Gases containing sulfur oxides can cause corrosion and failure of bellows used as furnace blowers in high-temperature environments.In order to mitigate this issue,the behavior of an effective blast furnace blower has ...Gases containing sulfur oxides can cause corrosion and failure of bellows used as furnace blowers in high-temperature environments.In order to mitigate this issue,the behavior of an effective blast furnace blower has been examined in detail.Firstly,the Sereda corrosion model has been introduced to simulate the corrosion rate of the related bellows taking into account the effects of temperature and SO_(2) gas;such results have been compared with effective measurements;then,the average gas velocity in the pipeline and the von Mises stress distribution of the inner draft tube have been analyzed using a Fluid-Structure Interaction model.Finally,the semi-closed internal corrosion environment caused by a 5 mm radial gap between the inner draft tube and the bellows has been considered.The gas flow rate in the residential space has been found to be low(0.5 ms–this value leads to a stable semi-closed internal corrosion environment for exhaust gas exchange);water phase in the exhaust gas is prone to accelerate the corrosion rate.On this basis,a bellows with an optimized inner draft tube has proposed,which includes corrosion-resistant honeycomb buffer rings.展开更多
Based on the Naviev-Stokes equations and the standard κ-ε turbulence model, this paper presents the derivation of the governing equations for the turbulent flow field in a draft tube. The mathematical model for the ...Based on the Naviev-Stokes equations and the standard κ-ε turbulence model, this paper presents the derivation of the governing equations for the turbulent flow field in a draft tube. The mathematical model for the turbulent flow through a draft tube is set up when the boundary conditions, including the inlet boundary conditions, the outlet boundary conditions and the wall boundary conditions, have been implemented. The governing equations are formulated in a discrete form on a staggered grid system by the finite volume method. The second-order central difference approximation and hybrid scheme are used for discretization. The computation and analysis on internal flow through a draft tube have been carried out by using the simplee algorithm and cfx-tasc flow software so as to obtain the simulated flow fields. The calculation results at the design operating condition for the draft tube are presented in this paper. Thereby, an effective method for simulating the internal flow field in a draft tube has been explored.展开更多
The application of a new type of moving bed reactor with draft tube for coal gasification was investigated. Successful coal gasification experiments were achieved using the coal gasifier. Product gas containing hydrog...The application of a new type of moving bed reactor with draft tube for coal gasification was investigated. Successful coal gasification experiments were achieved using the coal gasifier. Product gas containing hydrogen as high as 60% was obtained, and the calorific value of the product of 10 MJ·m-3 was obtained using air as oxidant. The reaction temperature of coal gasification in the moving bed was maintained at 870 °C which was comparatively low for coal gasification. Maximum coal gasification efficiency of 92% was obtained.展开更多
The Lattice Boltzmann method （LBM） is used to simulate the flow field in a bifurcate channel which is a simplified model of the draft tube of hydraulic turbine machine. According to the simulation results, some qual...The Lattice Boltzmann method （LBM） is used to simulate the flow field in a bifurcate channel which is a simplified model of the draft tube of hydraulic turbine machine. According to the simulation results, some qualitative conclusions can be deduced. The reason of uneven flux in different branches of draft tube is given. Not only the vortex rope itself, but also the attenuation of the rotation strength is important in bringing on the uneven flux. The later leads to adverse pressure gradient, and changes the velocity profile. If the outlet contains more than one exit, the one that contains the vortex rope will lose flux because of this adverse pressure gradient. Several possible methods can be used to minimize the adverse pressure gradient domain in order to improve the efficiency of turbine machine.展开更多
In this study, the goal is to increase the efficiency of a high-pressure hydraulic turbine. The goal is achieved by numerical flow simulation using CFX-TASCflow. This approach reduces costs and time compared to the ex...In this study, the goal is to increase the efficiency of a high-pressure hydraulic turbine. The goal is achieved by numerical flow simulation using CFX-TASCflow. This approach reduces costs and time compared to the experimental approach and allows for improving the turbine productivity and its design. The analysis of energy losses in the flow part of the turbine Fr500, as well as the analysis of the influence of the opening of the guide vanes on changes in energy losses. The results showed that the greatest losses occur in the guide vane 3.02% based on the two-dimensional model and 2.5% based on the 3D model, which significantly affects the efficiency. The analysis was carried out using programs for calculating fluid flow in two-dimensional and three-dimensional formulations. With the help of the study, the main energy problem is solved—increasing efficiency.展开更多
Draft tube vortex rope is considered a special cavitation flow phenomenon in tubular turbine units.Cavitation vortex rope is one of the most detrimental factors affecting the safety of hydraulic turbines.In this study...Draft tube vortex rope is considered a special cavitation flow phenomenon in tubular turbine units.Cavitation vortex rope is one of the most detrimental factors affecting the safety of hydraulic turbines.In this study,ANSYS CFX software was utilized to numerically simulate the internal cavitation flow of a hydraulic turbine draft tube.The evolution of the cavitation vortex core was characterized by vortex line distribution and vorticity transport equation.The shape and number of blades influenced the revolving direction and distribution characteristics of the vortex close to the runner cone,which formed a counterclockwise-clockwise-counterclockwise distribution pattern.Simultaneously,there were many secondary flows in the draft tube.Mutual cancellation and dissipation between the flows was one of the reasons for reduction in vorticity.When the cross-sectional shape of the draft tube was changed,the vorticity was distributed from the center of the vortex rope to all parts of the cross-sectional draft tube,with extreme values at the center and at the walls.The vortex stretching and dilatation terms played a major role in the change in vorticity,with the baroclinic torque having an effect at the center of the vortex rope,this study is helpful to understand the flow of water in the draft tube and guide the design and optimization of the draft tube in engineering application.展开更多
Open-sided draft tubes provide an optimal gas distribution through a cross flow pattern between the spout and the annulus in conical spouted beds.The design,optimization,control,and scale-up of the spouted beds requir...Open-sided draft tubes provide an optimal gas distribution through a cross flow pattern between the spout and the annulus in conical spouted beds.The design,optimization,control,and scale-up of the spouted beds require precise information on operating and peak pressure drops.In this study,a multi-layer perceptron(MLP)neural network was employed for accurate prediction of these hydrodynamic characteristics.A relatively huge number of experiments were accomplished and the most influential dimensionless groups were extracted using the Buckingham-pi theorem.Then,the dimensionless groups were used for developing the MLP model for simultaneous estimation of operating and peak pressure drops.The iterative constructive technique confirmed that 4-14-2 is the best structure for the MLP model in terms of absolute average relative deviation(AARD%),mean square error(MSE),and regression coefficient(R^(2)).The developed MLP approach has an excellent capacity to predict the transformed operating(MSE=0.00039,AARD%=1.30,and R^(2)=0.76099)and peak(MSE=0.22933,AARD%=11.88,and R2=0.89867)pressure drops.展开更多
The three-dimensional unsteady turbulent flow is studied numerically in the whole flow passage of hydraulic turbine, and vortex flow in the draft tube is predicted accurately in this paper. The numerical prediction is...The three-dimensional unsteady turbulent flow is studied numerically in the whole flow passage of hydraulic turbine, and vortex flow in the draft tube is predicted accurately in this paper. The numerical prediction is based on the Navier-Stokes equations and Large-Eddy Simulation （LES） model. The SIMPLE algorithm with the body fitted coordinate and tetrahedroid grid system is applied for the solution of the discretization governing equations.展开更多
A new Reynolds-averaged Navier-Stokes （RANS） turbulence model is developed in order to correctly predict the mean flow field in a draft tube operating under partial load using 2-D axisymmetric simulations. It is sho...A new Reynolds-averaged Navier-Stokes （RANS） turbulence model is developed in order to correctly predict the mean flow field in a draft tube operating under partial load using 2-D axisymmetric simulations. It is shown that although 2-D axisymmetric simulations cannot model the 3-D unsteady features of the vortex rope, they can give the average location of the vortex rope in the draft tube. Nevertheless, RANS simulations underpredict the turbulent kinetic energy （TKE） production and diffusion near the center of the draft tube where the vortex rope forms, resulting in incorrect calculation of TKE profiles and, hence, poor prediction of the axial velocity. Based on this observation, a new k- c turbulence RANS model taking into account the extra production and diffusion of TKE due to coherent structures associated with the vortex rope formation is developed. The new model can successfully predict the mean flow velocity with significant improvements in comparison with the realizable k - c model. This is attributed to better prediction of TKE production and diffusion by the new model in the draft tube under partial load. Specifically, the new model calculates 31% more production and 46% more diffusion right at the shear layer when compared to the k - ~ model.展开更多
Draft tube vortex is one of the main causes of hydraulic instability in hydraulic reaction turbines,in particular Francis turbines.A method of cavitation calculations was proposed to predict the pressure fluctuations ...Draft tube vortex is one of the main causes of hydraulic instability in hydraulic reaction turbines,in particular Francis turbines.A method of cavitation calculations was proposed to predict the pressure fluctuations induced by draft tube vortices in a model Francis turbine,by solving RANS equations with RNG k-turbulence model and ZGB cavitation model,with modified turbulence viscosity.Three cases with different flow rates at high head were studied.In the study case of part load,two modes of revolutions with the same rotating direction,revolution around the axis of the draft tube cone,and revolution around the core of the vortex rope,can be recognized.The elliptical shaped vortex rope causes anisotropic characteristics of pressure fluctuations around the centerline of the draft tube cone.By analyzing the phase angles of the pressure fluctuations,the role of the vortex rope as an exciter in the oscillating case can be recognized.An analysis of Batchelor instability,i.e.instability in q-vortex like flow structure,has been carried out on the draft tube vortices in these three cases.It can be concluded that the trajectory for study case with part load lies in the region of absolute instability(AI),and it lies in the region of convective instability(CI)for study case with design flow rate.Trajectory for study case with over load lies in the AI region at the inlet of the draft tube,and enters CI region near the end of the elbow.展开更多
In terms of gas holdup,liquid velocity,and volumetric mass transfer coefficient for oxygen(KLa),the hydrodynamic behavior of four configurations of an airlift reactor(ALR)with a net draft tube(NDT)of different net mes...In terms of gas holdup,liquid velocity,and volumetric mass transfer coefficient for oxygen(KLa),the hydrodynamic behavior of four configurations of an airlift reactor(ALR)with a net draft tube(NDT)of different net mesh sizes(ALR-NDT-3,6,12,and ALR)have been numerically simulated for a range of inlet air flow rates.The effect of various levels of ratio of height(H)to inner tube diameter(D)of the net draft tube(H/D:9.3,10.7,17.5,and 20)and ratio of inner cross-sectional area of the riser(Ar)to the inner cross sectional area of the downcomer(Ad)(Ad/Ar:1.3 and 7)for different air flow rates is also evaluated for each reactor configuration operating with an air-water system.The two-fluid formulation coupled with the k-εturbulence model is used for computational fluid dynamics(CFD)analysis of flow with Eulerian descriptions for the gas and liquid phases.Interactions between air bubbles and liquid are taken into account using momentum exchange and drag coefficient based on two different correlations.Trends in the predicted dynamical behavior are similar to those found experimentally.A good agreement was achieved suggesting that geometric effects are properly accounted for by the CFD model.After a comparison with experimental data,numerical simulations show significant enhanced gas holdup,liquid velocity,and Kta for the ALR-NDTs compared with the conventional ALR.Higher gas holdup values are achieved for ALR-NDT-3 than that for the other ALRs because it acts like a bubble column reactor as the holes present in the NDT are large.Maximum liquid velocities are seen in ALR-NDT-12,which operates like a conventional ALR.Moreover,the interaction between the NDT and upward gas flow leads to cross flow through the net,small bubbles,and high interfacial area as well as good mass transfer.This was significant in ALR-NDT-6 with maximum Kta value of 0.031 s-1.The applied methodology provides an insightful understanding of the complex dynamic behavior of ALR-NDTs and may be helpful in optimizing the design and scale-up of reactors.展开更多
Numerical simulations of the flow in the draft tube of a Francis turbine are carried out in order to elucidate the effects of tangential velocity on flow stability.Influence of the location of the maximum tangential v...Numerical simulations of the flow in the draft tube of a Francis turbine are carried out in order to elucidate the effects of tangential velocity on flow stability.Influence of the location of the maximum tangential velocity is explored considering the equality of the total energy at the inlet of the draft tube.It is found that the amplitude of the pressure fluctuation decreases when the location of the maximum of the tangential velocity moves from the centre to the wall on the cross section.Thus,the stability of the flow in the draft tube increases with the moving of the location of the maximum tangential velocity.However,the relative hydraulic loss increases and the recovery coefficient of the draft tube decreases slightly.展开更多
Experiment and simulation were used to study the flow fields of a liquid-solid-solid three-phase system in a draft-tube stirred reactor with a six-flat-bladed turbine impeller(BT)and a 45°pitched six-bladed upflo...Experiment and simulation were used to study the flow fields of a liquid-solid-solid three-phase system in a draft-tube stirred reactor with a six-flat-bladed turbine impeller(BT)and a 45°pitched six-bladed upflow turbine impeller(PBTU45).The computational fluid dynamics(CFD)formulation was based on a 3D Eulerian multi-fluid model along with a renormalization group(RNG)k-ε turbulence model,which took into account the inter-phase momentum exchange between different phases.The CFD model was validated using experimental data,and the suspension quality was validated by determining the standard deviation of the solid concentration.Good solid suspension was achieved in flow fields agitated by the BT impeller at low impeller speeds.The draft tube adversely affected solid dispersion at most impeller speeds.In flow fields agitated by the PBTU45 impeller,good solid suspension required a faster impeller speed.The suspension quality with the draft tube was better than that without the draft tube under most operating conditions.The power consumption of the BT or PBTU45 impeller with the draft tube was less than that without the draft tube at most impeller speeds.展开更多
基金funded by Science and Technology Project of Hebei Education Department(Project No.QN2022198).
文摘Gases containing sulfur oxides can cause corrosion and failure of bellows used as furnace blowers in high-temperature environments.In order to mitigate this issue,the behavior of an effective blast furnace blower has been examined in detail.Firstly,the Sereda corrosion model has been introduced to simulate the corrosion rate of the related bellows taking into account the effects of temperature and SO_(2) gas;such results have been compared with effective measurements;then,the average gas velocity in the pipeline and the von Mises stress distribution of the inner draft tube have been analyzed using a Fluid-Structure Interaction model.Finally,the semi-closed internal corrosion environment caused by a 5 mm radial gap between the inner draft tube and the bellows has been considered.The gas flow rate in the residential space has been found to be low(0.5 ms–this value leads to a stable semi-closed internal corrosion environment for exhaust gas exchange);water phase in the exhaust gas is prone to accelerate the corrosion rate.On this basis,a bellows with an optimized inner draft tube has proposed,which includes corrosion-resistant honeycomb buffer rings.
基金Supported by the National Natural Science Foundation of China(10162002) the Key Project of Chinese Ministry Education (204138) the Sci-ence Foundation of Yunnan Education Bureau(5Y0020A)
文摘Based on the Naviev-Stokes equations and the standard κ-ε turbulence model, this paper presents the derivation of the governing equations for the turbulent flow field in a draft tube. The mathematical model for the turbulent flow through a draft tube is set up when the boundary conditions, including the inlet boundary conditions, the outlet boundary conditions and the wall boundary conditions, have been implemented. The governing equations are formulated in a discrete form on a staggered grid system by the finite volume method. The second-order central difference approximation and hybrid scheme are used for discretization. The computation and analysis on internal flow through a draft tube have been carried out by using the simplee algorithm and cfx-tasc flow software so as to obtain the simulated flow fields. The calculation results at the design operating condition for the draft tube are presented in this paper. Thereby, an effective method for simulating the internal flow field in a draft tube has been explored.
文摘The application of a new type of moving bed reactor with draft tube for coal gasification was investigated. Successful coal gasification experiments were achieved using the coal gasifier. Product gas containing hydrogen as high as 60% was obtained, and the calorific value of the product of 10 MJ·m-3 was obtained using air as oxidant. The reaction temperature of coal gasification in the moving bed was maintained at 870 °C which was comparatively low for coal gasification. Maximum coal gasification efficiency of 92% was obtained.
基金supported by the Key Project of National Natural Science Foundation of China (10532010)
文摘The Lattice Boltzmann method （LBM） is used to simulate the flow field in a bifurcate channel which is a simplified model of the draft tube of hydraulic turbine machine. According to the simulation results, some qualitative conclusions can be deduced. The reason of uneven flux in different branches of draft tube is given. Not only the vortex rope itself, but also the attenuation of the rotation strength is important in bringing on the uneven flux. The later leads to adverse pressure gradient, and changes the velocity profile. If the outlet contains more than one exit, the one that contains the vortex rope will lose flux because of this adverse pressure gradient. Several possible methods can be used to minimize the adverse pressure gradient domain in order to improve the efficiency of turbine machine.
文摘In this study, the goal is to increase the efficiency of a high-pressure hydraulic turbine. The goal is achieved by numerical flow simulation using CFX-TASCflow. This approach reduces costs and time compared to the experimental approach and allows for improving the turbine productivity and its design. The analysis of energy losses in the flow part of the turbine Fr500, as well as the analysis of the influence of the opening of the guide vanes on changes in energy losses. The results showed that the greatest losses occur in the guide vane 3.02% based on the two-dimensional model and 2.5% based on the 3D model, which significantly affects the efficiency. The analysis was carried out using programs for calculating fluid flow in two-dimensional and three-dimensional formulations. With the help of the study, the main energy problem is solved—increasing efficiency.
基金the National Natural Science Foundation,China(Grant No.52079118)Key Research and Development Plan of Sichuan Provincial Department of Science and Technology(Grant No.2023YFQ0021)+1 种基金Qinghai Province“Kunlun Talents High-end Innovation and Entrepreneurship Talent Program”Qinghai University of Science and Technology talent introduction of scientific research special grants,Central leading local(scientific and technological innovation base construction)project XZ202201YD0017CJiangsu South-North Water Diversion Science and Technology R&D Project(Grant No.JSNSBD202303).
文摘Draft tube vortex rope is considered a special cavitation flow phenomenon in tubular turbine units.Cavitation vortex rope is one of the most detrimental factors affecting the safety of hydraulic turbines.In this study,ANSYS CFX software was utilized to numerically simulate the internal cavitation flow of a hydraulic turbine draft tube.The evolution of the cavitation vortex core was characterized by vortex line distribution and vorticity transport equation.The shape and number of blades influenced the revolving direction and distribution characteristics of the vortex close to the runner cone,which formed a counterclockwise-clockwise-counterclockwise distribution pattern.Simultaneously,there were many secondary flows in the draft tube.Mutual cancellation and dissipation between the flows was one of the reasons for reduction in vorticity.When the cross-sectional shape of the draft tube was changed,the vorticity was distributed from the center of the vortex rope to all parts of the cross-sectional draft tube,with extreme values at the center and at the walls.The vortex stretching and dilatation terms played a major role in the change in vorticity,with the baroclinic torque having an effect at the center of the vortex rope,this study is helpful to understand the flow of water in the draft tube and guide the design and optimization of the draft tube in engineering application.
文摘Open-sided draft tubes provide an optimal gas distribution through a cross flow pattern between the spout and the annulus in conical spouted beds.The design,optimization,control,and scale-up of the spouted beds require precise information on operating and peak pressure drops.In this study,a multi-layer perceptron(MLP)neural network was employed for accurate prediction of these hydrodynamic characteristics.A relatively huge number of experiments were accomplished and the most influential dimensionless groups were extracted using the Buckingham-pi theorem.Then,the dimensionless groups were used for developing the MLP model for simultaneous estimation of operating and peak pressure drops.The iterative constructive technique confirmed that 4-14-2 is the best structure for the MLP model in terms of absolute average relative deviation(AARD%),mean square error(MSE),and regression coefficient(R^(2)).The developed MLP approach has an excellent capacity to predict the transformed operating(MSE=0.00039,AARD%=1.30,and R^(2)=0.76099)and peak(MSE=0.22933,AARD%=11.88,and R2=0.89867)pressure drops.
基金Project supported by the National Natural Science Foundation of China (Grant No :50179021) and the Youth Scienceand Technology Foundation of Sichuan (Grant No :05ZQ026-07) .
文摘The three-dimensional unsteady turbulent flow is studied numerically in the whole flow passage of hydraulic turbine, and vortex flow in the draft tube is predicted accurately in this paper. The numerical prediction is based on the Navier-Stokes equations and Large-Eddy Simulation （LES） model. The SIMPLE algorithm with the body fitted coordinate and tetrahedroid grid system is applied for the solution of the discretization governing equations.
基金funded in part by the Office of Energy Efficiency and Renewable Energy (EERE), U.S. Department of Energy, under Award Numbers DE-EE0002667 (the DOE/PSU Graduate Student Fellowship Program for Hydropower Research)DE-EE0002668 (The HRF Fellowship)the Hydro Research Foundation
文摘A new Reynolds-averaged Navier-Stokes （RANS） turbulence model is developed in order to correctly predict the mean flow field in a draft tube operating under partial load using 2-D axisymmetric simulations. It is shown that although 2-D axisymmetric simulations cannot model the 3-D unsteady features of the vortex rope, they can give the average location of the vortex rope in the draft tube. Nevertheless, RANS simulations underpredict the turbulent kinetic energy （TKE） production and diffusion near the center of the draft tube where the vortex rope forms, resulting in incorrect calculation of TKE profiles and, hence, poor prediction of the axial velocity. Based on this observation, a new k- c turbulence RANS model taking into account the extra production and diffusion of TKE due to coherent structures associated with the vortex rope formation is developed. The new model can successfully predict the mean flow velocity with significant improvements in comparison with the realizable k - c model. This is attributed to better prediction of TKE production and diffusion by the new model in the draft tube under partial load. Specifically, the new model calculates 31% more production and 46% more diffusion right at the shear layer when compared to the k - ~ model.
基金supported by the National Natural Science Foundation of China(Grant No.51076077)National Key Technology R&D Program of China(Grant No.2008BAC48B02)
文摘Draft tube vortex is one of the main causes of hydraulic instability in hydraulic reaction turbines,in particular Francis turbines.A method of cavitation calculations was proposed to predict the pressure fluctuations induced by draft tube vortices in a model Francis turbine,by solving RANS equations with RNG k-turbulence model and ZGB cavitation model,with modified turbulence viscosity.Three cases with different flow rates at high head were studied.In the study case of part load,two modes of revolutions with the same rotating direction,revolution around the axis of the draft tube cone,and revolution around the core of the vortex rope,can be recognized.The elliptical shaped vortex rope causes anisotropic characteristics of pressure fluctuations around the centerline of the draft tube cone.By analyzing the phase angles of the pressure fluctuations,the role of the vortex rope as an exciter in the oscillating case can be recognized.An analysis of Batchelor instability,i.e.instability in q-vortex like flow structure,has been carried out on the draft tube vortices in these three cases.It can be concluded that the trajectory for study case with part load lies in the region of absolute instability(AI),and it lies in the region of convective instability(CI)for study case with design flow rate.Trajectory for study case with over load lies in the AI region at the inlet of the draft tube,and enters CI region near the end of the elbow.
文摘In terms of gas holdup,liquid velocity,and volumetric mass transfer coefficient for oxygen(KLa),the hydrodynamic behavior of four configurations of an airlift reactor(ALR)with a net draft tube(NDT)of different net mesh sizes(ALR-NDT-3,6,12,and ALR)have been numerically simulated for a range of inlet air flow rates.The effect of various levels of ratio of height(H)to inner tube diameter(D)of the net draft tube(H/D:9.3,10.7,17.5,and 20)and ratio of inner cross-sectional area of the riser(Ar)to the inner cross sectional area of the downcomer(Ad)(Ad/Ar:1.3 and 7)for different air flow rates is also evaluated for each reactor configuration operating with an air-water system.The two-fluid formulation coupled with the k-εturbulence model is used for computational fluid dynamics(CFD)analysis of flow with Eulerian descriptions for the gas and liquid phases.Interactions between air bubbles and liquid are taken into account using momentum exchange and drag coefficient based on two different correlations.Trends in the predicted dynamical behavior are similar to those found experimentally.A good agreement was achieved suggesting that geometric effects are properly accounted for by the CFD model.After a comparison with experimental data,numerical simulations show significant enhanced gas holdup,liquid velocity,and Kta for the ALR-NDTs compared with the conventional ALR.Higher gas holdup values are achieved for ALR-NDT-3 than that for the other ALRs because it acts like a bubble column reactor as the holes present in the NDT are large.Maximum liquid velocities are seen in ALR-NDT-12,which operates like a conventional ALR.Moreover,the interaction between the NDT and upward gas flow leads to cross flow through the net,small bubbles,and high interfacial area as well as good mass transfer.This was significant in ALR-NDT-6 with maximum Kta value of 0.031 s-1.The applied methodology provides an insightful understanding of the complex dynamic behavior of ALR-NDTs and may be helpful in optimizing the design and scale-up of reactors.
基金supported by the open fund of State Key Laboratory of Hydroscience and Engineer of Tsinghua University(No.sklhse-2013-E-02)the Special Major Project of Science and Technology of Zhejiang province(No.2013C 01139)
文摘Numerical simulations of the flow in the draft tube of a Francis turbine are carried out in order to elucidate the effects of tangential velocity on flow stability.Influence of the location of the maximum tangential velocity is explored considering the equality of the total energy at the inlet of the draft tube.It is found that the amplitude of the pressure fluctuation decreases when the location of the maximum of the tangential velocity moves from the centre to the wall on the cross section.Thus,the stability of the flow in the draft tube increases with the moving of the location of the maximum tangential velocity.However,the relative hydraulic loss increases and the recovery coefficient of the draft tube decreases slightly.
文摘Experiment and simulation were used to study the flow fields of a liquid-solid-solid three-phase system in a draft-tube stirred reactor with a six-flat-bladed turbine impeller(BT)and a 45°pitched six-bladed upflow turbine impeller(PBTU45).The computational fluid dynamics(CFD)formulation was based on a 3D Eulerian multi-fluid model along with a renormalization group(RNG)k-ε turbulence model,which took into account the inter-phase momentum exchange between different phases.The CFD model was validated using experimental data,and the suspension quality was validated by determining the standard deviation of the solid concentration.Good solid suspension was achieved in flow fields agitated by the BT impeller at low impeller speeds.The draft tube adversely affected solid dispersion at most impeller speeds.In flow fields agitated by the PBTU45 impeller,good solid suspension required a faster impeller speed.The suspension quality with the draft tube was better than that without the draft tube under most operating conditions.The power consumption of the BT or PBTU45 impeller with the draft tube was less than that without the draft tube at most impeller speeds.
