Research On Agricultural Water Filtration Technology And Equipment In Karst Areas

In terms of water conversation in agricultural irrigation,it is necessary to add filtering equipment at the head of the irrigation system to filter the water source because blocking is easy to happen as a result of the small channel size of the emitter.As the key equipment of irrigation system,the performance of filter directly affects the normal operation of the whole irrigation system.The study on the working performance and influencing factors of the filter is of important guiding significance and practical value for the long-term normal and stable operation of the irrigation system.This thesis summarizes the research progress of common filtration equipment at home and abroad from aspects of theoretical analysis,numerical simulation and equipment test.On the basis of previous studies,an automatic backwashing sand filter suitable for mountain agriculture is designed,and the hydraulic performance tests of the filter under different flow rates are carried out.Combined with the computer fluid simulation software FloEFD,The numerical simulation of the whole flow field was carried out on the automatic backwashing sand filter.The main research work and conclusions are as follows:(1)Based on the porous media model,the whole flow field of the filter is numerically simulated by using the FloEFD fluid simulation software.The simulation results show that the internal flow of the filter is complex.Affected by the internal components(water distributor,sand filter layer,water filter cap)and the position of the inlet and outlet,the internal flow of the filter is not uniform,and exists vortices and reflux phenomena,which lead to the head loss of the filter.(2)The structure of the inlet and outlet position of the automatic backwashing sand filter is optimized,and three different structural schemes are discussed.Through the comparative analysis of the velocity nephogram,head loss and flow diagram,it is found that scheme a is more uniform in the velocity distribution than other schemes,so that the filter layer can be fully utilized,the filtering time of the filter can be prolonged,and the working efficiency of the filter can be improved.At the same time,the arrangement mode and number of filter caps are discussed.With the increase of the number of filter caps,the velocity variation range on the surface of the filter layer gradually decreases.From the same number of P31 series with different arrangements,it is found that the flow distribution around the center is more uniform and the velocity variation range is smaller.(3)Under the condition of clear water,the hydraulic performance of the filter is tested and studied,and the curves of the change of the filter and the head loss under different flow rates are obtained.It is concluded that the local head loss of the filter increases with the increase of the inflow flow rate.The maximum relative error of the head loss between the simulation results and the test results is 8.89%,less than 10%,the mean square error ERMS =0.00112,and the correlation coefficient R2 = 0.98,which indicates that the analysis model adopted and parameter setting are reasonable.(4)The hydraulic performance test of the optimized filter is carried out under the condition of clear water and muddy water.Through the comparative analysis of the test,it is found that the head loss of the optimized filter is 9.5% less than that of the filter before optimization,the sudden change of the cross section is reduced,and the stability of the internal flow field is maintained.In the muddy water test,it is found that the head loss and flow of the optimized filter change slowly with time.When the flow rate is reduced to 25%,the optimized filter can run for about 10 minutes more,which improves the performance of the filter and achieves the purpose of optimization.