The axial velocity distribution in a gas cyclone has been examined with two-dimensional particle image velocimetry (2D-PIV) and three-dimensional particle image velocimetry (3D-PIV) experiments in this study. Due ...The axial velocity distribution in a gas cyclone has been examined with two-dimensional particle image velocimetry (2D-PIV) and three-dimensional particle image velocimetry (3D-PIV) experiments in this study. Due to the limitation of 2D-PIV configuration, the contamination generated by the strong tangential velocity in the cyclone can be registered in the axial velocity detected by 2D-PIV. Efficient methods are proposed in this work to remove this contamination. The contamination-removed 2D-PIV data agree well with 3D-PIV results. The distributions of the axial velocity are also computed by the Reynolds stress model (RSM) and verified using the PIV experimental results. Reasonable agreements are obtained.展开更多
An analytical study of the flow and pressure fields inside a small-diameter dense-media cyclone is presented.The simulations were done with the help of the CFD software FLUENT.The following conclusions were reached:th...An analytical study of the flow and pressure fields inside a small-diameter dense-media cyclone is presented.The simulations were done with the help of the CFD software FLUENT.The following conclusions were reached:the tangential velocity tends to increase when moving from the center toward the exterior.The velocity then begins to decrease when the maximum velocity point is reached.The velocity field divides into two different sections;an inner swirling zone and an outer swirling zone.The axial velocity points down at the wall and gradually decreases toward the bottom.Continuing toward the bottom,the axial velocity passes through zero and then gradually increases in the opposite direction.In the cyclone's central zone,the pressure is negative and the suction of air allows an air column to be formed therein.At the center of the radial negative zone the pressure drops to its lowest value—phenomenon that has been verified by theoretical analysis.Some discrepancies between the observed data and the simulated data are noted when an analysis in made on a cyclone operating with either fresh water only or with water with added heavy particles.展开更多
Based on a series of numerical calculations, the behavior of flow field in obstructed square buoyant vertical jet is summarized and analyzed. Based on the axial line velocity distribution, the flow after the disc can ...Based on a series of numerical calculations, the behavior of flow field in obstructed square buoyant vertical jet is summarized and analyzed. Based on the axial line velocity distribution, the flow after the disc can be divided into three regions, i.e., recirculation region, transitional region and self-similar region The characteristic of selfsimilarity of upright velocity was validated. The three regions can also be distinguished based on the axial velocity. The axial velocity in self-similar region was found to obey the same law and the formula presented by introducing the velocity expression used by Chen and Rodi. The isolines of pressure on cross-sections of different heights were displayed and the production, expansion, breaking and disappearing of negative pressure regions were found.展开更多
At present in China, the cyclones are widely used in the dust removal ventilation system of boilers, industry furnaces or pits etc., because of their simple structure, long life and cost efficiency. In order to improv...At present in China, the cyclones are widely used in the dust removal ventilation system of boilers, industry furnaces or pits etc., because of their simple structure, long life and cost efficiency. In order to improve efficiency of the cyclones, new theoretical calculation method is very important. In this paper, the concept of down-flow quantity is introduced and new formula is deducted based on Kilven law and the work has done by Zhao Weizhong[1]. The formula is not only of advantage theoretically but also fit with experimental results quite well. On the basis, the effect of three-dimensional velocity distribution in the flow field within cyclones and other parameters on the grade-efficiency calculation are analyzed and a new equation for grade-efficiency estimation is introduced. The calculating accuracy of the equation is better than the others theoretically and experimentally.展开更多
The maximum-efficiency inlet velocity(MEIV)is a ceiling of inlet gas velocity that defines separation efficiency during cyclone design and operation.Experiment and computational fluid dynamics(CFD)simulation exhibited...The maximum-efficiency inlet velocity(MEIV)is a ceiling of inlet gas velocity that defines separation efficiency during cyclone design and operation.Experiment and computational fluid dynamics(CFD)simulation exhibited that an apex cone at the dust outlet can break the ceiling and improve the sepa-ration efficiency.The phenomenon is closely related to the effect of excessive high inlet gas velocity on the back-mixing escape of fine particles,which is the final result of back mixing,entrainment by the rapid upward airflow,and secondary separation of the inner vortex.In the center of the inner vortex,the airflow rotates slowly and moves rapidly upward.This elevator type of airflow delivers re-entrained particles to the vortex finder.A higher inlet gas velocity accelerates the elevator,causing more entrained particles to escape.This explains the decrease in efficiency at an excessively high inlet gas velocity.When an apex cone is installed at the dust outlet,the back-mixing is significantly weakened because the vortex core is bounded to the center of separator,while the transport effect of rapid upward airflow is weakened by the decrease in axial velocity in the center.Therefore,particle escape is weakened even at excessive high inlet gas velocities.Instead,the centrifugal effect is enhanced because of increased tangential velocity of the gas and particles.Consequently,the ceiling of inlet gas velocity is broken.展开更多
The formation of a cutting bed in an annulus involves safety problems in drilling especially in the horizontal well and the directional well. In this work, three axial laminar velocity field calculation models for the...The formation of a cutting bed in an annulus involves safety problems in drilling especially in the horizontal well and the directional well. In this work, three axial laminar velocity field calculation models for the power-law fluid in an annulus are modified by considering the effect of the cutting bed. The proposed models are employed to numerically simulate the annulus flow with the cutting bed. Verified by the experimental data in literature, all of them can be applied to the situation of the annulus flow with the cutting bed. The modified concentric annulus model enjoys the best performance, while the flat channel flow model has the worst performance.展开更多
An analytical solution of velocity profiles for Non-Newtonian fluids described by the power-law equation in axial laminar flow through eccentric annuli is presented.The expressions of limit velocities and contours of ...An analytical solution of velocity profiles for Non-Newtonian fluids described by the power-law equation in axial laminar flow through eccentric annuli is presented.The expressions of limit velocities and contours of equal velocity are obtained. The main approaches,claimed in this paper,are that the term T_(rz)/r in the differential equation of flow and the non-symmetrical velocity distribution about the geometric center of the radial clearance are considered.展开更多
Axial flow pump is a kind of typical pumps with rotor-stator interaction, thus the measurement of the flow field between impeller and guide vane would facilitate the study of the internal rotor-stator interaction mech...Axial flow pump is a kind of typical pumps with rotor-stator interaction, thus the measurement of the flow field between impeller and guide vane would facilitate the study of the internal rotor-stator interaction mechanism. Through a structural modification of a traditional axial flow pump, the requirements of particle image velocimetry(PIV) measurement are met. Under the condition of opt.0.8Q, the axial vortex is identified between impeller hub and guide vane hub, which is developed into the main flow and to affect the movement when the relative positions of impeller and guide vane at different flow rates are the same. Besides, the development and the dissipation of the tip leakage and the passage vortex in impeller passages are mainly responsible for the difference of the flow field close to the outer rim. As the flow rate decreases, the distribution of the meridional velocities at the impeller outlet becomes more non-uniform and the radial velocity component keeps increasing. The PIV measurement results under the condition of opt.1.0Q indicate that the flow separation and the trailing vortex at the trailing edge of a blade are likely to result in a velocity sudden change in this area, which would dramatically destroy the continuity of the flow field. Moreover, the radial direction of the flow between impeller and guide vane on the measurement plane does not always point from hub to rim. For a certain position, the direction is just from rim to hub, as is affected by the location of the intersection line of the shooting section and the impeller blade on the impeller as well as the angle between the intersection line and the rotating shaft.展开更多
Because the rotational current stabilizes the flame by creating a recirculation zone,it may increase the risk of reversal.For this reason,low-spin combustion is used to stabilize the flame while preventing flashbacks....Because the rotational current stabilizes the flame by creating a recirculation zone,it may increase the risk of reversal.For this reason,low-spin combustion is used to stabilize the flame while preventing flashbacks.Therefore,in this study,the combustion flow of methane gas in a low-swirl burner is simulated using a partially premixed combustion model.Furthermore,the fuel flow rate is considered constant.The research parameters include swirl angle(θ=35°–47°),equivalence ratio(φ=0.6–0.9)and inlet axial flow radius(R=0.6–0.7)and effect of these parameters on temperature distribution,flame length,flame rise length,velocity field,and streamlines of the number of pollutant species are investigated.The contours of streamline,temperature distribution,and velocity distribution are also presented for analysis of flow physics.The results show that with increasing the fuel-air ratio,the strength of the axial flow decreases,and the position of the maximum flame temperature shifts toward the inlet of the reactants.The results also reveal that by increasing the swirl angle of the flow,the position of the minimum velocity value(opposite to the direction of the axis)tends towards the outlet.The results also indicate that the maximum temperature of the combustion chamber increases with increasing the swirl angle,and inθ=35°,the maximum temperature is 1711℃and inθ=41°,this value is 1812℃.Finally,by increasing the swirl angle toθ=47°,the maximum flame temperature position is found at a considerable distance from the inlet and is 1842℃.展开更多
As a support material, zeolite can be used to promote the granulation process due to its high settable property and the ability to retain biomass on its surface. The present paper reports on the influence of zeolite a...As a support material, zeolite can be used to promote the granulation process due to its high settable property and the ability to retain biomass on its surface. The present paper reports on the influence of zeolite addition on the hydrodynamic behavior of an expanded granular sludge bed reactor(EGSB). Different models were applied to fit the flow pattern and to compare EGSB hydrodynamic performance with and without the addition of zeolite. The experimental data fit the tanks in a series model for zeolite bed height of 5 cm and upflow velocity of 6 m/hr.Higher axial dispersion degree(D/uL) was obtained at lower heights of zeolite. The real hydraulic retention time(HRTr) was increased with both increased zeolite bed height and increased upflow velocity. The short-circuit results for 5 cm of zeolite bed and 6, 8 and 10 m/hr upflow velocity were 0.3, 0.24 and 0.19 respectively, demonstrating the feasibility of using zeolite for a proper hydrodynamic environment to operate the EGSB reactor. The presence of zeolite resulted in the higher percentage values of dead zones, ranging from 12% to 24%.Zeolite addition exerted a positive effect on the hydrodynamics pattern for this technology being advantageous for the anaerobic process because of its possible contribution to better biofilm agglomeration, granule formation and substrate-microorganism contact.展开更多
文摘The axial velocity distribution in a gas cyclone has been examined with two-dimensional particle image velocimetry (2D-PIV) and three-dimensional particle image velocimetry (3D-PIV) experiments in this study. Due to the limitation of 2D-PIV configuration, the contamination generated by the strong tangential velocity in the cyclone can be registered in the axial velocity detected by 2D-PIV. Efficient methods are proposed in this work to remove this contamination. The contamination-removed 2D-PIV data agree well with 3D-PIV results. The distributions of the axial velocity are also computed by the Reynolds stress model (RSM) and verified using the PIV experimental results. Reasonable agreements are obtained.
基金Projects 2007AA05Z339 supported by the Hi-tech Research and Development Program of ChinaCPEUKF08-10 by the Key Laboratory Opening Fund of Coal Processing & Efficient Utilization,Ministry of Education of China
文摘An analytical study of the flow and pressure fields inside a small-diameter dense-media cyclone is presented.The simulations were done with the help of the CFD software FLUENT.The following conclusions were reached:the tangential velocity tends to increase when moving from the center toward the exterior.The velocity then begins to decrease when the maximum velocity point is reached.The velocity field divides into two different sections;an inner swirling zone and an outer swirling zone.The axial velocity points down at the wall and gradually decreases toward the bottom.Continuing toward the bottom,the axial velocity passes through zero and then gradually increases in the opposite direction.In the cyclone's central zone,the pressure is negative and the suction of air allows an air column to be formed therein.At the center of the radial negative zone the pressure drops to its lowest value—phenomenon that has been verified by theoretical analysis.Some discrepancies between the observed data and the simulated data are noted when an analysis in made on a cyclone operating with either fresh water only or with water with added heavy particles.
基金Project supported by the Planned Item for Excellent Young Teachers Invested by Education Ministry of China (No.2003-99)
文摘Based on a series of numerical calculations, the behavior of flow field in obstructed square buoyant vertical jet is summarized and analyzed. Based on the axial line velocity distribution, the flow after the disc can be divided into three regions, i.e., recirculation region, transitional region and self-similar region The characteristic of selfsimilarity of upright velocity was validated. The three regions can also be distinguished based on the axial velocity. The axial velocity in self-similar region was found to obey the same law and the formula presented by introducing the velocity expression used by Chen and Rodi. The isolines of pressure on cross-sections of different heights were displayed and the production, expansion, breaking and disappearing of negative pressure regions were found.
文摘At present in China, the cyclones are widely used in the dust removal ventilation system of boilers, industry furnaces or pits etc., because of their simple structure, long life and cost efficiency. In order to improve efficiency of the cyclones, new theoretical calculation method is very important. In this paper, the concept of down-flow quantity is introduced and new formula is deducted based on Kilven law and the work has done by Zhao Weizhong[1]. The formula is not only of advantage theoretically but also fit with experimental results quite well. On the basis, the effect of three-dimensional velocity distribution in the flow field within cyclones and other parameters on the grade-efficiency calculation are analyzed and a new equation for grade-efficiency estimation is introduced. The calculating accuracy of the equation is better than the others theoretically and experimentally.
基金supported by Fundamental Research Program of Shanxi Province(No.202203021211164)supported by the National Natural Science Foundation of China(No.22108262)+2 种基金Shanxi Province Science Foundation for Youths(No.20210302124600)Shanxi Province Foundation for Returness(No.2022-138)Fund Program for the Scientific Activities of Selected Returned Overseas Professionals in Shanxi Province(No.20220014).
文摘The maximum-efficiency inlet velocity(MEIV)is a ceiling of inlet gas velocity that defines separation efficiency during cyclone design and operation.Experiment and computational fluid dynamics(CFD)simulation exhibited that an apex cone at the dust outlet can break the ceiling and improve the sepa-ration efficiency.The phenomenon is closely related to the effect of excessive high inlet gas velocity on the back-mixing escape of fine particles,which is the final result of back mixing,entrainment by the rapid upward airflow,and secondary separation of the inner vortex.In the center of the inner vortex,the airflow rotates slowly and moves rapidly upward.This elevator type of airflow delivers re-entrained particles to the vortex finder.A higher inlet gas velocity accelerates the elevator,causing more entrained particles to escape.This explains the decrease in efficiency at an excessively high inlet gas velocity.When an apex cone is installed at the dust outlet,the back-mixing is significantly weakened because the vortex core is bounded to the center of separator,while the transport effect of rapid upward airflow is weakened by the decrease in axial velocity in the center.Therefore,particle escape is weakened even at excessive high inlet gas velocities.Instead,the centrifugal effect is enhanced because of increased tangential velocity of the gas and particles.Consequently,the ceiling of inlet gas velocity is broken.
基金Project supported by the National Science and Technology Major Project(Grant No.2016ZX05020-006)the National Natural Science Foundation of China(Grant No.U1762216)+1 种基金the National Key Basic Research Development Program of China(973 Program,Grant No.2015CB251200)the National Key Research and Development Program of China(Grant No.2017YFC0307304)
文摘The formation of a cutting bed in an annulus involves safety problems in drilling especially in the horizontal well and the directional well. In this work, three axial laminar velocity field calculation models for the power-law fluid in an annulus are modified by considering the effect of the cutting bed. The proposed models are employed to numerically simulate the annulus flow with the cutting bed. Verified by the experimental data in literature, all of them can be applied to the situation of the annulus flow with the cutting bed. The modified concentric annulus model enjoys the best performance, while the flat channel flow model has the worst performance.
文摘An analytical solution of velocity profiles for Non-Newtonian fluids described by the power-law equation in axial laminar flow through eccentric annuli is presented.The expressions of limit velocities and contours of equal velocity are obtained. The main approaches,claimed in this paper,are that the term T_(rz)/r in the differential equation of flow and the non-symmetrical velocity distribution about the geometric center of the radial clearance are considered.
基金Project supported by the National Twelfth Five-year Supporting Plan of China(Grant No.2011BAF14B01)the Priority Academic Program Development of Jiangsu Higher Education InstitutionsGraduate innovation program of Jiangsu Province(Grant No.CXLX12_0643)
文摘Axial flow pump is a kind of typical pumps with rotor-stator interaction, thus the measurement of the flow field between impeller and guide vane would facilitate the study of the internal rotor-stator interaction mechanism. Through a structural modification of a traditional axial flow pump, the requirements of particle image velocimetry(PIV) measurement are met. Under the condition of opt.0.8Q, the axial vortex is identified between impeller hub and guide vane hub, which is developed into the main flow and to affect the movement when the relative positions of impeller and guide vane at different flow rates are the same. Besides, the development and the dissipation of the tip leakage and the passage vortex in impeller passages are mainly responsible for the difference of the flow field close to the outer rim. As the flow rate decreases, the distribution of the meridional velocities at the impeller outlet becomes more non-uniform and the radial velocity component keeps increasing. The PIV measurement results under the condition of opt.1.0Q indicate that the flow separation and the trailing vortex at the trailing edge of a blade are likely to result in a velocity sudden change in this area, which would dramatically destroy the continuity of the flow field. Moreover, the radial direction of the flow between impeller and guide vane on the measurement plane does not always point from hub to rim. For a certain position, the direction is just from rim to hub, as is affected by the location of the intersection line of the shooting section and the impeller blade on the impeller as well as the angle between the intersection line and the rotating shaft.
文摘Because the rotational current stabilizes the flame by creating a recirculation zone,it may increase the risk of reversal.For this reason,low-spin combustion is used to stabilize the flame while preventing flashbacks.Therefore,in this study,the combustion flow of methane gas in a low-swirl burner is simulated using a partially premixed combustion model.Furthermore,the fuel flow rate is considered constant.The research parameters include swirl angle(θ=35°–47°),equivalence ratio(φ=0.6–0.9)and inlet axial flow radius(R=0.6–0.7)and effect of these parameters on temperature distribution,flame length,flame rise length,velocity field,and streamlines of the number of pollutant species are investigated.The contours of streamline,temperature distribution,and velocity distribution are also presented for analysis of flow physics.The results show that with increasing the fuel-air ratio,the strength of the axial flow decreases,and the position of the maximum flame temperature shifts toward the inlet of the reactants.The results also reveal that by increasing the swirl angle of the flow,the position of the minimum velocity value(opposite to the direction of the axis)tends towards the outlet.The results also indicate that the maximum temperature of the combustion chamber increases with increasing the swirl angle,and inθ=35°,the maximum temperature is 1711℃and inθ=41°,this value is 1812℃.Finally,by increasing the swirl angle toθ=47°,the maximum flame temperature position is found at a considerable distance from the inlet and is 1842℃.
基金CAPES for financial support with the project 117/11
文摘As a support material, zeolite can be used to promote the granulation process due to its high settable property and the ability to retain biomass on its surface. The present paper reports on the influence of zeolite addition on the hydrodynamic behavior of an expanded granular sludge bed reactor(EGSB). Different models were applied to fit the flow pattern and to compare EGSB hydrodynamic performance with and without the addition of zeolite. The experimental data fit the tanks in a series model for zeolite bed height of 5 cm and upflow velocity of 6 m/hr.Higher axial dispersion degree(D/uL) was obtained at lower heights of zeolite. The real hydraulic retention time(HRTr) was increased with both increased zeolite bed height and increased upflow velocity. The short-circuit results for 5 cm of zeolite bed and 6, 8 and 10 m/hr upflow velocity were 0.3, 0.24 and 0.19 respectively, demonstrating the feasibility of using zeolite for a proper hydrodynamic environment to operate the EGSB reactor. The presence of zeolite resulted in the higher percentage values of dead zones, ranging from 12% to 24%.Zeolite addition exerted a positive effect on the hydrodynamics pattern for this technology being advantageous for the anaerobic process because of its possible contribution to better biofilm agglomeration, granule formation and substrate-microorganism contact.