Design Of Rainwater Rapid Filter And Simulation Of Internal Flow Fiel

With the continuous acceleration of urbanization,a series of problems such as urban waterlogging,urban water pollution,and water resource shortage have also occurred one after another.The collection and utilization of rainwater can alleviate the aforementioned environmental problems to a certain extent.Based on this,this article constructs a roof rainwater collection and treatment system based on a rapid filter,and conducts research from two aspects:system design（physical size,filler type and ratio）and internal flow field simulation.The main conclusions of this article are as follows:The different types and ratios of fillers have a significant impact on the hydraulic conductivity and pollutant removal efficiency of the rapid filter.In the combined filter media of activated carbon,anthracite,activated carbon and quartz sand,with the increase of the volume proportion of activated carbon,the hydraulic conductivity of the rapid filter is reduced,and the removal efficiency of pollutants is gradually increased;In the combined filter media of anthracite and quartz sand,the higher the volume proportion of anthracite,the higher the hydraulic conductivity of the fast filter and the removal efficiency of pollutants;The volume ratio of anthracite and quartz sand is 3:2,which is the best combination filler for the rapid filter.Its permeability coefficient is 3.15 mm/s.The average removal efficiency of turbidity,TDS,NH₄⁺-N,TN,COD and DOM in roof runoff rainwater is 53.60%,53.81%,50.06%,35.65%,43.24%and 46.96%,respectively.The buffer volume of the rapid filter is mainly related to the rainfall return period,catchment area,cross-sectional area of the rapid filter,and filtration speed.During the period when the rainfall flow exceeds the treatment flow,a minimum buffer volume needs to be set to temporarily store the excess rainwater;Combining the Chicago rain pattern method to design the rainfall process,the designed rainfall runoff flow rate and volume show a trend of first increasing and then decreasing,and the larger the return period,the larger the rainfall flow rate and volume,and both reach the peak flow rate when the rainfall reaches 47 minutes;Taking Nanjing as an example,when the return period P=10 a,the rainfall duration is 120 minutes,the catchment area F=50 m²,and the filtration speed is v=1,2,3,and 4 mm/s,the minimum buffer volume required for the rapid filter is 2.383 m³,1.58 m³,1.074 m³,and 0.732 m³,respectively;Developing a buffer volume design program for fast filters using Python can effectively improve computational efficiency,accuracy,and universality.The main factors affecting the filtration performance and internal flow field of a rapid filter are the shape of the filter,the height to diameter ratio of the filter,the diameter of the inlet pipe,the inlet speed of the filter,and the height of the cushion layer;When the aspect ratio of the rapid filter increases from 1.4 to 3.0,the uneven distribution of the filter material in the cylindrical rapid filter decreases from 0.7386 to 0.4273,and the uneven distribution of the filter material in the square rapid filter decreases from 0.7592 to 0.4491;When the diameter of the inlet pipe of the filter increases from 10 cm to 30 cm,the unevenness of the filter material decreases from 0.7161 to 0.3486,and the pressure drop increases from 104.205 Pa to 967.869Pa;The inlet velocity of the filter has little effect on the non-uniformity of the filter material.When the inlet velocity increases from 0.02 m/s to 0.10 m/s,the pressure drop increases from267.53 Pa to 1336.59 Pa;By optimizing the size simulation of the fast filter,it was found that for a fast filter with a processing capacity of 12 m³/h,the optimal size of the fast filter is a cylindrical shape,a height to diameter ratio of 2.58,a diameter of 22.36 cm for the inlet pipe,a velocity of 0.02 m/s,and a cushion height of 18 cm.The research results of this article are beneficial for promoting the further development of urban roof rainwater utilization and providing reference for improving the urban rainwater management system.