Fully resolved simulations of particulate and aggregative fluidization systems are performed suc-cessfully with the so-called combined lattice Boltzmann method and time-driven hard-sphere model (LBM-TDHS). In this m...Fully resolved simulations of particulate and aggregative fluidization systems are performed suc-cessfully with the so-called combined lattice Boltzmann method and time-driven hard-sphere model (LBM-TDHS). In this method, the discrete particle phase is described by time-driven hard-sphere model, and the governing equations of the continuous fluid phase are solved with lattice Boltz-mann method. Particle-fluid coupling is implemented by immersed moving boundary method. Time averaged flow structure of the simulated results show the formation of core-annulus structure and sigmoid distribution of voidage in the axial direction, which are typical phenomena in fluidization systems. Combining the results of the simulation, the energy consumption Nst for suspending and transporting solids is calculated from the direct numerical simulation (DNS) of fluidization, and the stability criterion Nst/NT = rain proposed in EMMS/bubbling model is verified numerically. Further-more the numerical results show that the value of Nst/NT in particulate fiuidization is much higher than that in aggregative fluidization, but Nst/NT = rain is effective for both particulate and aggregative fluidization.展开更多
Melt flow can significantly change the transport of heat and solute,dendrite growth.In this work,a phase-field lattice-Boltzmann model was developed to studyα-Mg dendrite growth of Mg-5wt%Zn alloy with forced convect...Melt flow can significantly change the transport of heat and solute,dendrite growth.In this work,a phase-field lattice-Boltzmann model was developed to studyα-Mg dendrite growth of Mg-5wt%Zn alloy with forced convection.Results show that the existence of forced convection and overlap of thermal and solute fields makes thermal and solute fields distribution nonuniform.Thus,the symmetry of dendrite morphology is destroyed.The solid temperature and concentration of the downstream dendrite tip front with forced convection are higher than that without forced convection,while the concentration of the upstream dendrite tip front is lower.The solute transport through melt flow will be hindered by developed sidebranching.With flow velocity increase,the upstream temperature gradient and thickness of the downstream solute enrichment layer increase gradually,while the downstream temperature gradient and thickness of the upstream solute enrichment layer decrease gradually.Meanwhile,the upstream dendrite tip velocity will increase gradually,while the downstream dendrite tip velocity will decrease at first and then unchanged.This study is helpful to establish the relationship betweenα-Mg dendrite growth and melt flow,which is beneficial to understand the role of melt flow on dendrite morphologies.展开更多
Nano-porous materials have excellent thermal insulation performance,whose microstructure and physical properties,however,have great influence on the thermal conductivity.To accurately describe the stochastic phase dis...Nano-porous materials have excellent thermal insulation performance,whose microstructure and physical properties,however,have great influence on the thermal conductivity.To accurately describe the stochastic phase distribution,a random internal morphology and structure generation-growth method,called the quartet structure generation set(QSGS),has been proposed in the present paper.The model was then imported into lattice Boltzmann algorithm as a fully resolved geometry and used to investigate the effects on heat transfer at the nanoscale.Furthermore,a three-dimensional Lattice Boltzmann method(LBM)D3Q15 was adopted to predict the nano-granule porous material effective thermal conductivity.This ideal method provided a significant advantage over similar porous media methods by directly controlling and adjusting of granule characteristics such as granule size,porosity and pore size distributions and studying their influence directly on thermal conductivity.To verify the accuracy of the proposed model,some experiments based on guarded hot plate meter(GHPM)were conducted.The results indicated that the simulation results agreed well with the experimental data and references values,which illustrated that this method was reliable to generate the microstructure of nano-granule.What’s more,the effects of pressure,core distribution probability,cd and density were investigated.There existed an optimal density(about 120 kg·m^(-3))making the effective thermal conductivity being minimum and an optimal core distribution probability about cd=0.1 making the uniformity being the best.In addition,the present approach is applicable in dealing with other porous materials as well.展开更多
基金supported by the National Natural Science Foundation of China under Grant No.21106155the Chinese Academy of Sciences under Grant No.XDA07080303
文摘Fully resolved simulations of particulate and aggregative fluidization systems are performed suc-cessfully with the so-called combined lattice Boltzmann method and time-driven hard-sphere model (LBM-TDHS). In this method, the discrete particle phase is described by time-driven hard-sphere model, and the governing equations of the continuous fluid phase are solved with lattice Boltz-mann method. Particle-fluid coupling is implemented by immersed moving boundary method. Time averaged flow structure of the simulated results show the formation of core-annulus structure and sigmoid distribution of voidage in the axial direction, which are typical phenomena in fluidization systems. Combining the results of the simulation, the energy consumption Nst for suspending and transporting solids is calculated from the direct numerical simulation (DNS) of fluidization, and the stability criterion Nst/NT = rain proposed in EMMS/bubbling model is verified numerically. Further-more the numerical results show that the value of Nst/NT in particulate fiuidization is much higher than that in aggregative fluidization, but Nst/NT = rain is effective for both particulate and aggregative fluidization.
基金the National Natural Science Foundation of China(Nos.52074246,52275390,52205429,52201146)the National Defense Basic Scientific Research Program of China(Nos.JCKY2020408B002,WDZC2022-12)+2 种基金the Key Research and Development Program of Shanxi Province(Nos.202102050201011,202202050201014)the Science and Technology Major Project of Shanxi Province(Nos.20191102008,20191102007)the Guiding Local Science and Technology Development Projects by the Central Government(Nos.YDZJSX2022A025,YDZJSX2021A027).
文摘Melt flow can significantly change the transport of heat and solute,dendrite growth.In this work,a phase-field lattice-Boltzmann model was developed to studyα-Mg dendrite growth of Mg-5wt%Zn alloy with forced convection.Results show that the existence of forced convection and overlap of thermal and solute fields makes thermal and solute fields distribution nonuniform.Thus,the symmetry of dendrite morphology is destroyed.The solid temperature and concentration of the downstream dendrite tip front with forced convection are higher than that without forced convection,while the concentration of the upstream dendrite tip front is lower.The solute transport through melt flow will be hindered by developed sidebranching.With flow velocity increase,the upstream temperature gradient and thickness of the downstream solute enrichment layer increase gradually,while the downstream temperature gradient and thickness of the upstream solute enrichment layer decrease gradually.Meanwhile,the upstream dendrite tip velocity will increase gradually,while the downstream dendrite tip velocity will decrease at first and then unchanged.This study is helpful to establish the relationship betweenα-Mg dendrite growth and melt flow,which is beneficial to understand the role of melt flow on dendrite morphologies.
基金financially supported by the Natural Sciences Foundation of Shanghai,China(Grant No.15ZR1419900)。
文摘Nano-porous materials have excellent thermal insulation performance,whose microstructure and physical properties,however,have great influence on the thermal conductivity.To accurately describe the stochastic phase distribution,a random internal morphology and structure generation-growth method,called the quartet structure generation set(QSGS),has been proposed in the present paper.The model was then imported into lattice Boltzmann algorithm as a fully resolved geometry and used to investigate the effects on heat transfer at the nanoscale.Furthermore,a three-dimensional Lattice Boltzmann method(LBM)D3Q15 was adopted to predict the nano-granule porous material effective thermal conductivity.This ideal method provided a significant advantage over similar porous media methods by directly controlling and adjusting of granule characteristics such as granule size,porosity and pore size distributions and studying their influence directly on thermal conductivity.To verify the accuracy of the proposed model,some experiments based on guarded hot plate meter(GHPM)were conducted.The results indicated that the simulation results agreed well with the experimental data and references values,which illustrated that this method was reliable to generate the microstructure of nano-granule.What’s more,the effects of pressure,core distribution probability,cd and density were investigated.There existed an optimal density(about 120 kg·m^(-3))making the effective thermal conductivity being minimum and an optimal core distribution probability about cd=0.1 making the uniformity being the best.In addition,the present approach is applicable in dealing with other porous materials as well.