Study On Numerical Simulation Of Spiral Flow Mixing Technology For Booster Chlorination Of Pipe Network

Booster chlorination of water distribution system is a reasonable improvement on the traditional water disinfection process.Adding some points to the pipe network in different location regularly not only reduces the concentration of the dosing at the first point,but also ensures that the chlorine concentration in the follow-up pipes meets the minimum requirements.The booster chlorination system is basically free of mixed parts at the present stage,thus it results the drug distribution uniformity and poor stability after dosing points in the network;moreover,the hydraulic loss of the pipe mixing devices widely used is too large.These devices have a poor applicability to the construction of the booster chlorine system,especially to the fixed pressure transformation of the pressure pump project.Therefore,it is of great practical significance to develop a hydraulic mixing device with fast,uniform and low water head loss for the large number of multi-point remediation projects of pipe network our country faces.Based on the spiral flow mixing technology,this study was intended to develop a tube-type mixing device,which can accelerate chlorine dissolution and lower its loss.Based on Computational Fluid Dynamics,Solidworks was used to build the geometric model of DN=100mm and Fluent was used to simulation calculation.Through the combination of computer numerical simulation and theoretical analyzing,the mixing performance and flow characteristics of the mixing device was estimated.The influence of the key structure parameters on the mixing effect and the pressure loss of the mixing device,such as the number of guide vanes,the angle of the guide vanes,the length of the guide vanes and the height of the guide vanes were investigated,and the orthogonal experiment was used to optimize these key parameters.The main conclusions of the study were as follows:1.The flow line of the fluid changes after flowing through the mixing device,and the moving pattern of fluid changes from one-dimension to three-dimension.Because of the pressure difference between the surface of the blade and the back surface of the pipe,the fluid flows from the high pressure area to the low pressure zone,the velocity direction was changed and the convective mixing was accelerated.In addition,the vortex flow was formed in the cross section of the pipe by the action force of the blade to the fluid at the position of the blade near the axis of the tube,thus the radial mixing of the medicament was promoted.2.Through the single factor experiments,it was found that the optimum number of guide vanes for the mixing effect is 3.The mixing effect is enhanced rapidly with the increasing of wrap angle range from 20°~30°.When the angle was more than 30°,the mixing effect tends to be stable.The mixing effect can be improved by increasing the length of the straight section of the blade in the range of 0.25 ~ 0.5 times of the total length.The higher the height of guide vanes are,the better the mixing effect is,moreover,the pressure loss also increased.3.Through orthogonal experimental analysis found that,the influence of the structural parameters of the blade on the mixing effect was the number of guide vanes > the angle of the guide vanes > the length of the guide vanes > the height of the guide vanes,the influence on the loss of resistance were the number of guide vanes > the height of the guide vanes > the angle of the guide vanes > the length of the guide vanes.The optimal parameters were 4 for the leaves,30 ° for the angle of the leaves,20 cm for the length of the leaves and 35 mm for the height.4.Through the numerical simulation of the optimum orthogonal experimental parameters which were 4 for the leaves,30 ° for the angle of the leaves,20 cm for the length of the leaves and 35 mm for the height,it was found that the COV value of the outlet section of the mixing device can reach 0.055,and the pressure loss was 181 pa.5.After the optimization of the dosing method in the original mixing device,it was found that the cross section concentration increases from 0.456 to 0.369 at Z = 2m,and the mixing effect was increased by 0.067 in the Z = 3m cross section,which satisfies the expected optimization target.6.The energy loss of the water flowing through the mixing device can be divided into the local resistance loss caused by the mixing device,loss of resistance along the resistance and conversion into rotational kinetic energy.The axial velocity distribution of the helical flow has the characteristic of logarithmic distribution.The circumferential velocity was symmetrical with respect to the tube axis,and the velocity peak of the circumferential velocity decreases with the attenuation of the swirling flow.Due to the turbulence of the fluid,the radial velocity distribution was less regular and the radial velocity was greatly influenced by the centrifugal force.7.The influence of the spiral flow mixing device on the hydraulic loss after the water supply pipe network was analyzed,and the hydraulic loss of the optimal mixing model was calculated.Compared with the traditional static mixer,when the spiral flow mixing device achieves uniform mixing of drugs,hydraulic loss was about 1.4 times the empty tube.It was more suitable for water supply pipe network.By comparing the calculated pressure loss with the numerical data and the simulated data,it was found that studying the spiral flow mixing device by numerical simulation is a desirable method.The results not only provide the theoretical guidance for the optimal manufacture of the hybrid device and the practical application in the pipe network,but also provide reference value for the future development and design of similar products.