Study On Magnetic Fluid Seals Under High Speed Condition

The natrium-cooled fast reactor is the fourth generation nuclear power plant under research,in which the seal of the fast reactor main pump shaft is the key component to ensure the safety of the fast reactor.Magnetic fluid seal is a new type of dynamic seal,with advantages of zero leakage,high reliability and long life,which is suitable for the main pump shaft seal.The linear velocity of the shaft of the main pump can reach to 15m/s.Therefore,theoretical,simulation and experimental studies are carried out on the problems of high heating and centrifugal force existing in the magnetic fluid seals in high speed operation.The main works of the thesis are as follows:(1)The magnetic fluid suitable for high speed conditions is prepared.And the viscosity property is studied to obtain the visco-magnetic characteristic and the viscosity-temperature performance of magnetic fluid.The magnetization property of magnetic liquids at different temperatures is studied.(2)An experimental device of static magnetic fluid seal mechanism is designed and built to observe the change of liquid film.The shape of the magnetic fluid film in the seal gap is obtained by means of simulation and experiment for the first time,and a two-phase flow simulation method of magnetic fluid and air is proposed.The pressure transfer mechanism and failure mechanism of magnetic fluid seal are studied by means of simulation and experiment.The research indicates that the pressure of each chamber between the polar teeth increases successively in the process of pressure transfer.After the magnetic fluid film under the former tooth ruptures,the compressed gas enters the next chamber between the polar teeth,and the liquid film under the next tooth begins to be pressed.During the process of pressure transfer,the magnetic fluid liquid film ruptures and recovers several times,and the volume of magnetic fluid gradually decreases.The research indicates that the failure of magnetic fluid seal is divided into two stages:micro-leakage stage and complete rupture stage.(3)The magnetic field,temperature field and flow field of the magnetic fluid seal are simulated under high speed condition.The effect of temperature and centrifugal force on magnetic liquid seal is analyzed quantitatively for the first time.The magnetic fluid liquid film is continuously in the cycle of being thrown out and being attracted back to the seal clearance under the action of centrifugal force and magnetic field force.With the increase of rotating speed,the centrifugal force on the magnetic fluid increases,and the temperature increases,which leads to the decrease of saturation magnetization,the magnetic liquid liquid film is more easily broken through,and the sealing performance of the magnetic fluid decreases.(4)The high speed magnetic fluid seal test bench is set up,The effect of high line velocity on the seal capacity of magnetic liquid seal is studied by quantitative experiment for the first time.When rotation speed reaches to 8000 rpm,the linear velocity of the rotating shaft is 20.1m/s,the forced convection heat transfer reduces a magnetic fluid temperature of 75 ?.And the seal capacity of magnetic fluid seal under cooling condition is increased by 53kPa compared with it under no cooling condition.