Experiment And Simulation Of Iron Diffusion At Dead-end Water Distribution Branch Pipes

The water quality problem of “red water” was always concerned by people.The study about water quality model only considered the increasing concentration of ferrate causing by wall reaction during the process of water flow in water distribution network.While,it neglected the effect of dead-end branch pipes connecting with fire hydrants on the content of ferrate in water distribution network.The dead-end branch pipe had the characteristic of big water age and low dissolved oxygen,which can cause the accumulation of ferrous ion on the pipe.Besides,the ferrous ion was diffluent and can easily diffuse to the main pipe.Therefore,the veracity of existing water quality model estimating the distribution and change rule of ferrate will be affected by it.For the computational fluid dynamic(CFD),it can solve the control equation get arithmetic solution of fluid.Then,plotting the picture according to the arithmetic solution.Hence CFD can qualitative and quantitative study the flow problem.Therefore,the method of CFD was carried out to study the ferrous ion diffusion of dead-end branch pipe.Meanwhile,the formed numerical model will also be verified to keep veracity through experimental analysis.Due to the fact that many factors can affect the ferrous ion diffusion on dead-end branch pipe,the orthogonal experimental analysis was firstly performed to get the significance factor.The results showed that the length of dead-end branch pipe,the ferrous ion concentration of dead-end branch pipe,the diameter of dead-end branch pipe and the diameter of main pipe had very significative effect on the diffusion of ferrous ion by dead-end branch pipe.And the flow velocity of main pipe had significative effect.Then,the complete analysis was carried out to analyzed the decided significance factors.In the experiment,the influence of the decided significant factors on the diffusion of ferrous ions was analyzed by the numerical model.Results showed that the diameter of dead-end branch pipe and the ferrous ion concentration of dead-end branch pipe had positive effect on ferrous ion diffusion.The the diameter of main pipe had negative effect on it.The flow velocity of main pipe had little effect on it.While the the length of deadend branch pipe is shorter than 5.5m,it had positive effect on ferrous ion diffusion.When the the length of dead-end branch pipe is longer than 5.5m,it had little effect on ferrous ion diffusion.By introducing the theory of square cavity flow,it was found that the periodic inflow and outflow of dead end branch pipe were the main reason for the diffusion of ferrous ions.In addition,according to the results of the numerical model,regression analysis was carried out to obtain the specific relationship between the factors and the diffusion iron,and the application is carried out on this basis.In application,the iron distribution in the actual water supply network of Y city was calculated by using the normal water quality model and the improved water quality model.Before the improvement,the normal water quality model only considered the increase of iron content caused by pipe wall reaction.However,the improved water quality model not only considered pipe wall reaction,but also considered the diffusion of iron in the dead end branch pipe.Finally,the results of the normal water quality model and the improved water quality model were compared with the results of the actual pipe network.Through analysis,it was found that the improved water quality model can better simulate the distribution and variation of iron in the actual network than the normal water quality model.