The multi-scale structures of complex flows have been great challenges to both theoretical and engineer-ing researches, and multi-scale modeling is the natural way in response. Particle methods (PMs) are ideal constit...The multi-scale structures of complex flows have been great challenges to both theoretical and engineer-ing researches, and multi-scale modeling is the natural way in response. Particle methods (PMs) are ideal constitutors and powerful probes of multi-scale models, owing to their physical insight and computational simplicity. In this paper, the role of different PMs for multi-scale modeling of complex flows is critically reviewed and possible development of PMs in this background is prospected, with the emphasis on pseudo-particle modeling (PPM). The performances of some different PMs are compared in simulations and new devel-opment in the fundamentals and applications of PPM is also reported, demonstrating PPM as a unique PM for multi-scale modeling.展开更多
Restitution is an important physical and mechanical property of granular materials. However, measuring its values in instantaneous collisions between particles is very difficult, especially for ore particles of irregu...Restitution is an important physical and mechanical property of granular materials. However, measuring its values in instantaneous collisions between particles is very difficult, especially for ore particles of irregular shapes. In this paper, restitution is measured indirectly and statistically with two cameras recording from different angles the trajectories of the ore particles rebounding from a steel plate. The momenta of the particles prior to and after the collision are calculated from the trajectories to give the restitutions of these collisions. The restitution between ore particles is then derived from the restitution of a steel ball with the steel plate measured in the same way. The approach has been proved to be practical and reliable for a variety of ore particles with moderate restitutions.展开更多
The hydrodynamic behavior of fine powders in jet-fluidized beds was studiednumerically and experimentally. The starting point of numerical simulation was the generalizedNavier-Stokes (N-S) equations for the gas and so...The hydrodynamic behavior of fine powders in jet-fluidized beds was studiednumerically and experimentally. The starting point of numerical simulation was the generalizedNavier-Stokes (N-S) equations for the gas and solids phases. The κ-ε turbulence model was used forhigh-speed gas jets in fluidized beds. Computation shows that a suitable turbulence model isnecessary to obtain agreement between the simulation and literature experimental data for ahigh-speed gas jet. The model was applied to simulating the fluidization of fine powders influidized beds with an upward or a downward air jet. An empirical cohesion model was obtained bycorrelating the cohesive force between fine particles using a cohetester. The cohesion model wasembedded into the two-fluid model to simulate the fluidization of fine powders in two-dimensional(2-D) beds. To study the fluidization behavior of fine and cohesive powders with a downward jet,experiments were performed in a 2-D bed. Agreement between the computed time-averaged porosity andmeasured data was obtained. With an upward jet in the bed center, the measured and computedporosities show a dilute central core, especially at very high jet velocities. Based on ourexperiments and computations, a downward jet located inside the bed is recommended to achieve bettermixing and contacting of gas and solids.展开更多
Recent referential studies on combustion synthesis of titania nanoparticles were briefly reviewed. Com-putations based on the minimization of Gibbs free energy were conducted to find the equilibrium compositions, the ...Recent referential studies on combustion synthesis of titania nanoparticles were briefly reviewed. Com-putations based on the minimization of Gibbs free energy were conducted to find the equilibrium compositions, the op-timal reaction temperature, the suitable mole ratio of oxygen to titanium tetrachloride, and the best inlet positions of tita-nium tetrachloride. The mean particle diameter was obtained from particle-dynamic simulation. A combustion apparatus was setup to synthesize titania nanoparticles by the oxidation and hydrolysis of titanium tetrachloride at high tempera-tures. Experimental investigation verified some results obtained from thermodynamic and particle-dynamic computations.展开更多
A new process is proposed to utilize refined ilmenite with high magnesia and calcia contents, which is the main secondary resource from vanadium-bearing titaniferous magnetite in Panzhihua, covering about 40% of the w...A new process is proposed to utilize refined ilmenite with high magnesia and calcia contents, which is the main secondary resource from vanadium-bearing titaniferous magnetite in Panzhihua, covering about 40% of the worlds titanium. The refined ilmenite was first deoxidized to separate the iron in the ore in order to enrich the titanium. The mechanism of chlorination of the titanium-rich slag was analyzed using the HSC chemistry software. Following deoxida-tion, a tandem fluidized bed was applied to chlorinating the titanium-rich slag. Modeling of the tandem fluidized bed ex-plains how this serial operation can effectively improve the convention ratio of TiO2 to TiCl4.展开更多
A theory of nonfluidized gas-solids flow, which combines the theory of multiphase flow with the mechanics of particulate media, was proposed on the basis of understanding that the particles contact each other, solids ...A theory of nonfluidized gas-solids flow, which combines the theory of multiphase flow with the mechanics of particulate media, was proposed on the basis of understanding that the particles contact each other, solids and gas are in movement, and the drag force on the particles caused by interstitial gas flow is similar to gravity force having the property of mass force. Then this theory was verified by experiments on vertical and inclined moving beds, and was applied to calculation and design of equipment and devices with moving beds, such as pneumatic moving bed transport, dipleg, V-value, L-valve, orifice flow, and arching prevention. It can be used to guide the design and operation of moving beds and fixed beds.展开更多
The multi-scale characteristics of clusters in a fast fluidized bed and of agglomerates in a fluidized bed of cohesive particles are discussed on the basis of large amounts of experiments. The cluster size and concent...The multi-scale characteristics of clusters in a fast fluidized bed and of agglomerates in a fluidized bed of cohesive particles are discussed on the basis of large amounts of experiments. The cluster size and concentration are dominated by the local voidage of the bed. A cluster consists of many sub-clusters with different sizes and discrete par-ticles, and the sub-cluster size probability density distribution appears as a negative exponential function. The agglom-erates in a fluidized bed of cohesive particles also possess the multi-scale nature. The large agglomerates form a fixed bed at the bottom, the medium agglomerates are fluidized in the middle, and the small agglomerates and discrete parti-cles become the dilute-phase region in the upper part of the bed. The agglomerate size is mainly affected by cohesive forces and gas velocity. The present models for predicting the size of clusters and agglomerates can not tackle the in-trinsic mechanism of the multi-scale aggregation, and a challenging problem for establishing mechanistic model is put forward.展开更多
The multi-scale structures of complex flows in chemical engineering have been great challenges to the design and scaling of such systems, and multi-scale modeling is the natural way in response. Particle methods (PMs)...The multi-scale structures of complex flows in chemical engineering have been great challenges to the design and scaling of such systems, and multi-scale modeling is the natural way in response. Particle methods (PMs) are ideal constituents and powerful tools of multi-scale models, owing to their physical fidelity and computational simplicity. Especially, pseudo-particle modeling (PPM, Ge & Li, 1996; Ge & Li, 2003) is most suitable for molecular scale flow prediction and exploration of the origin of multi-scale structures; macro-scale PPM (MaPPM, Ge & Li, 2001) and similar models are advantageous for meso-scale simulations of flows with complex and dynamic discontinuity, while the lattice Boltzmann model is more competent for homogeneous media in complex geometries; and meso-scale methods such as dissipative particle dynamics are unique tools for complex fluids of uncertain properties or flows with strong thermal fluctuations. All these methods are favorable for seamless interconnection of models for different scales. However, as PMs are not originally designed as either tools for complexity or constituents of multi-scale models, further improvements are expected. PPM is proposed for microscopic simulation of particle-fluid systems as a combination of molecular dynamics (MD) and direct simulation Monte-Carlo (DSMC). The collision dynamics in PPM is identical to that of hard-sphere MD, so that mass, momentum and energy are conserved to machine accuracy. However, the collision detection procedure, which is most time-consuming and difficult to be parallelized for hard-sphere MD, has been greatly simplified to a procedure identical to that of soft-sphere MD. Actually, the physical model behind such a treatment is essentially different from MD and is more similar to DSMC, but an intrinsic difference is that in DSMC the collisions follow designed statistical rules that are reflection of the real physical processes only in very limited cases such as dilute gas. PPM is ideal for exploring the mechanism of complex flows a展开更多
Meso-scale structures existing in the form of particle-rich clusters, streamers or strands in circulating fluidized beds, and of ascending bubble plumes and descending liquid-rich vortices in bubble columns and slurry...Meso-scale structures existing in the form of particle-rich clusters, streamers or strands in circulating fluidized beds, and of ascending bubble plumes and descending liquid-rich vortices in bubble columns and slurry-bed reactors, as commonly observed, have played an important role in the macro-scale behavior of particle-fluid systems. These meso-scale structures span a wide range of length and time scales, and their origin, evolution and influence are still far from being well understood.展开更多
Self-organization in thin micro-films has shown potential for the production of microelements with specific structures and functions; however, little is known about its mechanism of formation. A 2-D molecular dynamics...Self-organization in thin micro-films has shown potential for the production of microelements with specific structures and functions; however, little is known about its mechanism of formation. A 2-D molecular dynamics (MD) simulation on this process is carried out in this paper for films between two parallel walls (substrates) under different initial conditions. The films consist of two immiscible components (A and B). The simulation results in alternative columns perpendicular to the walls, which are rich either in A or in B molecules, respectively, apparently owing to their different interactions with the walls. The characteristic breadths of the columns depend on the distance between the two walls. By providing microscopic details of the self-organization processes and the resulted structures, MD simulation proves itself as a unique way for analyzing the dynamics of thin films.展开更多
This paper presents some remarks on the perspectives of process engineering in the 21st century extracted from the discussion at the workshop. It is considered that the field will be upgraded by introducing knowledge ...This paper presents some remarks on the perspectives of process engineering in the 21st century extracted from the discussion at the workshop. It is considered that the field will be upgraded by introducing knowledge in other fields, extended to even more applications by generalizing the relevant methods, and unified to, at least covered by, the complexity science. Transdisciplinarity is necessary to cope with this challenge.展开更多
While science continues to extend to two extremes - micro-scale towards dimensions even smaller than elemental particles and mega-scale even beyond the universe, one recognizes that reductionism is not sufficient to s...While science continues to extend to two extremes - micro-scale towards dimensions even smaller than elemental particles and mega-scale even beyond the universe, one recognizes that reductionism is not sufficient to solve many problems we encounter in engineering, which are likely characterized by nonlinearity, nonequilibrium and dissipative multi-scale structures. On the other hand, the common features of these nonlinear systems, such as bifurcation, state multiplicity and self-organization, have attracted much attention, leading to the approaches of the so-called complexity science which has become a focus not only in natural science and engineering science, but also in social science. However, no effective methodology has been established to understand these complex systems, though noticeable progress has been achieved in studying these systems, such as particle-fluid multi-phase systems. Multi-scale methodology has been considered as a promising methodology to tackle complex systems due to its capability in correlating phenomena at different scales. In this presentation, we shall review the development of the multi-scale methodology and its applications to particle-fluid systems, elucidating the essential relevance of complex systems and the challenging problems in chemical engineering. Multi-scale structure is considered to be the focus in studying complex systems, particularly, correlation between phenomena at different scales, compromise between different dominant mechanisms, coupling between spatial and temporal structural changes and critical phenomena occurring in these systems - these are the four critical issues in understanding complex systems. We first propose that by analyzing particle-fluid systems complex systems can be formulated as a multi-objective variational problem. Such an analytical multi-scale method will be reviewed in particular by analyzing the above four critical issues and by showing its 20-year development at IPE from a rough idea to modeling approaches, softwares and finally to in展开更多
基金the National Natural Science Foundation of China(Grant Nos.20336040 , 20490201)the Chinese Academy of Sciences(Grant No.INF105-SCE-2-07).
文摘The multi-scale structures of complex flows have been great challenges to both theoretical and engineer-ing researches, and multi-scale modeling is the natural way in response. Particle methods (PMs) are ideal constitutors and powerful probes of multi-scale models, owing to their physical insight and computational simplicity. In this paper, the role of different PMs for multi-scale modeling of complex flows is critically reviewed and possible development of PMs in this background is prospected, with the emphasis on pseudo-particle modeling (PPM). The performances of some different PMs are compared in simulations and new devel-opment in the fundamentals and applications of PPM is also reported, demonstrating PPM as a unique PM for multi-scale modeling.
文摘Restitution is an important physical and mechanical property of granular materials. However, measuring its values in instantaneous collisions between particles is very difficult, especially for ore particles of irregular shapes. In this paper, restitution is measured indirectly and statistically with two cameras recording from different angles the trajectories of the ore particles rebounding from a steel plate. The momenta of the particles prior to and after the collision are calculated from the trajectories to give the restitutions of these collisions. The restitution between ore particles is then derived from the restitution of a steel ball with the steel plate measured in the same way. The approach has been proved to be practical and reliable for a variety of ore particles with moderate restitutions.
基金supported by the National Natural Science Foundation of China(NNSFC,No.20476065)the Scientific Re-search Foundation for the Retumed Overseas Chinese Scholars of State Education Ministry(SRF for ROCS,SEM)Multi-Phase Reaction Laboratory(MPR)at the Institute of Process Engineering(IPE),Chinese Academy of Sciences(CAS).
文摘The hydrodynamic behavior of fine powders in jet-fluidized beds was studiednumerically and experimentally. The starting point of numerical simulation was the generalizedNavier-Stokes (N-S) equations for the gas and solids phases. The κ-ε turbulence model was used forhigh-speed gas jets in fluidized beds. Computation shows that a suitable turbulence model isnecessary to obtain agreement between the simulation and literature experimental data for ahigh-speed gas jet. The model was applied to simulating the fluidization of fine powders influidized beds with an upward or a downward air jet. An empirical cohesion model was obtained bycorrelating the cohesive force between fine particles using a cohetester. The cohesion model wasembedded into the two-fluid model to simulate the fluidization of fine powders in two-dimensional(2-D) beds. To study the fluidization behavior of fine and cohesive powders with a downward jet,experiments were performed in a 2-D bed. Agreement between the computed time-averaged porosity andmeasured data was obtained. With an upward jet in the bed center, the measured and computedporosities show a dilute central core, especially at very high jet velocities. Based on ourexperiments and computations, a downward jet located inside the bed is recommended to achieve bettermixing and contacting of gas and solids.
文摘Recent referential studies on combustion synthesis of titania nanoparticles were briefly reviewed. Com-putations based on the minimization of Gibbs free energy were conducted to find the equilibrium compositions, the op-timal reaction temperature, the suitable mole ratio of oxygen to titanium tetrachloride, and the best inlet positions of tita-nium tetrachloride. The mean particle diameter was obtained from particle-dynamic simulation. A combustion apparatus was setup to synthesize titania nanoparticles by the oxidation and hydrolysis of titanium tetrachloride at high tempera-tures. Experimental investigation verified some results obtained from thermodynamic and particle-dynamic computations.
文摘A new process is proposed to utilize refined ilmenite with high magnesia and calcia contents, which is the main secondary resource from vanadium-bearing titaniferous magnetite in Panzhihua, covering about 40% of the worlds titanium. The refined ilmenite was first deoxidized to separate the iron in the ore in order to enrich the titanium. The mechanism of chlorination of the titanium-rich slag was analyzed using the HSC chemistry software. Following deoxida-tion, a tandem fluidized bed was applied to chlorinating the titanium-rich slag. Modeling of the tandem fluidized bed ex-plains how this serial operation can effectively improve the convention ratio of TiO2 to TiCl4.
文摘A theory of nonfluidized gas-solids flow, which combines the theory of multiphase flow with the mechanics of particulate media, was proposed on the basis of understanding that the particles contact each other, solids and gas are in movement, and the drag force on the particles caused by interstitial gas flow is similar to gravity force having the property of mass force. Then this theory was verified by experiments on vertical and inclined moving beds, and was applied to calculation and design of equipment and devices with moving beds, such as pneumatic moving bed transport, dipleg, V-value, L-valve, orifice flow, and arching prevention. It can be used to guide the design and operation of moving beds and fixed beds.
文摘The multi-scale characteristics of clusters in a fast fluidized bed and of agglomerates in a fluidized bed of cohesive particles are discussed on the basis of large amounts of experiments. The cluster size and concentration are dominated by the local voidage of the bed. A cluster consists of many sub-clusters with different sizes and discrete par-ticles, and the sub-cluster size probability density distribution appears as a negative exponential function. The agglom-erates in a fluidized bed of cohesive particles also possess the multi-scale nature. The large agglomerates form a fixed bed at the bottom, the medium agglomerates are fluidized in the middle, and the small agglomerates and discrete parti-cles become the dilute-phase region in the upper part of the bed. The agglomerate size is mainly affected by cohesive forces and gas velocity. The present models for predicting the size of clusters and agglomerates can not tackle the in-trinsic mechanism of the multi-scale aggregation, and a challenging problem for establishing mechanistic model is put forward.
文摘The multi-scale structures of complex flows in chemical engineering have been great challenges to the design and scaling of such systems, and multi-scale modeling is the natural way in response. Particle methods (PMs) are ideal constituents and powerful tools of multi-scale models, owing to their physical fidelity and computational simplicity. Especially, pseudo-particle modeling (PPM, Ge & Li, 1996; Ge & Li, 2003) is most suitable for molecular scale flow prediction and exploration of the origin of multi-scale structures; macro-scale PPM (MaPPM, Ge & Li, 2001) and similar models are advantageous for meso-scale simulations of flows with complex and dynamic discontinuity, while the lattice Boltzmann model is more competent for homogeneous media in complex geometries; and meso-scale methods such as dissipative particle dynamics are unique tools for complex fluids of uncertain properties or flows with strong thermal fluctuations. All these methods are favorable for seamless interconnection of models for different scales. However, as PMs are not originally designed as either tools for complexity or constituents of multi-scale models, further improvements are expected. PPM is proposed for microscopic simulation of particle-fluid systems as a combination of molecular dynamics (MD) and direct simulation Monte-Carlo (DSMC). The collision dynamics in PPM is identical to that of hard-sphere MD, so that mass, momentum and energy are conserved to machine accuracy. However, the collision detection procedure, which is most time-consuming and difficult to be parallelized for hard-sphere MD, has been greatly simplified to a procedure identical to that of soft-sphere MD. Actually, the physical model behind such a treatment is essentially different from MD and is more similar to DSMC, but an intrinsic difference is that in DSMC the collisions follow designed statistical rules that are reflection of the real physical processes only in very limited cases such as dilute gas. PPM is ideal for exploring the mechanism of complex flows a
文摘Meso-scale structures existing in the form of particle-rich clusters, streamers or strands in circulating fluidized beds, and of ascending bubble plumes and descending liquid-rich vortices in bubble columns and slurry-bed reactors, as commonly observed, have played an important role in the macro-scale behavior of particle-fluid systems. These meso-scale structures span a wide range of length and time scales, and their origin, evolution and influence are still far from being well understood.
文摘Self-organization in thin micro-films has shown potential for the production of microelements with specific structures and functions; however, little is known about its mechanism of formation. A 2-D molecular dynamics (MD) simulation on this process is carried out in this paper for films between two parallel walls (substrates) under different initial conditions. The films consist of two immiscible components (A and B). The simulation results in alternative columns perpendicular to the walls, which are rich either in A or in B molecules, respectively, apparently owing to their different interactions with the walls. The characteristic breadths of the columns depend on the distance between the two walls. By providing microscopic details of the self-organization processes and the resulted structures, MD simulation proves itself as a unique way for analyzing the dynamics of thin films.
文摘This paper presents some remarks on the perspectives of process engineering in the 21st century extracted from the discussion at the workshop. It is considered that the field will be upgraded by introducing knowledge in other fields, extended to even more applications by generalizing the relevant methods, and unified to, at least covered by, the complexity science. Transdisciplinarity is necessary to cope with this challenge.
文摘While science continues to extend to two extremes - micro-scale towards dimensions even smaller than elemental particles and mega-scale even beyond the universe, one recognizes that reductionism is not sufficient to solve many problems we encounter in engineering, which are likely characterized by nonlinearity, nonequilibrium and dissipative multi-scale structures. On the other hand, the common features of these nonlinear systems, such as bifurcation, state multiplicity and self-organization, have attracted much attention, leading to the approaches of the so-called complexity science which has become a focus not only in natural science and engineering science, but also in social science. However, no effective methodology has been established to understand these complex systems, though noticeable progress has been achieved in studying these systems, such as particle-fluid multi-phase systems. Multi-scale methodology has been considered as a promising methodology to tackle complex systems due to its capability in correlating phenomena at different scales. In this presentation, we shall review the development of the multi-scale methodology and its applications to particle-fluid systems, elucidating the essential relevance of complex systems and the challenging problems in chemical engineering. Multi-scale structure is considered to be the focus in studying complex systems, particularly, correlation between phenomena at different scales, compromise between different dominant mechanisms, coupling between spatial and temporal structural changes and critical phenomena occurring in these systems - these are the four critical issues in understanding complex systems. We first propose that by analyzing particle-fluid systems complex systems can be formulated as a multi-objective variational problem. Such an analytical multi-scale method will be reviewed in particular by analyzing the above four critical issues and by showing its 20-year development at IPE from a rough idea to modeling approaches, softwares and finally to in
