Study On The Internal Flow Field Characteristics Of Wastewater Hydrocyclone Anti-blocking Machine With Ejector

With China's “peak carbon emissions by 2030 and achieve carbon neutrality by2060” proposed,the reduction of building energy emissions has attracted more and more attention.Recycling the huge low-level thermal energy in urban sewage is an effective means to reduce the primary energy consumption of buildings.However,the sewage source heat pump is limited by the operational reliability and maintenance economy of the decontamination device in the process of sewage heat extraction,which makes the technology of sewage purification and heat extraction still face great challenges.Aiming at continuous operation,high performance,and low energy consumption of the wastewater hydrocyclone anti-blocking machine with ejector(WHAME),this thesis reveals the reasons for the performance change from the perspective of its internal flow field characteristics,and improve the performance of the ejector device,and reduce energy consumption through the turbulence field control method.Further,we analyzed the method of improving performance from separation law and mechanism,and it lay the foundation for machine development and design.First of all,the relevant theoretical analysis involved in the hydrocyclone flow field found that whether the particles are separated is greatly affected by the drag force of the fluid except their density.The particle separation efficiency can be improved by adjusting or controlling the flow of the liquid.The ejection intensity is coupled with the split ratio,so the optimization design of the ejector structure may be an effective way to improve the separation efficiency.The Locus of Zero Vertical Velocity(LZVV)can isolate the inner and outer swirling flows,which will weaken the conversion caused by the turbulence.And then through the derivation and discussion of Einstein's rheological equation,it is found that the concentration of particulate matter will change the viscosity of the liquid.In WHAME,the viscosity of external swirling flow and internal swirling flow will be different due to the concentration of particles contained.To investigate the different flow field distribution,it is necessary to measure the rotating flow field with different viscosities fluid.Third,by improving the design of the combination of the ejector and the underflow device,the ejector was changed to adjust the turbulent flow field.The experiment tested by the sewage and mixture water(tap water and particles have the similar density),we found that: in the ejector with an underflow pipe,the separation efficiency,split ratio,and energy consumption increased with the increase of reflux angle;in the ejector without an underflow pipe,the separation efficiency and ejection coefficient decreased with the increase of the reflux angle,but the system energy consumption increased instead.In addition,the isodiametric blowdown pipe has higher separation efficiency than the divergent blowdown pipe,but the energy consumption also increases,and the split ratio is relatively large.Therefore,to simplify the structure of WHAME,the ejection device without the underflow pipe should be preferred in the design and application.When the bottom installation space is large,the isodiametric blowdown pipe should be chosen(small reflux angle,inclination).When the space is limited,the divergent blowdown pipe is good(large reflux angle,small inclination).Fourth,the turbulent energy consumption can be decreased through flow field intervention(insert cone).The original virtual LZVV was materialized by inserting a cone at the LZVV.The effect of the cone height,position,and inlet velocity on the separation performance was investigated.The results show that the energy consumption of inserting the cone in the LZVV is about 40% lower than that of the traditional hydrocyclone without a cone,and the separation efficiency is increased by about 5%.Through the single factor experiment and the response surface method interaction combination experiment on the cone height,the reflux angle,and the insertion depth of the vortex finder,the effects on the separation efficiency and the total pressure drop are investigated.It is found that these three factors have significant effects on separation performance,but their interaction is not significant.The maximum separation efficiency of WHAME is 94.85%,and the minimum total pressure drop is 1.02 k Pa.Then,the flow field was observed by the particle image velocimetry(PIV)method,and it was found the axial velocity distribution has changed from two parts to three: the underflow downward along the wall,the underflow downward along the center,and the upward overflow between the two.The negative axial velocity in the center can reach the bottom of the vortex finder.The split ratio and total pressure drop of WHAME are larger than those of the traditional one.But it will decrease with the increase of the reflux angle because the fluid mixing process caused by the ejection will lose a large amount of energy.At the same time,the measurement of the influence of the rheological properties of the medium on the flow field found that the flow field has nothing to do with the Newtonian and non-Newtonian properties of the fluid,but the viscosity of the fluid itself has a great influence on the ejection effect.The concentration of Newtonian and non-Newtonian fluids mainly affects the flow field that is concentrated in the cone section(z =-56 mm or less),there is almost no effect on the outside of LZVV.Finally,numerical simulation methods were used to make up for the working conditions that are not easy to observe in the experimental operation and flow field visualization measurement.It is found that because of backpressure,the increase of the reflux angle will weaken the ejection effect of the overflow-suck-underflow,which is more pronounced in the divergent blowdown pipe.The study of the flow field inserts shows that the long cone has a more suppressive effect on the turbulence.The turbulence is the most intense when the position of the insert cone moves to the bottom of the outer cone.The turbulence is strongest.Inserting the cone can effectively suppress the turbulence and reduce the pressure drop.However,the insert cone should not be installed too low to prevent touching the inner wall of the cone to form an inverted flow and lose the separation effect.To summarize,this thesis starts with the analysis of the internal flow field of the hydrocyclone and reveals the mechanism of changing the structure parameters to improve the separation performance.In turn,the flow field is adjusted by inserting a cone,which affects its turbulence intensity and improves the performance.This lays the foundation for the design and development of WHAME and provides ideas for the measurement and regulation of traditional rotating flow fields.It will help the understanding of swirling separation and promote its application in the field of heat energy recovery.This thesis is part of the project of "Study on the Mechanism of hydrocyclone Separation Enhanced by Ejector",which is supported by the National Natural Science Foundation of China(No.51978200).