Experimental Research On Movement And Deposition Of Fine Particles In Supercritical Water

In recent years,supercritical once-through boilers and supercritical nuclear power units have been the focus of research.However,the supercritical water erodes the pipe wall and forms fine particles corrosion products in the process of flowing in the equipment pipeline.Fine particles are deposited on the wall of the pipeline,especially at elbows and joints of the pipeline,under the action of external forces such as thermophoresis,gravity,inertia and turbulence.Fine particles deposited on the wall of the pipeline will accelerate the corrosion of the pipeline,which will shorten the service life of the equipment,and a certain amount of particles in the pipeline will pose a very serious threat to the impeller of the steam turbine,seriously affecting the safe operation of the steam turbine.It is very important to calculate and design the experimental bench for the movement and deposition of fine particles and to study the movement and deposition of particulate matter in supercritical water.Firstly,based on the principle of passive natural circulation,an experimental channel for natural circulation of particulate matter movement in supercritical water was designed.The experimental device uses two heating stages:preheating stage and heating stage and the experimental section is set at the exit of the heating section to measure the particle movement in the experimental section.According to the special characteristics of supercritical water,the particulate matter in supercritical water,the pipe shape in supercritical water experimental section,the window material in supercritical water experimental section and the observation method of particulate matter were selected and designed.Secondly,full-scale model of supercritical water experimental channel was built by PRO/E software.The whole experimental channel and experimental channel were meshed and simulated by ANSYS software.Considering the effects of gravity,thermophoresis force and pressure gradient force,the changes of temperature,pressure,velocity and particle concentration in supercritical experimental loop were studied.According to the numerical simulation,the channel of the experimental section is selected.Thirdly,the deposition rate of particulate matter in supercritical water experimental pipeline was calculated by procedure ECSP,and the deposition rate was obtained under different temperature,pressure,pipeline length,particle size and velocity.The variation of particulate matter deposition rate in supercritical water with different factors was quantitatively analyzed,and the importance of the main factors affecting the deposition rate in pipelines was analyzed by using the neural network method.Finally,an experimental platform for particulate movement and deposition in supercritical water was designed and built.The bench uses ultra-light hollow microspheres as particles,artificial sapphire as window material,narrow rectangular channel as experimental section and particle image velocimeter as particle measuring device.Through experiments and calculations,it is concluded that the pressure of supercritical water increases with the increase of temperature;the flow rate and pressure difference increase with the increase of temperature;the deposition rate of fine particles increases with the increase of temperature;increases first and then decreases with temperature near the critical point.;decreases with the increase of particle diameter and pipe length;increases first and then decreases with the increase of flow velocity.The order of importance of the main factors affecting the deposition rate of particulate matter in supercritical water is particle diameter>inlet velocity>inlet temperature>pipe length>pressure.The mechanism of particle collision based on surface viscous force in supercritical water and the mechanism of particle deposition based on physical property change of supercritical water are analyzed,which is dominated by thermophoretic force,buoyancy and gravity under natural circulation conditions.It provides a reference for pipeline management and safety analysis of supercritical boilers and nuclear power units.