Numerical Studies On Flow Field Characteristics And Suspended Particle Migration In Horizontal Sedimentation Tank

As a commonly-used solid-liquid separation unit,the horizontal sedimentation tank plays an irreplaceable role in the water treatment plant.It is suitable for many types of water treatment plants for its characteristics of stable operation,strong impact load,and good effluent quality.However,there are many problems during the actual project operation such as uneven water distribution and poor outflow water quality.With the continuous improvement of urban water plant construction,how to optimize the design and make it highly efficient is of great significance.Based on the three-dimensional model of the horizontal sedimentation tank by using computational fluid dynamics(CFD)software,the optimization of the internal structure of the water distribution channel and the design of the finger-type gutter would achieved in this paper through the orthogonal test design method.This would provide theoretical guidance for optimal design parameters and efficient operation of actual structures.For the problem of unequal flow velocity distribution in perforated walls of structures and unequal distribution of flow in each corridor,the flow field is simplified into single-phase flow,the structure of the guide wall in the distribution channel is refined.The distance L2 from the side wall,the radius r,the length of the straight part L1 and the distance D from the outlet are changed by analyzing the variance of the velocity distribution of the perforated wall and the index of the uniformity of the distribution of the flow of the corridor.According to orthogonal test analysis method,the order of the significant influence of each factor is:the radius of arc section>the shape of the guide wall>the distance from the sidewall>the length of the straight part.So the optimum combination and optimization scheme for the guide wall structure is determined as follows:Arc,L2=0.6m,r=0.77m,L1=0.34m,And under the optimized scheme,the standard deviation of the velocity distribution of the perforated wall hole is 0.01067,and the flow uniformity index rQ=0.9635.When the influent flow rate is fixed,the effluent quality is also affected by the overflow effluent tank setting method.The finger-type flumes was selected in this article,the removal rate was slectedas the evaluation index by changing the length of the finger flutes,the number of strips,the width of the trenches.Through the orthogonal test analysis method,the order of significance of all factors was:total tank length>slot width>number of slots,and the optimal combination optimization plan for designing the type of sink was:seven slots,the total slots length is 33.4 meter,and the groove width is 0.34m.And get the removal rate is 94.89%.Due to the actual operation of the simulation results may have some differences,but those can provide guidance for the optimization of the structure,and we cannot solely rely on experience and individual subjective choices in the design process.According to water quality and the characteristics of the structures themselves,we should set relevant parameters reasonably to achieve the best results.