Study Of Fluid Mechanics Characteristics Of Filter Head Air-water Backwashing

Filtration is the necessary process to ensure the safety of drinking water. Effectivebackwash is the key to guarantee the stability of operation of the filter. Based on thedevelopment and application status of backwash technology in conventional treatmentprocess, it is determined that the hydraulic characteristics of the nozzle strainers whichis widely used in the process of air-water backwash being as the research content in thispaper. The flow resistance and pressure distribution of the nozzle strainers is studied,the characteristics of nozzle strainers’ working condition under different backwashintensity is ascertained. So as to provide the basis for the optimization of gas waterbackwash system.The method of computational fluid dynamics (CFD) theoretical calculation andexperimental detection are combined，on the basis of FLUENT simulation and filtercolumn model, the hydraulic characteristics of the nozzle strainers is discussed, theresearch conclusion includes:(1)The numerical simulation results shows that, the head loss of the filter-cap isdetermined by the gap velocity,with no relation to the forms of the filter-cap. therelationship between the velocity and the head loss under different open-area ratio agreewell with the experimental results.(2) The pressure balance of the gas and water in the gas-water distribution chamberis established, the simulation data and the experimental results reveals that under thecondition of single gas back flush, piezometric tube difference generally has nothing todo with the gas inflow. When the air entered through both the air-pore and the gap,the negative value of the piezometric tube difference is basically in direct proportion to thegas inflow.Under the conditions of air-water backwash,with a certain water inflow, thepiezometric tube difference when the gas entered through the air-pore was greater thanthat when the air entered through both the gas-pore and the gap.(3) According to the established mathematical model, with reference to theproduction practice，the range of backwash intensity is determined, the formularevealing the relation of the water depth in gas-water distribution chamber to the waterinflow and air inflow in both single gas backwash case and air-water backwash case arededuced. Which could provide certain theoretical basis for improving the performanceof filter by adjusting the intensity of gas and water.