The gas-liquid-solid three-phase mixed flow is the most general in multiphase mixed transportation. It is significant to exactly solve the coupling hydraulic transient problems of this type of multiphase mixed flow in...The gas-liquid-solid three-phase mixed flow is the most general in multiphase mixed transportation. It is significant to exactly solve the coupling hydraulic transient problems of this type of multiphase mixed flow in pipelines. Presently, the method of characteristics is widely used to solve classical hydraulic transient problems. However, when it is used to solve coupling hydraulic transient problems, excessive interpolation errors may be introduced into the results due to unavoidable multiwave interpolated calculations. To deal with the problem, a finite difference scheme based on the Steger- Warming flux vector splitting is proposed. A flux vector splitting scheme is established for the coupling hydraulic transient model of gas-liquid-solid three-phase mixed flow in the pipelines. The flux subvectors are then discretized by the Lax-Wendroff central difference scheme and the Warming-Beam upwind difference scheme with second-order precision in both time and space. Under the Rankine-Hugoniot conditions and the corresponding boundary conditions, an effective solution to those points located at the boundaries is developed, which can avoid the problem beyond the calculation region directly induced by the second-order discrete technique. Numerical and experimental verifications indicate that the proposed scheme has several desirable advantages including high calculation precision, excellent shock wave capture capability without false numerical oscillation, low sensitivity to the Courant number, and good stability.展开更多
The computational fluid dynamics （CFD）-population balance equations （PBE） coupled model is employed to investigate the hydrodynamics in a gas-slurry internal loop reactor with external slurry circulation. The pred...The computational fluid dynamics （CFD）-population balance equations （PBE） coupled model is employed to investigate the hydrodynamics in a gas-slurry internal loop reactor with external slurry circulation. The predicted radial profiles of local gas holdup and bubble diameter are in good agreement with the corresponding experimental data. The spatio-temporal velocity profile of the gas phase reveals that the upward movement of gas is slowed down and the residence time of gas is prolonged by the downward momentum of the slurry, introduction of the external slurry can greatly improve the uniformity of gas holdup distribution in the reactor, especially in the downcomer-tube action region. Moreover, the interaction between the downward slurry and upward gas can lead to small bubble size and high interfacial area as well as good mass and heat transfer. The above results suggest the function of external slurry circulation for the internal loop reactor and would be helpful for optimizing the design and scale up of reactors.展开更多
The local gas-phase flow characteristics such as local gas holdup(εg), local bubble velocity (V_b) and local bubble mean diameter(d_b) at a specified point in a gas-liquid-solid three-phase reversedflow jet loop reac...The local gas-phase flow characteristics such as local gas holdup(εg), local bubble velocity (V_b) and local bubble mean diameter(d_b) at a specified point in a gas-liquid-solid three-phase reversedflow jet loop reactor was experimentally investigated by a five-pointconductivity probe. The effects of gas jet flow rate, liquid jet flowrate, solid loading, nozzle diameter and axial position on the localεg, V_b and d_b profiles were discussed. The presence of solids atlow solid concentrations not only increased the local εg and V_b,but also decreased the local d_b. The optimum solid loading for themaximum local εg and V_b together with the minimum local d_b was0.16×10^-3 m^3, corresponding to a solid volume fraction ε_S＝2.5/100.展开更多
The parallel-competing iodide-iodate reaction scheme was used to study the micromixing performance in a multi-phase stirred tank of 0.3 m diameter.The impeller combination consisted of a half elliptical blade disk tur...The parallel-competing iodide-iodate reaction scheme was used to study the micromixing performance in a multi-phase stirred tank of 0.3 m diameter.The impeller combination consisted of a half elliptical blade disk turbine below two down-pimping wide-blade hydrofoils,identified as HEDT + 2WH_D.Nitrogen and glass beads of100 μm diameter and density 2500 kg-m^(-3) were used as the dispersed phases.The micromixing could be improved by sparging gas because of its additional potential energy.Also,micromixing could be improved by the solid particles with high kinetic energy near the impeller tip.In a gas-solid-liquid system,the gas-liquid film vibration with damping,due to the frequent collisions between the bubbles and particles,led to the decrease of the turbulence level in the liquid and caused eventually the deterioration of the micromixing.A Damping Film Dissipation model is formulated to shed light on the above micromixing performances.At last,the micromixing time t_m according to the incorporation model varied from 1.9 ms to 6.7 ms in our experiments.展开更多
The multiphase flow characteristic is one of the most concerning problems during solid fluidization exploitation of marine natural gas hydrate reservoirs.In this research,a new transient gas-liquid-solid multiphase fl...The multiphase flow characteristic is one of the most concerning problems during solid fluidization exploitation of marine natural gas hydrate reservoirs.In this research,a new transient gas-liquid-solid multiphase flow model with hydrate phase transition was developed.Meanwhile,this model considered the coupling relationship among convective heat transfer,hydrate dynamic decomposition,and multi-phase flow.The model can simulate the change of flow pattern from solid-liquid to gas-liquid-solid flow,and describe the distribution character of volume fraction of phase,wellbore temperature and pressure,and hydrate decomposition rate during transportation.The simulation results indicate that the hydrate decomposition region in the wellbore gradually expands,but the hydrate decomposition rate gradually decreases during the solid fluidization exploitation of hydrate.When mining time lasts for 4 h,and the bottom hole pressure decreases by about 0.4 MPa.Increasing NaCl concentration in seawater helps expand hydrate decomposition regions and improves the wellbore hydrate decomposition rate.When the Nacl mass fraction in seawater reaches 15%,it will raise the hydrate decomposition regions to the whole wellbore.In addition,the higher the wellhead backpressure,the lower the decomposition area and decomposition rate of hydrate in the wellbore.When wellhead backpressure reaches 2 MPa,the volume fraction of gas near the wellhead will reduce to about 12%.This work is expected to provide a theoretical basis for the development of marine hydrate reservoirs.展开更多
The effects of liquid viscosities, solid circulating rates, liquid and gas velocities and phase holdups on the axial dispersion coefficient, Dax, were investigated in a gas-liquid-solid circulating fluidized bed (GLSC...The effects of liquid viscosities, solid circulating rates, liquid and gas velocities and phase holdups on the axial dispersion coefficient, Dax, were investigated in a gas-liquid-solid circulating fluidized bed (GLSCFB).Liquid viscosity promotes the axial liquid backmixing when solid particles and gas bubbles are present. Increases in gas velocities and solid circulating rates lead to higher Dax. The effects of liquid velocity on Dax are associated with liquid viscosity. Compared with conventional expanded beds, the GLSCFBs hold less axial liquid dispersion,approaching ideal plug-flow reactors.展开更多
Gas-liquid-solid three-phase flow is common in various fields,making it crucial to accurately and efficiently describe its dynamic behaviors.To better perform the gas-liquid-solid three-phase simulations,a coupling co...Gas-liquid-solid three-phase flow is common in various fields,making it crucial to accurately and efficiently describe its dynamic behaviors.To better perform the gas-liquid-solid three-phase simulations,a coupling code based on GPU named as CoSim-FVDEM is developed,which combines the finite volume method(FVM)and the discrete element method(DEM).This code encompasses unresolved,resolved and resolved-unresolved coupling methods,making it suitable for three-phase flow simulations involving solid particles of various sizes.A series of cases are conducted to validate the accuracy of the developed coupling algorithm,including complex dam breach flow,water entry test of a single sphere and multi-sphere within rotating roller.Finally,a gas-liquid-solid three-phase flow numerical experiment is performed,which involves the bi-disperse granular systems in a rotating roller.Base on the numerical results,the dynamic behaviors of the three-phase flow are analyzed and the computational efficiency is evaluated.The results indicate that the developed coupling code can better be used for the dynamic analysis of large-scale gas-liquid-solid three-phase flow.展开更多
Gas-liquid-solid mini-fluidized beds known for high efficiency with controllable mass and heat transfer characteristics,have good application prospects in fields such as multiphase reaction process enhancement and int...Gas-liquid-solid mini-fluidized beds known for high efficiency with controllable mass and heat transfer characteristics,have good application prospects in fields such as multiphase reaction process enhancement and intrinsic kinetic detection.For three-phase mini-flow systems,the bed wall has a significant impact on spatiotemporal distribution of multi-phase flow structure,which influence the motion state of dispersed phase,make predicted phase holdup and residence time deviate from experimental values.However,current research on the quantitative impact of bed walls on flow structures is still limited,which hinders the optimization design and industrial application of such reactors.In this work,a meso-scale flow model of gas-liquid-solid mini-fluidized beds considering macro-scale effects between bed wall and flow is developed based on the principle of meso-scale science and introducing semi-theoretical formulas that take the effects of bed walls on particles and bubbles into account.The calculated values of this model are in good agreement with experimental data,where prediction of phase holdup fits well with experimental results,the deviation of bubble size and terminal velocity are within 10%.Compared to existing models,this model demonstrates a higher level of accuracy in predicting the flow patterns of mini-fluidized beds,particularly those with pronounced wall effect.This research has laid a foundation for the design,scale-up and industrial application of mini-fluidized bed reactors.展开更多
Gas-liquid-solid circulating fluidized bed(GLSCFB)is an important type of chemical reactor.The complex mesoscale flow structure of GLSCFB was described through the mesoscale flow structure parameters based on the ener...Gas-liquid-solid circulating fluidized bed(GLSCFB)is an important type of chemical reactor.The complex mesoscale flow structure of GLSCFB was described through the mesoscale flow structure parameters based on the energy-minimization multi-scale(EMMS)model.The liquid-solid drag force model(Drag-ls model)was proposed and it was found that the drag coefficient between liquid and solid in three-phase systems increased compared to liquid-solid two-phase systems because of the influence of gas phase.The gas-solid drag force model(Drag-gs model)was proposed based on a modified unified wake model.Furthermore,the combination of EMMS model and computational fluid dynamics(CFD)in GLSCFB was implemented,and the dynamic evolution process of particle clusters and distributions of gas holdup and solid holdup in GLSCFB were simulated more accurately by the models.The simulation results indicate that the drag forces exerted on the solid phase by both the liquid and gas phases are coupled and mutually influence each other.The simulated values of solid holdup may deviate from the experimental values if the interactions between the gas-solid and liquid-solid phases are corrected independently.When the average solid holdup of the bed is low,the mesoscale phenomena such as particle aggregation are not obvious.As the solid holdup increases,there is a significant phenomenon of particle aggregation in the bed.The particles undergo a spatiotemporal evolution process of forming elongated clusters with high solid holdup,spherical clusters with high solid holdup,and clusters with low solid holdup which has large surface areas.展开更多
The gas-liquid-solid mini fluidized bed(GLSMFB)combines the advantages of fluidized bed and micro-reactor,and meets the requirements for safety and efficiency of green development of process industry.However,there are...The gas-liquid-solid mini fluidized bed(GLSMFB)combines the advantages of fluidized bed and micro-reactor,and meets the requirements for safety and efficiency of green development of process industry.However,there are few studies on its flow performance and no studies on its mass and heat transfer performance.In this paper,the characteristics of gas-liquid mass transfer in a GLSMFB were studied in order to provide basic guidance for the study of GLSMFB reaction performance and application.Using CO_(2)absorption by NaOH as the model process,the gas-liquid mass transfer performance of GLSMFB was investigated.The results show that the liquid volumetric mass transfer coefficient and the gas-liquid interfacial area both increase with the increase of the superficial gas velocity within the experimental parameter range under the same given superficial liquid velocity.At the same ratio of superficial gas to liquid velocity,the liquid volumetric mass transfer coefficient increases with the increase of the super-ficial liquid velocity.Fluidized solid particles strengthen the liquid mass transfer process,and the liquid volumetric mass transfer coefficient is about 13%higher than that of gas-liquid mini bubble column.展开更多
The solid holdup,in a 150 mm-ID×2460 mm-height gas-liquid-solid expanded bed with air,water and glass beads(the diameter of particles is 0.6-0.8 mm)was firstly investigated based on the immersion-type online mult...The solid holdup,in a 150 mm-ID×2460 mm-height gas-liquid-solid expanded bed with air,water and glass beads(the diameter of particles is 0.6-0.8 mm)was firstly investigated based on the immersion-type online multiphase measuring instrument,and bubble behavior was studied via the BVW-2 double electrical conductivity probe.The effect of the superficial gas velocity and liquid velocity on the expanded ratio,the transition ratio,the bubble rising velocity,the gas holdup and the solid holdup was studied.It is discovered that compared with the gas velocity,the liquid velocity has stronger impact on the expanded ratio,but it is opposite for the transition ratio.The average gas holdup and solid holdup increase linearly as the superficial gas velocity goes up.Among it,the gas holdup increases greater in the center,while the solid holdup increases greater near the wall.Compared with it,when the superficial liquid velocity rises,the average gas holdup hardly changes,but the average solid holdup keeps decreasing,especially the solid holdup distributes flatter with the increase of the superficial liquid velocity.展开更多
The hydrodynamics of a gas-liquid-solid fluidized bed was investigated by applying the S statistics method to pressure fluctuations measured under various operating conditions in a laboratory-scale bed. S statistics t...The hydrodynamics of a gas-liquid-solid fluidized bed was investigated by applying the S statistics method to pressure fluctuations measured under various operating conditions in a laboratory-scale bed. S statistics tests reveal the existence of three transition velocities, especially at low gas velocities. Four distinct fluidization regimes, namely, the compacted bed, agitated bed and coalesced and discrete bubble regimes were detected. A comparison of reconstructed attractors of pressure fluctuations measured at different axial positions along the riser and with various solid loadings showed significant differences in the signals compared before fluidization, especially at minimum liquid agitation velocity. Close to the minimum liquid fluidization velocity and high liquid velocities, the variation in particle size has an insignificant effect on the bed hydrodynamics. Therefore, S statistics is a reliable method to demar- cate different fluidization regimes and to characterize the influence of various operating conditions on the hydrodynamics of gas-liquid-solid fluidized beds. The method is applicable in large-scale industrial installations to detect dynamic changes within a bed, such as regime transitions or agglomeration.展开更多
This study proposes a novel cyclone separator with a conical inner core to enhance particle classification efficiency in oil and gas wellhead-recovered liquids.Particle motion and force dynamics are analyzed to optimi...This study proposes a novel cyclone separator with a conical inner core to enhance particle classification efficiency in oil and gas wellhead-recovered liquids.Particle motion and force dynamics are analyzed to optimize key structural parameters,including inlet diameter(D_i),overflow pipe diameter(D_(e)),insertion depth(L_(e)),and bottom flow pipe diameter(D_(z)).Numerical simulations employ the Reynolds stress turbulence model,SIMPLEC algorithm,and discrete phase model to evaluate separation performance in a gas-liquid two-phase system.Results indicate that a smaller D_i improves fine particle separation but increases turbulence;an optimal range of D_i/D_(c)=0.35-0.4 is recommended.Larger D_(e) enhances the diversion ratio,aiding fine particle discharge(D_(e)/D_(c)=0.25-0.35).Increased Le facilitates fine particle overflow but induces vortices,whereas a smaller L_(e) stabilizes the bottom flow for larger particle separation(L_(e)/D_(c)=0.5-0.75).A reduced D_(z) enhances centrifugal force and separation efficiency but may cause turbulence;an optimal D_(z)/D_(c) of 0.6-0.65 is suggested for stability.These findings provide valuable design guidelines for improving cyclone separator performance in multiphase flow applications.展开更多
A numerical method is presented to simulate bubble–particle interaction phenomena in particle-laden flows.The bubble surface is represented in an Eulerian framework by a volume-of-fluid(VOF)method,while particle moti...A numerical method is presented to simulate bubble–particle interaction phenomena in particle-laden flows.The bubble surface is represented in an Eulerian framework by a volume-of-fluid(VOF)method,while particle motions are predicted in a Lagrangian framework.Different frameworks for describing bubble surfaces and particles make it difficult to predict the exact locations of collisions between bubbles and particles.An effective bubble,defined as having a larger diameter than the actual bubble represented by the VOFmethod,is introduced to predict the collision locations.Once the collision locations are determined,the attachment of particles to the bubble surface is determined using a novel numerical algorithm based on collision/induction times.The proposed numerical method is validated through simulations of a rising bubble moving through a layer of particles.The validity of the collision detection algorithm is examined by comparing the collision probability predicted by the present numerical method with that predicted from a theoretical relationship based on bubble/particle diameters.The attachment probability predicted by the present algorithm is found to agree well with that of an experiment.展开更多
Sludge granulation and the effect of gas-liquid-solid separator （GLSS） design on the efficiency of upflow anaerobic sludge blanket （UASB） and upflow anaerobic sludge filter （UASF） reactors, operating at HRTs ran...Sludge granulation and the effect of gas-liquid-solid separator （GLSS） design on the efficiency of upflow anaerobic sludge blanket （UASB） and upflow anaerobic sludge filter （UASF） reactors, operating at HRTs ranging from 3 to 12 h was investigated. VSS/TS ratio gradually increased in both the reactors with increasing sludge age （from 0.5 to more than 0.7 for UASB reactor and 0.012 to 0.043 for UASF reactor）. X-Ray diffraction analysis of the UASF sludge showed the presence of expanding clays revealing its additional absorption capability. Fuoraphyllite and albite precipitation related to excellular polymers of the microbial shell structure, showed the extended growth of microorganisms during sludge granulation. A gradual decrease （82%-69%） in COD removal with decreasing HRT was apparent in UASF reactor. In case of UASB reactor, this decrease was marginal because addition of GLSS device significantly improved （14%-20%） the overall efficiency of the UASB reactor. GLSS enhanced the efficiency of the UASB reactor by increasing the settleability of suspended particles and accelerating the coagulation of colloidal particles due to the velocity gradient.展开更多
Heat transfer characteristics are studied for gas carrying evaporation with fluidized solid particles in a vertical rectangular conduit. Experimental results show that heat transfer of gas carrying evaporation is enha...Heat transfer characteristics are studied for gas carrying evaporation with fluidized solid particles in a vertical rectangular conduit. Experimental results show that heat transfer of gas carrying evaporation is enhanced and the superheat of liquid in contact with heating surface lowers remarkably by introducing solid particles. Nucleate boiling on the heating surface is suppressed to a considerable degree. The mechanism of heat transfer enhancement by fluidized solid particles is analyzed with the consideration of collisions of solid particles with the boiling vapor bubbles.展开更多
The hydrodynamics is still not fully understood in the three-phase stirred tank equipped with multi-impeller due to the intensive interaction between phases.In this work,the solid critical suspension speed(NJSG),relat...The hydrodynamics is still not fully understood in the three-phase stirred tank equipped with multi-impeller due to the intensive interaction between phases.In this work,the solid critical suspension speed(NJSG),relative power demand(RPD)and overall gas holdup(ε_G)were measured in an air–water–glass beads stirred tank equipped with multi-impeller,which consists of a parabolic blade disk turbine below two down-pumping hydrofoils.Results show that either the NJSGor the specific power consumption increases when increasing the volumetric solid concentration or superficial gas velocity.RPD changes less than 10%when solid volumetric concentration ranges from 0 to 15%.ε_G decreases with the increase of solid concentration,and increases with the increase of both superficial gas velocity and the total specific power consumption.The quantitative correlations of NJSG,RPD andεGwere regressed as the function of superficial gas velocity,specific power consumption,Froude number and gas flow number,in order to provide the reference in the design of such three-phase stirred tank with similar multi-impellers.展开更多
A three-dimensional （3D） finite element model of air-cushion isolated arch dam is presented with the nonlinear gas-liquid-solid multi-field dynamic coupling effect taken into account.In this model,the displacement f...A three-dimensional （3D） finite element model of air-cushion isolated arch dam is presented with the nonlinear gas-liquid-solid multi-field dynamic coupling effect taken into account.In this model,the displacement formulation in Lagrange method,pressure formulation in Euler method,nonlinear contact model based on Coulomb friction law are applied to the air-cushion,reservoir and contraction joint domain,respectively.The dynamic response of Jinping I arch dam with a height of 305 m is analyzed using the seismic records of the Wenchuan Earthquake in 2008.Numerical results show that the air-cushion isolation reduces significantly the hydrodynamic pressure as well as the opening width for the contraction joints of high arch dam.展开更多
A coal slurry mixing tank is a key piece of equipment in the preparation of coal slurry for direct coal liquefaction.It is a gas-liquid-solid three-phase mixing device.Based on the performance of the existing coal slu...A coal slurry mixing tank is a key piece of equipment in the preparation of coal slurry for direct coal liquefaction.It is a gas-liquid-solid three-phase mixing device.Based on the performance of the existing coal slurry mixing equipment,a type of test equipment for horizontal continuous coal slurry preparation was developed,but to this point has limited research results.The test equipment consists of a mixing cylinder,mixer,stirring impeller and other components.Slurry mixing experiments were undertaken using the prototype,testing the performance of the device.A mathematical model was proposed specifically for the operation of a coal slurry mixing tank that is horizontally operated with high slurry concentration and rotary flow.The flow field in the horizontal coal mixing tank was simulated with the computational fluid dynamic (CFD) method.The experimental results match well with the CFD simulation results.Results show that the test device of a coal slurry mixing tank can be used to model the mixing of pulverized coal and the solvent oil.A strong correlation was obtained.展开更多
Hydrodynamics of conical fluidized bed differ from that of columnar beds by the fact that a velocity gradient exists along the axial direction of the bed.The gas–liquid–solid fluidized bed has emerged in recent year...Hydrodynamics of conical fluidized bed differ from that of columnar beds by the fact that a velocity gradient exists along the axial direction of the bed.The gas–liquid–solid fluidized bed has emerged in recent years as one of the most promising devices for three-phase operations.Such a device is of considerable industrial importance as evident from its wide applications in chemical,refining,petrochemical,biochemical processing,pharmaceutical and food industries.To explore this,a series of experiments have been carried out for homogeneous well-mixed ternary mixtures of dolomite of varying compositions in a three-phase conical fluidized bed.The hydrodynamic characteristics determined included the bed pressure drop,bed fluctuation and bed expansion ratios.The single and combined effects of operating parameters such as superficial gas velocity,superficial liquid velocity,initial static bed height,average particle size and cone angle on the responses have been analyzed using response surface methodology(RSM).A 25 full factorial central composite experimental design has been employed.Analysis of variance(ANOVA) showed a high coefficient of determination value and satisfactory prediction second-order regression models have been derived.Experimental values of bed pressure drop,bed fluctuation and bed expansion ratios have been found to agree well with the developed correlations.展开更多
基金supported by the Natural Science Foundation Project of CQ CSTC (No. 2010BB7421)
文摘The gas-liquid-solid three-phase mixed flow is the most general in multiphase mixed transportation. It is significant to exactly solve the coupling hydraulic transient problems of this type of multiphase mixed flow in pipelines. Presently, the method of characteristics is widely used to solve classical hydraulic transient problems. However, when it is used to solve coupling hydraulic transient problems, excessive interpolation errors may be introduced into the results due to unavoidable multiwave interpolated calculations. To deal with the problem, a finite difference scheme based on the Steger- Warming flux vector splitting is proposed. A flux vector splitting scheme is established for the coupling hydraulic transient model of gas-liquid-solid three-phase mixed flow in the pipelines. The flux subvectors are then discretized by the Lax-Wendroff central difference scheme and the Warming-Beam upwind difference scheme with second-order precision in both time and space. Under the Rankine-Hugoniot conditions and the corresponding boundary conditions, an effective solution to those points located at the boundaries is developed, which can avoid the problem beyond the calculation region directly induced by the second-order discrete technique. Numerical and experimental verifications indicate that the proposed scheme has several desirable advantages including high calculation precision, excellent shock wave capture capability without false numerical oscillation, low sensitivity to the Courant number, and good stability.
基金Financial support from the National Natural Science Foundation of China(51076043 and 51061130538)Program for New Century Excellent Talents in University(NCET-09-0342)+1 种基金Central Universities(12QN02)111 Project(B12034)
文摘The computational fluid dynamics （CFD）-population balance equations （PBE） coupled model is employed to investigate the hydrodynamics in a gas-slurry internal loop reactor with external slurry circulation. The predicted radial profiles of local gas holdup and bubble diameter are in good agreement with the corresponding experimental data. The spatio-temporal velocity profile of the gas phase reveals that the upward movement of gas is slowed down and the residence time of gas is prolonged by the downward momentum of the slurry, introduction of the external slurry can greatly improve the uniformity of gas holdup distribution in the reactor, especially in the downcomer-tube action region. Moreover, the interaction between the downward slurry and upward gas can lead to small bubble size and high interfacial area as well as good mass and heat transfer. The above results suggest the function of external slurry circulation for the internal loop reactor and would be helpful for optimizing the design and scale up of reactors.
基金Supported by the National Natural Science Foundation of China (No. 29706006) and the General Corporation of Petrochemical Engineering of China (No.X598021).
文摘The local gas-phase flow characteristics such as local gas holdup(εg), local bubble velocity (V_b) and local bubble mean diameter(d_b) at a specified point in a gas-liquid-solid three-phase reversedflow jet loop reactor was experimentally investigated by a five-pointconductivity probe. The effects of gas jet flow rate, liquid jet flowrate, solid loading, nozzle diameter and axial position on the localεg, V_b and d_b profiles were discussed. The presence of solids atlow solid concentrations not only increased the local εg and V_b,but also decreased the local d_b. The optimum solid loading for themaximum local εg and V_b together with the minimum local d_b was0.16×10^-3 m^3, corresponding to a solid volume fraction ε_S＝2.5/100.
基金Supported by the National Natural Science Foundation of China(20990224,21121064,21206002)
文摘The parallel-competing iodide-iodate reaction scheme was used to study the micromixing performance in a multi-phase stirred tank of 0.3 m diameter.The impeller combination consisted of a half elliptical blade disk turbine below two down-pimping wide-blade hydrofoils,identified as HEDT + 2WH_D.Nitrogen and glass beads of100 μm diameter and density 2500 kg-m^(-3) were used as the dispersed phases.The micromixing could be improved by sparging gas because of its additional potential energy.Also,micromixing could be improved by the solid particles with high kinetic energy near the impeller tip.In a gas-solid-liquid system,the gas-liquid film vibration with damping,due to the frequent collisions between the bubbles and particles,led to the decrease of the turbulence level in the liquid and caused eventually the deterioration of the micromixing.A Damping Film Dissipation model is formulated to shed light on the above micromixing performances.At last,the micromixing time t_m according to the incorporation model varied from 1.9 ms to 6.7 ms in our experiments.
基金supported by the Youth Program of National Natural Science Foundation of China(Grant No.52104012)the Key Program of the National Natural Science Foundation of China(Grant No.51734010)the Key Natural Science Projects of Scientific Research Plan in Colleges and Universities of Xinjiang Uygur Autonomous Region(Grant No.XJEDU20211028).
文摘The multiphase flow characteristic is one of the most concerning problems during solid fluidization exploitation of marine natural gas hydrate reservoirs.In this research,a new transient gas-liquid-solid multiphase flow model with hydrate phase transition was developed.Meanwhile,this model considered the coupling relationship among convective heat transfer,hydrate dynamic decomposition,and multi-phase flow.The model can simulate the change of flow pattern from solid-liquid to gas-liquid-solid flow,and describe the distribution character of volume fraction of phase,wellbore temperature and pressure,and hydrate decomposition rate during transportation.The simulation results indicate that the hydrate decomposition region in the wellbore gradually expands,but the hydrate decomposition rate gradually decreases during the solid fluidization exploitation of hydrate.When mining time lasts for 4 h,and the bottom hole pressure decreases by about 0.4 MPa.Increasing NaCl concentration in seawater helps expand hydrate decomposition regions and improves the wellbore hydrate decomposition rate.When the Nacl mass fraction in seawater reaches 15%,it will raise the hydrate decomposition regions to the whole wellbore.In addition,the higher the wellhead backpressure,the lower the decomposition area and decomposition rate of hydrate in the wellbore.When wellhead backpressure reaches 2 MPa,the volume fraction of gas near the wellhead will reduce to about 12%.This work is expected to provide a theoretical basis for the development of marine hydrate reservoirs.
文摘The effects of liquid viscosities, solid circulating rates, liquid and gas velocities and phase holdups on the axial dispersion coefficient, Dax, were investigated in a gas-liquid-solid circulating fluidized bed (GLSCFB).Liquid viscosity promotes the axial liquid backmixing when solid particles and gas bubbles are present. Increases in gas velocities and solid circulating rates lead to higher Dax. The effects of liquid velocity on Dax are associated with liquid viscosity. Compared with conventional expanded beds, the GLSCFBs hold less axial liquid dispersion,approaching ideal plug-flow reactors.
基金supported by the projects of National Natural Science Foundation of China(grant Nos.52479102 and 52079067).
文摘Gas-liquid-solid three-phase flow is common in various fields,making it crucial to accurately and efficiently describe its dynamic behaviors.To better perform the gas-liquid-solid three-phase simulations,a coupling code based on GPU named as CoSim-FVDEM is developed,which combines the finite volume method(FVM)and the discrete element method(DEM).This code encompasses unresolved,resolved and resolved-unresolved coupling methods,making it suitable for three-phase flow simulations involving solid particles of various sizes.A series of cases are conducted to validate the accuracy of the developed coupling algorithm,including complex dam breach flow,water entry test of a single sphere and multi-sphere within rotating roller.Finally,a gas-liquid-solid three-phase flow numerical experiment is performed,which involves the bi-disperse granular systems in a rotating roller.Base on the numerical results,the dynamic behaviors of the three-phase flow are analyzed and the computational efficiency is evaluated.The results indicate that the developed coupling code can better be used for the dynamic analysis of large-scale gas-liquid-solid three-phase flow.
基金The authors are grateful to the National Natural Science Foundation of China(contract No.22178256)National Key Research and Development Program of China(contract No.2022YFF0705101)for financial support.
文摘Gas-liquid-solid mini-fluidized beds known for high efficiency with controllable mass and heat transfer characteristics,have good application prospects in fields such as multiphase reaction process enhancement and intrinsic kinetic detection.For three-phase mini-flow systems,the bed wall has a significant impact on spatiotemporal distribution of multi-phase flow structure,which influence the motion state of dispersed phase,make predicted phase holdup and residence time deviate from experimental values.However,current research on the quantitative impact of bed walls on flow structures is still limited,which hinders the optimization design and industrial application of such reactors.In this work,a meso-scale flow model of gas-liquid-solid mini-fluidized beds considering macro-scale effects between bed wall and flow is developed based on the principle of meso-scale science and introducing semi-theoretical formulas that take the effects of bed walls on particles and bubbles into account.The calculated values of this model are in good agreement with experimental data,where prediction of phase holdup fits well with experimental results,the deviation of bubble size and terminal velocity are within 10%.Compared to existing models,this model demonstrates a higher level of accuracy in predicting the flow patterns of mini-fluidized beds,particularly those with pronounced wall effect.This research has laid a foundation for the design,scale-up and industrial application of mini-fluidized bed reactors.
基金This work was supported by the National Natural Science Foundation of China(grant No.22008169)the Open Research Fund of State Key Laboratory of Multiphase Complex Systems(grant No.MPCS-2021-D-06).
文摘Gas-liquid-solid circulating fluidized bed(GLSCFB)is an important type of chemical reactor.The complex mesoscale flow structure of GLSCFB was described through the mesoscale flow structure parameters based on the energy-minimization multi-scale(EMMS)model.The liquid-solid drag force model(Drag-ls model)was proposed and it was found that the drag coefficient between liquid and solid in three-phase systems increased compared to liquid-solid two-phase systems because of the influence of gas phase.The gas-solid drag force model(Drag-gs model)was proposed based on a modified unified wake model.Furthermore,the combination of EMMS model and computational fluid dynamics(CFD)in GLSCFB was implemented,and the dynamic evolution process of particle clusters and distributions of gas holdup and solid holdup in GLSCFB were simulated more accurately by the models.The simulation results indicate that the drag forces exerted on the solid phase by both the liquid and gas phases are coupled and mutually influence each other.The simulated values of solid holdup may deviate from the experimental values if the interactions between the gas-solid and liquid-solid phases are corrected independently.When the average solid holdup of the bed is low,the mesoscale phenomena such as particle aggregation are not obvious.As the solid holdup increases,there is a significant phenomenon of particle aggregation in the bed.The particles undergo a spatiotemporal evolution process of forming elongated clusters with high solid holdup,spherical clusters with high solid holdup,and clusters with low solid holdup which has large surface areas.
基金the National Natural Science Foundation of China(grant No.22178256).
文摘The gas-liquid-solid mini fluidized bed(GLSMFB)combines the advantages of fluidized bed and micro-reactor,and meets the requirements for safety and efficiency of green development of process industry.However,there are few studies on its flow performance and no studies on its mass and heat transfer performance.In this paper,the characteristics of gas-liquid mass transfer in a GLSMFB were studied in order to provide basic guidance for the study of GLSMFB reaction performance and application.Using CO_(2)absorption by NaOH as the model process,the gas-liquid mass transfer performance of GLSMFB was investigated.The results show that the liquid volumetric mass transfer coefficient and the gas-liquid interfacial area both increase with the increase of the superficial gas velocity within the experimental parameter range under the same given superficial liquid velocity.At the same ratio of superficial gas to liquid velocity,the liquid volumetric mass transfer coefficient increases with the increase of the super-ficial liquid velocity.Fluidized solid particles strengthen the liquid mass transfer process,and the liquid volumetric mass transfer coefficient is about 13%higher than that of gas-liquid mini bubble column.
基金supported by the National Natural Science Foundation of China(Nos.91834303,22008169)the Open Research Fund of State Key Laboratory of Multiphase Complex Systems(No.MPCS-2019-D-11).
文摘The solid holdup,in a 150 mm-ID×2460 mm-height gas-liquid-solid expanded bed with air,water and glass beads(the diameter of particles is 0.6-0.8 mm)was firstly investigated based on the immersion-type online multiphase measuring instrument,and bubble behavior was studied via the BVW-2 double electrical conductivity probe.The effect of the superficial gas velocity and liquid velocity on the expanded ratio,the transition ratio,the bubble rising velocity,the gas holdup and the solid holdup was studied.It is discovered that compared with the gas velocity,the liquid velocity has stronger impact on the expanded ratio,but it is opposite for the transition ratio.The average gas holdup and solid holdup increase linearly as the superficial gas velocity goes up.Among it,the gas holdup increases greater in the center,while the solid holdup increases greater near the wall.Compared with it,when the superficial liquid velocity rises,the average gas holdup hardly changes,but the average solid holdup keeps decreasing,especially the solid holdup distributes flatter with the increase of the superficial liquid velocity.
文摘The hydrodynamics of a gas-liquid-solid fluidized bed was investigated by applying the S statistics method to pressure fluctuations measured under various operating conditions in a laboratory-scale bed. S statistics tests reveal the existence of three transition velocities, especially at low gas velocities. Four distinct fluidization regimes, namely, the compacted bed, agitated bed and coalesced and discrete bubble regimes were detected. A comparison of reconstructed attractors of pressure fluctuations measured at different axial positions along the riser and with various solid loadings showed significant differences in the signals compared before fluidization, especially at minimum liquid agitation velocity. Close to the minimum liquid fluidization velocity and high liquid velocities, the variation in particle size has an insignificant effect on the bed hydrodynamics. Therefore, S statistics is a reliable method to demar- cate different fluidization regimes and to characterize the influence of various operating conditions on the hydrodynamics of gas-liquid-solid fluidized beds. The method is applicable in large-scale industrial installations to detect dynamic changes within a bed, such as regime transitions or agglomeration.
基金supported by the National Natural Science Foundation of China(52074341)。
文摘This study proposes a novel cyclone separator with a conical inner core to enhance particle classification efficiency in oil and gas wellhead-recovered liquids.Particle motion and force dynamics are analyzed to optimize key structural parameters,including inlet diameter(D_i),overflow pipe diameter(D_(e)),insertion depth(L_(e)),and bottom flow pipe diameter(D_(z)).Numerical simulations employ the Reynolds stress turbulence model,SIMPLEC algorithm,and discrete phase model to evaluate separation performance in a gas-liquid two-phase system.Results indicate that a smaller D_i improves fine particle separation but increases turbulence;an optimal range of D_i/D_(c)=0.35-0.4 is recommended.Larger D_(e) enhances the diversion ratio,aiding fine particle discharge(D_(e)/D_(c)=0.25-0.35).Increased Le facilitates fine particle overflow but induces vortices,whereas a smaller L_(e) stabilizes the bottom flow for larger particle separation(L_(e)/D_(c)=0.5-0.75).A reduced D_(z) enhances centrifugal force and separation efficiency but may cause turbulence;an optimal D_(z)/D_(c) of 0.6-0.65 is suggested for stability.These findings provide valuable design guidelines for improving cyclone separator performance in multiphase flow applications.
基金supported by the National Research Foundation of Korea(NRF)under the Grant Numbers NRF-2021R1A2C2092146 and RS-2023-00282764.
文摘A numerical method is presented to simulate bubble–particle interaction phenomena in particle-laden flows.The bubble surface is represented in an Eulerian framework by a volume-of-fluid(VOF)method,while particle motions are predicted in a Lagrangian framework.Different frameworks for describing bubble surfaces and particles make it difficult to predict the exact locations of collisions between bubbles and particles.An effective bubble,defined as having a larger diameter than the actual bubble represented by the VOFmethod,is introduced to predict the collision locations.Once the collision locations are determined,the attachment of particles to the bubble surface is determined using a novel numerical algorithm based on collision/induction times.The proposed numerical method is validated through simulations of a rising bubble moving through a layer of particles.The validity of the collision detection algorithm is examined by comparing the collision probability predicted by the present numerical method with that predicted from a theoretical relationship based on bubble/particle diameters.The attachment probability predicted by the present algorithm is found to agree well with that of an experiment.
文摘Sludge granulation and the effect of gas-liquid-solid separator （GLSS） design on the efficiency of upflow anaerobic sludge blanket （UASB） and upflow anaerobic sludge filter （UASF） reactors, operating at HRTs ranging from 3 to 12 h was investigated. VSS/TS ratio gradually increased in both the reactors with increasing sludge age （from 0.5 to more than 0.7 for UASB reactor and 0.012 to 0.043 for UASF reactor）. X-Ray diffraction analysis of the UASF sludge showed the presence of expanding clays revealing its additional absorption capability. Fuoraphyllite and albite precipitation related to excellular polymers of the microbial shell structure, showed the extended growth of microorganisms during sludge granulation. A gradual decrease （82%-69%） in COD removal with decreasing HRT was apparent in UASF reactor. In case of UASB reactor, this decrease was marginal because addition of GLSS device significantly improved （14%-20%） the overall efficiency of the UASB reactor. GLSS enhanced the efficiency of the UASB reactor by increasing the settleability of suspended particles and accelerating the coagulation of colloidal particles due to the velocity gradient.
基金the National Natural Science Foundation of China (No. 59576039).
文摘Heat transfer characteristics are studied for gas carrying evaporation with fluidized solid particles in a vertical rectangular conduit. Experimental results show that heat transfer of gas carrying evaporation is enhanced and the superheat of liquid in contact with heating surface lowers remarkably by introducing solid particles. Nucleate boiling on the heating surface is suppressed to a considerable degree. The mechanism of heat transfer enhancement by fluidized solid particles is analyzed with the consideration of collisions of solid particles with the boiling vapor bubbles.
基金the financial support from the National Key R&D Program of China(2017YFB0306703)the Fundamental Research Funds for the Central Universities(XK1802-1)the National Natural Science Foundation of China(No.21676007)。
文摘The hydrodynamics is still not fully understood in the three-phase stirred tank equipped with multi-impeller due to the intensive interaction between phases.In this work,the solid critical suspension speed(NJSG),relative power demand(RPD)and overall gas holdup(ε_G)were measured in an air–water–glass beads stirred tank equipped with multi-impeller,which consists of a parabolic blade disk turbine below two down-pumping hydrofoils.Results show that either the NJSGor the specific power consumption increases when increasing the volumetric solid concentration or superficial gas velocity.RPD changes less than 10%when solid volumetric concentration ranges from 0 to 15%.ε_G decreases with the increase of solid concentration,and increases with the increase of both superficial gas velocity and the total specific power consumption.The quantitative correlations of NJSG,RPD andεGwere regressed as the function of superficial gas velocity,specific power consumption,Froude number and gas flow number,in order to provide the reference in the design of such three-phase stirred tank with similar multi-impellers.
基金supported by the National Natural Science Foun-dation of China (90715026)
文摘A three-dimensional （3D） finite element model of air-cushion isolated arch dam is presented with the nonlinear gas-liquid-solid multi-field dynamic coupling effect taken into account.In this model,the displacement formulation in Lagrange method,pressure formulation in Euler method,nonlinear contact model based on Coulomb friction law are applied to the air-cushion,reservoir and contraction joint domain,respectively.The dynamic response of Jinping I arch dam with a height of 305 m is analyzed using the seismic records of the Wenchuan Earthquake in 2008.Numerical results show that the air-cushion isolation reduces significantly the hydrodynamic pressure as well as the opening width for the contraction joints of high arch dam.
基金Project (No. 2008C21021) supported by the Science and Technology Research Program of Zhejiang Province, China
文摘A coal slurry mixing tank is a key piece of equipment in the preparation of coal slurry for direct coal liquefaction.It is a gas-liquid-solid three-phase mixing device.Based on the performance of the existing coal slurry mixing equipment,a type of test equipment for horizontal continuous coal slurry preparation was developed,but to this point has limited research results.The test equipment consists of a mixing cylinder,mixer,stirring impeller and other components.Slurry mixing experiments were undertaken using the prototype,testing the performance of the device.A mathematical model was proposed specifically for the operation of a coal slurry mixing tank that is horizontally operated with high slurry concentration and rotary flow.The flow field in the horizontal coal mixing tank was simulated with the computational fluid dynamic (CFD) method.The experimental results match well with the CFD simulation results.Results show that the test device of a coal slurry mixing tank can be used to model the mixing of pulverized coal and the solvent oil.A strong correlation was obtained.
文摘Hydrodynamics of conical fluidized bed differ from that of columnar beds by the fact that a velocity gradient exists along the axial direction of the bed.The gas–liquid–solid fluidized bed has emerged in recent years as one of the most promising devices for three-phase operations.Such a device is of considerable industrial importance as evident from its wide applications in chemical,refining,petrochemical,biochemical processing,pharmaceutical and food industries.To explore this,a series of experiments have been carried out for homogeneous well-mixed ternary mixtures of dolomite of varying compositions in a three-phase conical fluidized bed.The hydrodynamic characteristics determined included the bed pressure drop,bed fluctuation and bed expansion ratios.The single and combined effects of operating parameters such as superficial gas velocity,superficial liquid velocity,initial static bed height,average particle size and cone angle on the responses have been analyzed using response surface methodology(RSM).A 25 full factorial central composite experimental design has been employed.Analysis of variance(ANOVA) showed a high coefficient of determination value and satisfactory prediction second-order regression models have been derived.Experimental values of bed pressure drop,bed fluctuation and bed expansion ratios have been found to agree well with the developed correlations.
