Flow Field And Sediment Motion Simulation Study Of Flap Mesh Filter

Object:Mesh filter is one of the commonly used filters in agricultural economical irrigation,but for the characterization of particle deposition in the mesh filter,the filter cake pressure drop model,and the cleaning theory need to be perfected.Therefore,this thesis takes the flap screen filter as the research object,and conducts systematic research on the hydraulic characteristics of the screen filter,the movement of sediment particles and the cleaning theory,in order to provide more efficient and energy-saving self-cleaning screen filters.The stable and high-efficiency operation and structural optimization of the mesh filter provide theoretical guidance.Method:Use Fluent software to simulate the filtration process and cleaning process of the flap screen filter under the condition of clear water,and obtain its internal flow field,pressure field,flow velocity and pressure distribution inside and outside the filter screen;use CFD-DEM coupling to simulate the flap screen filter The movement of sediment particles under the condition of sandy water source is used to determine the particle distribution of the filter screen;the calculation model of filter cake pressure drop is established by using the Carman-Kozeny equation;the optimal cleaning flow model is established by using the theory of accumulation velocity in heterogeneous pipeline flow.Results:(1)During the filtration process,the tank body has four characteristic flow velocity regions and pressure regions.The flow velocity and pressure of the tank body along the axial direction gradually decrease.As the inlet flow increases,the greater the flow velocity and pressure in the characteristic region,the lower filter screen,The difference of the peak flow velocity on the outside increases,and as the aperture of the filter increases,the peak pressure difference between the inside and outside of the filter and the peak flow velocity inside the filter increase.During the cleaning process,the tank body has three characteristic flow velocity areas and pressure areas.As the inlet flow increases,the peak flow velocity and pressure inside the filter gradually increase.As the pore size increases,the peak flow velocity inside the filter and the inside of the filter The outer peak pressure difference increases;(2)Simulation of water and sand movement during the filtration process:(1)The sediment particles of the three types of screen filters gradually increase along the axial direction,and the proportion of small particles along the axis gradually increases,while the medium-sized The proportion of particles and large particles showed a gradually decreasing trend;the filter cake structure along the axis accounted for mainly small particles(more than80%),and the closer to the outlet,the thicker the filter cake.(2)The larger the inlet flow rate of the mesh filter,the larger the filter cake area,the more uneven the axial distribution of the filter cake,and the average particle size and geometric standard deviation of the filter cake particle distribution increase with the increase of the flow rate;the higher the particle concentration The more the number of deposits,the greater the thickness of the filter cake;the concentration has no significant effect on the average particle size and geometric standard deviation of the filter cake particles.(3)The calculated pressure drop is basically consistent with the test pressure drop.The filter cake pressure drop decreases with the increase of geometric standard deviation and average particle size.The filter cake pressure drop model can reflect the influence of filter cake characterization on filter cake pressure drop.(3)Simulation of water and sand movement and structural optimization during the cleaning process of the flap screen filter:(1)There are a small range of agglomerated sediment particles that are not thoroughly cleaned in the inlet section.With the increase of the cleaning flow rate,the agglomerated sand particles gradually The mesh particles can be stably attached to the upper filter,and the upper and lower filters are cleaned at the same time,which improves the cleaning efficiency;(2)Under the same flow rate,the smaller the proportion of particles before and after turning over the plate,the lower the residual degree,and the greater the particle concentration,the cleaning The more particles are left behind.(3)The length-to-diameter ratio of the tank is 4.25,and the best cleaning flow rate range is 188～199m~3/h,and the best flap position is 0.3～0.4 on the axis;(4)Particles remain in the vortex area,reducing the concentrated distribution of particles in the inlet section.Conclusion:The degree of particle residue after cleaning is affected by the particle distribution characteristics of the filtration process,but the particle distribution characteristics of the filtration process are mainly affected by the filtration flow rate and tank structure.Therefore,in the actual production,the screen filter for segmental filtration should be selected according to the commonly used irrigation flow range and the length-to-diameter ratio of the tank,and the appropriate segment position should be selected.The tank body and the water inlet pipe should adopt a smooth gradient structure to reduce eddy currents.