overseas scholars to study the problem of sealing liquid with magnetic fluid.In order to solve the problem of sealing liquid medium by magnetic fluid,this paper explores the transfer mechanism of liquid loading in multistage magnetic fluid seal,reveals the failure mechanism of sealing liquid by magnetic fluid,and invents a new structure of magnetic fluid seal used to seal liquid medium,which realizes online performance detection of magnetic fluid seal and significantly improves its seal life.The main work of this paper is as follows:(1)The pressure transfer mechanism of sealing liquid medium by magnetic fluid is explored.In the aspect of theory:based on the motion equation of magnetic fluid,Bernoulli equation and boundary conditions of magnetic fluid for sealing liquid medium are discussed,and then the pressure capacity formula of magnetic fluid sealing liquid medium is derived,and the relationship between the pressure capacity of magnetic fluid seal and the volume of magnetic fluid is derived.According to the pressure transfer process of magnetic fluid seal,the mathematical models of magnetic fluid seal for gas seal and liquid seal are established respectively,and the influencing mechanism of pressure between seal stages during pressure transfer is revealed.In the aspect of experiment,the experimental set-up to study the pressure transfer process of magnetic fluid seal was designed and constructed.The transfer mechanism of the pressure load of the sealed liquid medium in rmultistage magnetic fluid seal and the flow phenomenon of the magnetic fluid between adjacent seal levels were studied experimentally.The pressure loading process of the liquid medium is a step-by-step transfer.In the process of pressure loading,the leakage and self-repair of magnetic fluid at the upstream seal stages play a very important role.During the loading process of the liquid medium,the magnetic fluid reveals a superior performance of self-repair than of the gas medium.When the sealed liquid medium fills the seal stage,the pressure difference on both sides of the seal stage always remains constant during subsequent transmission,and is equal to the seal pressure capacity of the seal stage.The assembly process of the magnetic fluid seal and the loading process will cause the magnetic fluid to flow between the adjacent seal stages,resulting in the uneven distribution of the magnetic fluid between the seal stages,which weakens the total pressure capacity of sealing liquid medium by magnetic fluid.(2)The failure mechanism of sealing liquid medium with magnetic fluid was studied.In the aspect of theory,the factors and mechanism of the instability of the contact interface between the magnetic fluid and the sealed liquid medium are discussed.The effects of magnetic field,rotating speed,pressure and other factors on the stability of the contact interface between the magnetic fluid and the sealed liquid medium were calculated by FLUENT software.In the aspect of experiment,the interface state observation set-up of sealing liquid medium by magnetic fluid was designed and built.The effects of rotating speed,magnetic field,pressure and volume of magnetic fluid on the sealing life of magnetic fluid were studied.In the process of sealing the liquid medium,the sealed liquid medium will "flush" and "infiltrate" the magnetic fluid.These two functions are throughout the whole life of the magnetic fluid seal when sealing liquid medium.At the beginning of the seal,due to the first-order buoyancy principle of the magnetic fluid,the "infiltration" function of water to the magnetic fluid will be inhibited and the effect is weak.The higher the rotating speed,the stronger the effect,the faster the magnetic fluid loss,and the shorter the sealing life of magnetic fluid.In the later period of the seal,as the magnetic fluid was "rinsed" less and less,and as the accumulated effect of the previous "infiltration" effect resulted in the decline of the magnetic fluid's performance,the "infiltration" effect of water was significantly enhanced.Then,magnetic fluid seal failure,sealed liquid medium leakage.The experimental results show that the volume of magnetic fluid that can be accommodated under the single-stage pole teeth is an important factor influencing the sealing life of magnetic fluid.(3)According to the pressure transfer mechanism of sealing liquid with magnetic fluid and the failure mechanism of sealing liquid with magnetic fluid,a new structure suitable for sealing liquid medium by magnetic fluid is developed.The new seal structure can realize online monitoring of the seal performance of magnetic fluid seal for liquid sealing and give warning signal before seal failure.After receiving the warning signal,the magnetic fluid can be supplied to the seal gap automatically,which greatly improves the life of the magnetic fluid seal.The research results of this paper are of great significance to solve the problem of magnetic fluid seal for sesaling liquid medium.It is expected to be applied to the sealing involved in petroleum,chemical industry,ship,deep sea and other industries,bringing direct economic benefits while saving resources and protecting the environment.It has great economic and social benefits.