Transient Characteristics Of Mechanical Seal Of Multiphase Pump Under The Condition Of Gas-liquid Mixed Transportation

Gas-liquid multiphase pump is an important equipment for marine oil-gas mixed transportation,which is widely used.The output of oil well is a mixture of oil,gas,water and a small amount of sand.The change of transmission medium will lead to the fluctuation of gas content at the inlet of multiphase pump.In this paper,the transient characteristics of mechanical seal under the condition of inlet void fraction fluctuation of multiphase pump are studied by numerical simulation.Firstly,aiming at the problem of micro particle deposition in the lubricating film of mechanical seal,a spiral groove liquid film model is established.Considering the cavitation of liquid film,DPM discrete phase model is used to study the transient deposition characteristics of micro particles in the sealing film.The results show that the solid particles mainly gather in the low pressure area in the tank,the particle diameter and rotating speed have a great influence on the particle deposition rate,and the particle density and inlet pressure have little influence on the particle deposition rate;Among the groove parameters,when the groove diameter ratio is 0.65 and the helix angle is 22 °,the particle deposition rate is the smallest,the film thickness has a great influence on the particle deposition rate,and the groove depth has a small influence.Secondly,aiming at the problem of severe pressure fluctuation in the pump caused by high gas content at the inlet of multiphase pump or slug flow condition,the pressure fluctuation is applied on the inner diameter side(static type)and outer diameter side(rotary type)of the seal ring respectively,and the anti-interference characteristics of the two mechanical seal forms under cavitation conditions are studied.The results show that there is a lag between the cavitation rate of liquid film and the fluctuation of boundary pressure,the synchronization of sealing performance parameters with the fluctuation of outlet pressure is good,and there is a phase difference with the fluctuation of inlet pressure;The larger the fluctuation of the membrane pressure and cavitation period,the greater the influence on the sealing performance of the membrane;The inner diameter side pressure fluctuation has a great impact on the end face cavitation and sealing performance,that is,the anti-disturbance characteristics of rotary mechanical seal are strong.Finally,aiming at the influence of pressure disturbance wave on the dynamic response of mechanical seal,the UDF(User Define Function)of compensation ring dynamics is compiled based on fluid structure coupling theory,and the layered dynamic grid technology is used to study the dynamic response characteristics of pressure disturbance wave on mechanical seal under cavitation conditions.The results show that the film thickness decreases gradually with the increase of disturbance amplitude and period,and the fundamental reason for the hysteresis of film thickness change is that the pressure in the high-pressure area of liquid film cannot be restored in time;The phase difference between leakage and axial velocity is π.The maximum value of leakage and the minimum value of axial velocity are determined by the disturbance amplitude and independent of the disturbance period;The mutual interference between enhancement waves has no obvious effect on the film thickness,while the attenuation wave can promote the change of film thickness;Compared with the pressure disturbance condition,the alternating load changes the film thickness and leakage more significantly.The research results obtained in this paper not only provide theoretical support for improving the structural design of mechanical seal of multiphase pump,but also provide guidance for the safe operation of multiphase pump under extreme working conditions.