Turbulent agglomeration is a promising pretreatment technology for improving the removal of fine particles in industrial flue gas,which can improve the particle removal effect of dust removal equipment safely and econ...Turbulent agglomeration is a promising pretreatment technology for improving the removal of fine particles in industrial flue gas,which can improve the particle removal effect of dust removal equipment safely and economically.However,due to the complexity of turbulence mechanisms,the relationship between turbulent flow fields and the agglomeration of fine particles is not known with precision,resulting a weak promotion effect for particle removal with this pretreatment technology.In this work,three kinds of turbulent agglomerators were constructed to investigate the agglomeration and removal characteristics of fine particles under different turbulent flow fields.The results demonstrated that the turbulent agglomerator with small-scale and three-dimensional vortexes in the flow field had the best effect in improving the agglomeration and removal of fine particles.Two kinds of agglomeration modes in turbulent agglomeration were proposed,one being agglomeration between fine particles in the vortex area,and the other the capture of fine particles by coarse particles.Furthermore,the motion trajectory,relative velocity and residence time of fine particles of different sizes in different flow fields were calculated by numerical simulation to investigate the interaction mechanism of particle agglomeration and turbulent flow fields.The results showed that a flow field with smallscale and three-dimensional vortexes can reduce the Stokes number(StK) and the relative velocity of particles of different sizes,and extend their residence time in a turbulent flow field,so as to obtain a better agglomeration effect for fine particles.展开更多
A vortex electrostatic precipitator （VEP） forms a vortex flow field within a precipitator by means of the vertical staggered layout of the double-vortex collecting plate facing the direction of the gas flow. The ion...A vortex electrostatic precipitator （VEP） forms a vortex flow field within a precipitator by means of the vertical staggered layout of the double-vortex collecting plate facing the direction of the gas flow. The ion concentrations within the precipitator can be significantly increased. Correspondingly, the charging and coagulation rates of fine particles and particle migration velocity are significantly improved within the VEP. Since it can effectively collect fine particles and reduce precipitator size, VEPs represent a new type of electrostatic precipitator with great application potential. In this work the change curve of the external voltage, gas velocity, row spacing and effective collecting area influencing the precipitation efficiency were acquired through a single-factor experiment. Using an orthogonal regression design, attempts were made to analyze the major operating parameters influencing the collecting efficiency of fine particles, establish a multiple linear regression model and analyze the weights of factors and then acquire quantitative rules relating experimental indicators and factors. The regression model was optimized by MATLAB programming, and we then obtained the optimal factor combination which can enhance the efficiency of fine particle collection. The final optimized result is that： when gas velocity is 3.4 m s-1, the external voltage is 18 kV, row spacing is 100 mm and the effective collecting area is 1.13 m2, the rate of fine particle collection is 89.8867%. After determining and analyzing the state of the internal flow field within the VEP by particle image velocimetry （PIV）, the results show that, for a particular gas velocity, a vortex zone and laminar zone are distinctly formed within the VEP, which increases the ion transport ratio as well as the charging, coagulation and collection rates of fine particles within the precipitator, thus making further improvements in the efficiency of fine particle collection.展开更多
Experimental studies which focus on flow visualization and the velocity field of a supersonic laminar/turbulent flow over a compression ramp were carried out in a Mach 3.0 wind tunnel. Fine flow structures and velocit...Experimental studies which focus on flow visualization and the velocity field of a supersonic laminar/turbulent flow over a compression ramp were carried out in a Mach 3.0 wind tunnel. Fine flow structures and velocity field structures were obtained via NPLS （nanoparticle-tracer planar laser scattering） and PIV （particle image velocimetry） techniques, time- averaged flow structures were researched, and spatiotemporal evolutions of transient flow structures were analyzed. The flow visualization results indicated that when the ramp angles were 25~, a typical separation occurred in the laminar flow, some typical flow structures such as shock induced by the boundary layer, separation shock, reversed flow and reattachment shock were visible clearly. While a certain extent separation occurred in turbulent flow, the separation region was much smaller. When the ramp angles were 28~, laminar flow separated further, and the separation region expanded evidently, flow structures in the separation region were complex. While a typical separation occurred in turbulent flow, reversed flow structures were significant, flow structures in the separation region were relatively simple. The experimental results of velocity field were corresponding to flow visualization, and the velocity field structures of both compression ramp flows agreed with the flow structures well. There were three layered structures in the U component velocity, and the V component velocity appeared like an oblique ＂v＂. Some differences between these two compression ramp flows can be observed in the velocity profiles of the shear layer and the shearing intensity.展开更多
Air pollution caused by particles with small size has been a global concern because of threats to human health.A feasible way to remove these super fine suspended particles is using electrostatic precipitation technol...Air pollution caused by particles with small size has been a global concern because of threats to human health.A feasible way to remove these super fine suspended particles is using electrostatic precipitation technology.Herein,the PIV was used to measure the particle velocity distribution.By analyzing the particle motion trend in high electric field,a process of particle charging loss was observed.This phenomenon cannot be explained by current particle charging theories.Our conclusions may improve the understanding of particle charging processes.展开更多
基金supported by the National Key Research and Development Program of China (No.2016YFB0600602)the National Natural Science Foundation of China (No.51806107)the Scientific Research Foundation of Graduate School of Southeast University (No.3203009749).
文摘Turbulent agglomeration is a promising pretreatment technology for improving the removal of fine particles in industrial flue gas,which can improve the particle removal effect of dust removal equipment safely and economically.However,due to the complexity of turbulence mechanisms,the relationship between turbulent flow fields and the agglomeration of fine particles is not known with precision,resulting a weak promotion effect for particle removal with this pretreatment technology.In this work,three kinds of turbulent agglomerators were constructed to investigate the agglomeration and removal characteristics of fine particles under different turbulent flow fields.The results demonstrated that the turbulent agglomerator with small-scale and three-dimensional vortexes in the flow field had the best effect in improving the agglomeration and removal of fine particles.Two kinds of agglomeration modes in turbulent agglomeration were proposed,one being agglomeration between fine particles in the vortex area,and the other the capture of fine particles by coarse particles.Furthermore,the motion trajectory,relative velocity and residence time of fine particles of different sizes in different flow fields were calculated by numerical simulation to investigate the interaction mechanism of particle agglomeration and turbulent flow fields.The results showed that a flow field with smallscale and three-dimensional vortexes can reduce the Stokes number(StK) and the relative velocity of particles of different sizes,and extend their residence time in a turbulent flow field,so as to obtain a better agglomeration effect for fine particles.
基金sponsored by the National Natural Science Foundation of China(grant no.51278229)the Six Talent Peak Project of Jiangsu Province(grant no.JNHB-018)
文摘A vortex electrostatic precipitator （VEP） forms a vortex flow field within a precipitator by means of the vertical staggered layout of the double-vortex collecting plate facing the direction of the gas flow. The ion concentrations within the precipitator can be significantly increased. Correspondingly, the charging and coagulation rates of fine particles and particle migration velocity are significantly improved within the VEP. Since it can effectively collect fine particles and reduce precipitator size, VEPs represent a new type of electrostatic precipitator with great application potential. In this work the change curve of the external voltage, gas velocity, row spacing and effective collecting area influencing the precipitation efficiency were acquired through a single-factor experiment. Using an orthogonal regression design, attempts were made to analyze the major operating parameters influencing the collecting efficiency of fine particles, establish a multiple linear regression model and analyze the weights of factors and then acquire quantitative rules relating experimental indicators and factors. The regression model was optimized by MATLAB programming, and we then obtained the optimal factor combination which can enhance the efficiency of fine particle collection. The final optimized result is that： when gas velocity is 3.4 m s-1, the external voltage is 18 kV, row spacing is 100 mm and the effective collecting area is 1.13 m2, the rate of fine particle collection is 89.8867%. After determining and analyzing the state of the internal flow field within the VEP by particle image velocimetry （PIV）, the results show that, for a particular gas velocity, a vortex zone and laminar zone are distinctly formed within the VEP, which increases the ion transport ratio as well as the charging, coagulation and collection rates of fine particles within the precipitator, thus making further improvements in the efficiency of fine particle collection.
基金supported by the National Natural Science Foundation of China(Grant Nos.11172326 and 11302256)
文摘Experimental studies which focus on flow visualization and the velocity field of a supersonic laminar/turbulent flow over a compression ramp were carried out in a Mach 3.0 wind tunnel. Fine flow structures and velocity field structures were obtained via NPLS （nanoparticle-tracer planar laser scattering） and PIV （particle image velocimetry） techniques, time- averaged flow structures were researched, and spatiotemporal evolutions of transient flow structures were analyzed. The flow visualization results indicated that when the ramp angles were 25~, a typical separation occurred in the laminar flow, some typical flow structures such as shock induced by the boundary layer, separation shock, reversed flow and reattachment shock were visible clearly. While a certain extent separation occurred in turbulent flow, the separation region was much smaller. When the ramp angles were 28~, laminar flow separated further, and the separation region expanded evidently, flow structures in the separation region were complex. While a typical separation occurred in turbulent flow, reversed flow structures were significant, flow structures in the separation region were relatively simple. The experimental results of velocity field were corresponding to flow visualization, and the velocity field structures of both compression ramp flows agreed with the flow structures well. There were three layered structures in the U component velocity, and the V component velocity appeared like an oblique ＂v＂. Some differences between these two compression ramp flows can be observed in the velocity profiles of the shear layer and the shearing intensity.
基金supported by the National Natural Science Foundation of China(Grant No.51107095)
文摘Air pollution caused by particles with small size has been a global concern because of threats to human health.A feasible way to remove these super fine suspended particles is using electrostatic precipitation technology.Herein,the PIV was used to measure the particle velocity distribution.By analyzing the particle motion trend in high electric field,a process of particle charging loss was observed.This phenomenon cannot be explained by current particle charging theories.Our conclusions may improve the understanding of particle charging processes.
