The electrocatalytic process is a complex system engineering involving multiscale scientific problems. It is of great significance to explore and understand the mesoscale behavior of porous electrode electrocatalytic systems at different levels and scales, which is of great significance to further strengthen the electrocatalytic reaction and material diffusion and transfer, improve efficiency and reduce energy consumption. This paper gives a detailed review to the construction of hierarchically porous electrodes, tuning of the active sites located at the surfaces and interfaces, design and controlled preparation of mesoscale structures, the mesoscale characteristics and effects of the membrane materials. It is interesting to find that a deep understanding of the varied-level mesoscale mechanisms may lead to optimal and tunable design and preparation of porous electrodes, electrocatalysts, and membranes, and thus supply copious novel ideas and perspectives for forming a perfect and complete theory system for electrochemical catalysis.

Functional microparticle materials are widely used in many fields due to their unique characteristics of miniaturization and diverse functions. The versatile emulsion droplets from microfluidics provide excellent and unique templates for innovative design and controllable fabrication of functional microparticles. For microfluidic emulsion-template synthesis of functional microparticles, investigation on the formation and evolution of their meso-scale structures, the relationship between the interficial meso-scale structures of droplets and the dynamic behaviors of droplets, and the relationship between the coupled mass transfer-reaction and the meso-scale structures of microparticles, are of significant importance for rational control of the structures of emulsion templates and innovative fabrication of functional microparticlers. This review summarizes the recent progress on regulation of meso-scale structures for microfluidic emulsion-template synthesis of functional microparticles. Two aspects are mainly involved, including: (1) In the process for controllable microfluidic generation of emulsion templates, the relationship between the aggregation meso-scale structures of amphiphilic molecules at droplet interface and the droplet dynamics regarding motion, engulfment, coalescence, and interface evolution, and their influence on control of the morphology, structure and composition of the emulsion droplets; (2) In the process for emulsion template synthesis of functional microparticles, the rational control of trans-interfacial mass transfer, reaction and their coupling on the meso-scale structures of functional microparticles. This review could provide scientific guidance for the efficient fabrication and performance enhancement of novel functional microparticles.

Nucleation, as the first step in solution crystallization, is a key factor in determining the quality of crystalline products. Nucleation theory mainly includes classical nucleation theory and non-classical nucleation theory. Compared with the classical nucleation theory with uniform and stable structures such as atoms, ions, or molecules as units, non-classical nucleation theories often consider nanoscale precursors as units, such as ion-associated aggregates, nanoparticles and other non-uniform dynamic structures. As a result, the formation of non-classical nucleation processes is more complex. On the basis of traditional research methods of chemistry, chemical engineering and process systems engineering, it is necessary to make full use of mesoscale scientific research methods to complete the exploration of its core laws. This review summarizes the non-classical nucleation theories such as two-step nucleation theory, pre-nucleation cluster theory, and particle attachment crystallization theory, as well as other new theories proposed in recent years, and analyzes the mesoscale structure and its spatiotemporal dynamic behavior, the idea of revising and optimizing the existing nucleation mathematical model with mesoscale mathematical model is discussed, and the mesoscale research paradigm and theoretical development of crystal nucleation in solution crystallization are prospected.

The traditional hydrothermal synthesis of molecular sieve is not environmentally friendly in terms of the synthetic raw materials, because the silicon and aluminum reagents used in it are prepared from natural aluminosilicate minerals through a complex reaction and separation process. Using natural aluminosilicate minerals as silicon and aluminum sources to directly synthesize molecular sieve without chemical reagent intermediates is regarded as one of the promising research directions for green synthesis of molecular sieves. The key is the mesoscale activation of natural aluminosilicate minerals, which refers to the destruction of high-polymerization degree structure of natural aluminosilicate minerals and the depolymerization of them into molecular sieve synthetic raw materials with different mesoscale structures by means of physical, chemical or combination of physical and chemical action. From the perspective of energy consumption, activation mechanism and effect and the mesoscale structure of the activated products, the research advances of mesoscale activation methods for natural minerals are summarized and the widely used mesoscale activation method such as the mechanical activation, thermal activation, alkali fusion activation, sub-molten salt activation and quasi-solid-phase activation are introduced in detail. Based on the development process of mesoscale activation methods, the present situations of synthesizing high-performance molecular sieves from different mesoscale activation products are summarized, which provides important guiding strategy for the selection of mesoscale activation methods aimed to the synthesis of high-performance molecular sieve.

Based on the background of polyimide resin matrix composites for hypersonic aerospace, the key scientific problems and corresponding research ideas of mesoscale structure design and regulation are analyzed. This paper reviews the research progress in the relationship between structure and performance of thermoplastic polyimide, micro/nano interface intensification and dynamic monitoring of healthy structure based on composites at home and abroad, and the future development direction is proposed.

Water scarcity and pollution are one of most grand challenges facing humanity in the 21st century. Due to the low energy consumption and low cost, membrane technology is a green and efficient water treatment technology. Graphene oxide (GO) nanosheets with atomic thickness and excellent chemical stability have been recognized as an excellent two-dimensional (2D) membrane material, holding great promise in developing membranes for sustainable water treatment. In this paper, the development of GO membranes for water treatment is reviewed. Aiming to overcome two major challenges, low permeation flux and membrane fouling, of the membrane technology for water treatment, the mesoscale issues during the construction of nanochannels and surfaces of GO membranes are emphasized. In detail, the influence of the intercalator with different scales on the nanochannel structure and separation performance of the GO membranes is discussed. The antifouling strategies of GO membranes against foulants with different scales is analyzed. Finally, the brief summary and tentative perspectives of high permeation and antifouling graphene oxide membranes are presented.

The spontaneous aggregation of β-amyloid (amyloid β-protein, Aβ) forms a large number of toxic oligomers, which lead to the death of neurons in the brain, thereby causing cognitive impairment, namely Alzheimer's disease (AD). Serious threat to human health. At present, lack of the understanding of the multiscale Aβ oligomers has seriously restricted the design and development of Aβ modulators or inhibitors. This review is devoted to introduction of the fundamentals of the on-pathway Aβ aggregation and the relationship with mesoscience, classification of the various mesoscale Aβ oligomers generated during Aβ assembly, and the cytotoxicity mediated by the Aβ oligomers. Then, the design strategies, inhibitory mechanisms, and functions of different modulators or inhibitors developed to date are discussed. Finally, major challenges on the development of Aβ-associated AD drugs are addressed and the future research into this crucial field is proposed.

Ionic exchange membranes of three-phase structure including inert phase, ionic exchange group phase, and auxiliary functional group phase, are a kind of novel membrane materials. Traditional ionic membranes of two-phase structure are limited by the trade-off effect, and it is difficult to simultaneously improve the flux and selectivity. Therefore, researchers have been focused on the study of novel three-phase structure membranes to optimize ion transport pathway. In this paper, we summarize the development of ionic exchange membranes from two-phase to three-phase structure and describe three-phase structure membranes constructed from the micro-phase separation, polymers of intrinsic micropores, organic silane molecules, graphene oxide and metal organic frameworks. We highlight the mesoscale structure in ionic exchange membranes, including phase structure, pore structure and defects, as well as the application of these membranes in fuel cells, redox flow batteries, mono-/di-valent ion separation, and acid/alkali recovery. In order to provide strategies for improving the performance of ion exchange membranes by designing the three-phase structure.

Turbulence has always been viewed as a century lasting difficult problem in classic physics, and it was also viewed as a touchstone for verifying new theories and methods. The emerging mesoscience, developed from the energy-minimization multi-scale (EMMS) model in gas-solid fluidization, is devoted to the analysis of challenging mesoscale phenomena based on the view that the dominant factors are coordinated in competition. This article investigates the common principle for mesoscale behavior and recent viewpoints in turbulence through a mesoscience framework, including the compromise-in-competition between viscosity and inertia, as well as the turbulence stability condition. On this basis, EMMS-based turbulence model is developed and coupled with computational fluid dynamics (CFD), making a significant contribution to laminar-turbulent transition prediction and the improvement of global climate models. EMMS-based turbulence model successfully reproduces the compromise-in-competition between viscous and inertial dominant mechanisms in mesoregime, providing important proof that the mesoscience can be universal theory for complex system.

Mesoscale structures and mechanisms represent one of the critical scientific problems in process engineering such as chemical, metallurgy and energy industries. Although the mathematical model of multiphase flow has made great progress in the past few decades, there are several longstanding problems including the modeling accuracy dependent on adjustable parameters, the limited model applicability, and large computation cost, etc. It is difficult for the model development to adapt to the demand of current rapid development of new technology and new processes. In fact, the multi-fluid model based on the averaging method requires several sub-models to be closed, e.g., interphase forces, coalescence/breakup kernel functions, and turbulence models. These sub-models determine the simulation accuracy of the multi-fluid model. Developing mesoscale models from the perspective of mesoscience provides new avenue through analyzing the dominant mechanisms for the evolution of heterogeneous structures in multiphase flow to improve or reconstruct the closure model. In this paper, two types of mesoscale closed models based on mesoscale stability conditions are summarized: one is used for the momentum transfer between closed phases like mesoscale drag, the other is for the evolution of the characteristic parameters of discrete phases, e.g., the mesoscale population balance model, to calculate the bubble or droplet size distribution. Then, the application of these models in multiphase flow equipment such as fluidized bed, bubble column, airlift loop reactor, stirred tank, rotor-stator emulsification is reviewed, and the future study and key scientific issues are analyzed.

The gas-liquid-solid fluidized bed is an important multi-phase reactor and has a wide range of applications in the chemical and related process industries. However, due to the very limited quantitative description of the complex multiphase flow structure in this type of reactor, its design and scale-up still mainly rely on experience, resulting in a low scale-up success rate and unpredictable reaction results. Therefore, establishing and perfecting the three-phase flow mechanism model in the gas-liquid-solid fluidized bed is the key link to realize the scientific design and scale-up of this type of reactor. This paper analyzes the research progress on the flow mechanism models of gas-liquid-solid fluidized bed with liquid phase as the fluidization medium, especially summarizes the new progress of mesoscale model of gas-liquid-solid flow, and points out the existing problems and the direction of further research, hoping to be a reference for the basic researches and industrial applications.

Coal plays an important role in providing the basic energy security. Dry heavy-medium fluidized separation is an important part of coal separation and processing, which helps to promote the efficient and clean utilization of coal resources in China. Reliable separation is mainly based on the accurate density control in the separation process. And the core of density control is related to weakening the bubble evolution in the bed. It is comparably important to understand the tendency of bubble evolution and the principle of bubble dispersal. The research proposed the key scientific problems in dry fluidization separation process from mesoscale perspective. Furthermore, the research progress has been collected on the evolution of mesoscale structure on the view of lab system and scale-up of dry fluidization separation system. The mentioned research provided the detailed explanations on evolution of mesoscale structure. Meanwhile, the relevant methods have been put forward on the accurate regulation of mesoscale structure. It is also of great significance to the sorting and quality improvement of coal.

In gas-solid fluidized beds, spatiotemporal mutiscale structures caused by the intrinsic instability of gas-solid flows have a large impact on the interphase interaction. Predicting and controlling the hydrodynamic characteristics in fluidization remain a difficult task. To overcome this challenge, a constitution of the interphase interaction considering the effect of the inhomogeneous structures should be built. As a dominating factor in determining hydrodynamic characteristics of fluidization, the constitution of the mesoscale drag force attract increased attention in recent years. This paper briefly describes the effect of the inhomogeneous structures on the drag force, starting with the mechanisms of the generation and evolution of these structures. The filtered drag models are summarized from the perspective of modeling process. The developments of these models including improving the accuracy and effectivity, enhancing the generality for different material properties and flow regimes, and considering more physical mechanisms in actual systems have been reviewed. According to these studies, further work should be done to improve the generality and consider more physical mechanisms. Combining rational modeling of structural evolution mechanism and giving full play to the advantages of machine learning data analysis and processing is the key to the further development of drag modeling.

The mesoscale structure in the gas-solid fluidization bed seriously affects the macroscopic properties of fluidization, such as mass transfer, heat transfer, reaction efficiency, and so forth. Thus, the study of mesoscale structure is important. We briefly review the definition and classification of mesoscale structures in the fluidization system. Then, the causes of mesoscale structure formation are analyzed from the fluid-particle, particle-particle interactions (inelastic collision and forced perspective), based on summarizing the latest research progress. Primarily, we focus on the agglomerate, which system's relevant driving force or source of granular energy nanoparticles. The van der Waals force calculation is reviewed between fine particles and agglomerates' theoretical force balance model. It is very significant to study a dynamic of the mesoscale structure with inter-particle forces. It can provide precise control of the mesoscale structure technique and has broad application prospects in chemical engineering.

The jet flow induces an important mesoscale flow structure in the riser reactor, which has an important impact on the product yield, selectivity and coking on the inner wall of the riser. Research on gas jet hydrodynamics in a feedstock injection zone of a riser and the intensification strategy was reviewed in this paper. The secondary flow is the main reason for the unmatching concentration of feedstock and catalyst in a feedstock injection zone with traditional and upward jet injection scheme. Based on Kutta-Joukowski theorem, the formation mechanism of the secondary flow, the trajectories of the main flow and secondary flow, as well as the intensification strategy of feedstock-catalyst countercurrent contact were introduced and analyzed theoretically. Focusing on RFCC and pyridine synthesis processes, work associated with laboratory findings and commercialized units test were introduced in terms of intensification methods such as oil-catalyst countercurrent contact and dual layer nozzles. The results show that product yields increase and the coking inside the reactor is significantly relieved after the strategy was used.

Complex gas-solid fluidization systems with multiscale dynamic structures have been widely encountered in process industries. Understanding their hydrodynamic characteristics is essential for the proper design and scale-up of such reactors. The energy-minimization multi-scale (EMMS) method provides a general modeling idea for the quantitative characterization of gas-solid heterogeneous systems. In this paper, a concise introduction of the EMMS drag model for coarse-grid continuum simulation was first provided, with emphasis on our recent progress on the improvement and generalization of the drag model. The extension and application of the population balance model (PBM) in quantifying the dynamic evolution of bubbles or clusters in the fluidized beds were then discussed, followed by an overview of the integration of PBM and structure-dependent models. Finally, the application of EMMS theory in predicting the macroscopic steady-state dynamics of complex gas-solid reactors was also reviewed, together with the development of the steady-state EMMS models applicable for various regimes, the construction of generalized operating diagram and the realization of full-loop modeling of gas-solid circulating fluidized bed reactors.

The ion-electron transfer and heat transfer in the electrode significantly affect the electrochemical energy storage performance. The study of heat - mass transfer in porous electrodes, as a typical mesoscale problem, is of great significance to the design of high-performance electrochemical energy storage devices. At present, the simplified model of porous electrode can only approximate the real pore size distribution to a certain extent, and it is difficult to represent the diversified surface morphology and the complex distribution of catalytic active sites, which limits the in-depth study of heat-mass transfer in porous electrode. Therefore, a simulated annealing algorithm based on improved state updating random reconstruction method and dynamic annealing coefficient was used to reconstruct the two-dimensional SEM image after image segmentation into a real three-dimensional porous electrode. Then, the ion transport and electrode heat conduction models in real porous electrodes were established by reconstructing the PNP equation and Fourier law. The results show that when the charging time is 0.1 plate charging relaxation time, the ions mainly adsorb on the contact surface between the skeleton phase of the porous electrode and bulk phase, and the ions tend to migrate from the edge of the cross section to the center. In addition, since the actual thermal conduction distance is much smaller than the thickness of the porous electrode, the thermal relaxation time in the porous electrode is much smaller than that of the flat plate.

Porous materials play an important role in modern chemical industry, but the interfacial transfer phenomena caused by their nano-confinement pores cannot be ignored. For direct oxidation synthesizing hydrogen peroxide (H₂O₂), revealing the mesoscale relationship between mass transfer of desorbing H₂O₂ and reaction is the key to improving the yield. Linearized non-equilibrium thermodynamics has provided a unified framework for decoupling the interfacial diffusion and reaction, but in this case, a suitable method of measuring mass transfer flux was lacked. Therefore, the microcalorimetry experiments measuring the heat effect of interaction between porous carbons and H₂O₂ were designed in this paper. With the help of molecular simulation and pore characterization, the structures for interfacial transfer were revealed, and the quantitative mass transfer resistance analysis of non-equilibrium thermodynamics was realized, then the dynamic change of H₂O₂ concentration was obtained. The results showed that microcalorimetry is an effective linearized non-equilibrium thermodynamic resistance analysis method. Mesoporous structure, biological skeleton texture and supporting 1%(mass) palladium can enhance the mass transfer flux of H₂O₂ in porous carbon, but the realization of ultra-high flux requires the matching of diffusion and reaction resistance. The resistance decoupling of non-equilibrium thermodynamics is an important quantitative description method to reveal the mesoscale mechanism of heterogeneous reaction process, which is expected to provide a theoretical basis for the regulation and optimization of the process.

The mass transfer processes of the gas-liquid two-phase Taylor flow in the ultrasonic microreactor were simulated by CFD method. The spatial distribution and time evolution of the mesoscale structures including surface waves, acoustic streaming and local concentration were analyzed. The simulation results effectively captured the liquid film region and correlated the liquid film thickness with the surface wave vibration. The formation of acoustic streaming near the gas-liquid interface was also discussed. According to the mass transfer characteristics of ultrasonic Taylor flow, the effects of different flow and ultrasonic conditions on the mass transfer process at the liquid slug and film were investigated separately, and the contribution of each local part on the overall mass transfer efficiency was compared. The relationship between the overall and local Sh-Pe was analyzed to discuss the characterization method of the gas-liquid mass transfer rate under ultrasonic conditions. The analysis results verify the calculation of the mass transfer coefficient of the ultrasonic microreactor from the perspective of mesoscale, and improve the theory of strengthening the gas-liquid mass transfer process in the ultrasonic microreactor.

The flow patterns of liquid-liquid two-phase flow in T-shaped parallel microchannels are studied by using a high-speed camera system. The glycerol-water solution is used as the dispersed phase, and silicone oil with 5% Dowsil as the continuous phase. Four flow patterns of slug flow, droplet flow, annular flow and parallel flow are observed in parallel channels under different two-phase flow conditions. The diagram of flow patterns is constructed with the flow rates of the two-phase as the coordinate axes, and the transition lines of flow patterns are obtained. The influences of the viscosity of the continuous phase on the flow patterns and their transitions are investigated. As the viscosity of the continuous phase increases, the transition lines of flow patterns move downward, the region of the slug flow becomes smaller, and the region of the droplet flow becomes larger. The flow patterns of the droplet group in cavity are studied, and the mesoscale concept is used to analyze the effects of the behavior of the droplet group in cavity on the flow distribution. Four flow patterns in cavity are observed under different two-phase flow conditions, the flow patterns of the droplet group in cavity are mainly affected by the flow ratio of the two phases. The flow distribution is mainly controlled by the fluid resistance of the parallel channels and the mesoscale structure of the cavity. The influence of flow ratio of the two phases on flow distribution is studied and the dominant factor of flow distribution corresponding to different operating conditions is obtained. When the two-phase flow ratio is small, the flow distribution is dominated by the fluid resistance of the downstream channel, while when the two-phase flow ratio is large, it is dominated by the dynamics of the droplet population in the back cavity.

In the gas-liquid bubbling flow represented by the bubble column, there are two turbulence mechanisms, the bubble induced turbulence (BIT) and the shear turbulence, and they both compete and work together in different time and space ranges. There are uncertainties remain in how BIT affects the bubble breakage and coalescence, the interphase interaction forces and the mass transfer, due to the limited understanding of the BIT energy spectrum. Considering the joint effects of bubble-induced turbulence and shear turbulence, we proposed the bubble breakage model and the turbulence dispersion force model in dealing with the global or the local dominance of BIT. For different operating conditions, these models have performed well in capturing the dynamic behaviors of both the gas- and the liquid-phase, which offers fresh insights into understanding the mechanisms of the interphase mass transfer process in the gas-liquid bubbly flows.

In this paper, the influence of the concentration of acetic acid on the hydrodynamic parameters in the bubble column is investigated in the bubble column PX oxidation reactor using two-dimensional and three-dimensional CFD-PBM coupled model. The experimental data are obtained by differential pressure method, fiber optic probe and electrical resistance tomography (ERT) technique, and the simulation results are compared with the experimental values. The drag force model and the coalescence model are corrected by the surface tension term, and the modified model is used for numerical simulation in the acetic acid system with ambient temperature and ambient pressure. The simulation results of the hydrodynamic parameters are analyzed. The results show that when the concentration of acetic acid is in the range of 70%—80%(mass), the average gas holdup has a maximum value. The predicted value of the average gas holdup is within ±10% error, and the three-dimensional simulation results are in good agreement with the ERT experimental value. The modified model has better predictability in acetic acid systems with different concentrations.

Granular flow in silos is widely used in chemical reactions. Accurately grasping the dynamic law of granular flow is extremely important for regulating the mixing and transmission efficiency in chemical reaction process. Granular temperature is one of the important parameters affecting granular flow. In this paper, a speckle visibility spectroscopy measurement device based on linear CCD camera is built, and spherical particles with mean particle sizes of 0.94 and 1.55 mm were selected. By measuring the time-varying granular temperature during silo flow, it was found that the discrete particle motion is stable under mesoscale conditions. Further, comparing the granular temperature values of the two particle sizes, it is observed that the larger particle size has higher energy dissipation in the steady-state flow, so the relationship between the macro mass flow rate and the mesoscopic granular temperature is established. In addition, by analyzing the distribution characteristics of the particle temperature field in the silo, it is found that the discrete particles near the orifice have directional and orderly motion. Finally, according to the curve of granular temperature during the jamming in silos. the relaxation change law of clogging is revealed. The experimental results reveal the law of granular flow in the silo, which provides reference data for improving the storage and transportation of granular material in chemical production.

Mesoscale structures such as clusters are common in gas-solid two-phase flows. These mesoscale heterogeneous structures directly affect the gas-solid flow characteristics and gas-solid contact efficiency, and then affect the gas-solid interphase heat transfer, mass transfer and chemical reaction process. In the coarse grid method which is more suitable for industrial large-scale gas-solid heat transfer simulation, there is a lack of heterogeneous heat transfer model with high accuracy, simple and easy to use, and can consider the influence of mesoscale non-uniform structure. Computational fluid dynamics-discrete element method (CFD-DEM) is used to study the interphase heat transfer of gas-solid two-phase flow. In order to ensure the continuous heat transfer between gas and solid, two methods to maintain the temperature difference between gas and solid during the heat transfer procedure are adopted, and the advantages and disadvantages of the two methods are discussed. Method 1: add a heat source term to the gas phase energy equation; Method 2: reset the gas phase temperature at intervals and free heat transfer between the gas-solid two phases after resetting the temperature. The solid-phase temperature remains unchanged in both methods. The results show that the local gas-solid heat transfer per unit volume at the cluster interface is the largest. The ratio of local gas-solid heat transfer per unit volume to the total gas-solid heat transfer per unit volume at the dilute phase and the interface of the clusters in the testing temperature method is greater than that of the heat source term method, while the ratio of local gas-solid heat transfer per unit volume to the total gas-solid heat transfer per unit volume at the dense phase is less than that of the heat source term method. By filtering the CFD-DEM calculation data, a two parameter (filtered solid volume fraction and filter size) heat transfer coefficient correction factor model is constructed for the reset temperature method. The performance of the model is evaluated through a priori analysis. The results show that the proposed model is better than the existing two parameter model in the literature when the filter size in the range of 5 to 40 times the particle diameter.

Three kinds of particles, including sand, sand and fine silica powder mixed particles, are used in the experiment. Time series signals of solid holdup measured by optical fiber probe are statistically analyzed. A method of decoupling complex optical fiber signals was established. The threshold of bubble phase is determined by traversing method, and its accuracy is verified. Variation of the bubble threshold of different particles in radial direction is analyzed, and it is found that addition of fine particles helps to improve the fluidization quality. The threshold of bubble phase decrease with increasing superficial gas velocity. The criterion of particle agglomerate identification in the dense-phase bed is proposed. The characterization of mesoscale flow structure is realized, and a software for decoupling optical fiber signals is written. Mesoscale flow structures of sand and its mixed particles are analyzed. The fractions of bubble phase, emulsion phase and particle agglomerate are obtained. The result shows that addition of a small amount (5%,mass fraction) of fine particles can reduce the formation of agglomerate and significantly improve the fluidization quality. Addition of 10% fine particles will weaken the improvement of fluidization quality. An analysis of hydrodynamics of bubbles reveals that with addition of 10% fine particles, the chord length of bubbles increases and the frequency and rising velocity of bubbles decreases. An analysis of hydrodynamics of agglomerate reveals that the effect of superficial gas velocity on agglomerate velocity is weaken as the content of fine particles increases. With the increase of fine powder, the chord length of agglomerates decreases slightly. When the content of silica powder is 5%, the frequency of particle agglomeration is small and the radial distribution is uniform. When the content of silica powder is 10%, the frequency of agglomerates increases, indicating that adding too much fine powder will promote the formation of agglomerates.

Wet particle systems are very common in nature and industrial processes, such as spray granulation, mineral bonding in reactors, pharmaceutical and catalyst. Due to the presence of liquid, the flow, heat and mass transfer characteristics are significantly changed compared with dry particle systems. For example, a large number of typical mesoscale structures, including particle agglomeration, clusters and bubbles, form and lead to different flow regime. Thus, mesoscale structure flow and evolution behaviors have attracted more and more attention, which might affect the design and operation of industrial reactors. In this paper, typical mesoscale structures are investigated in a bubbling fluidized bed by discrete element method (DEM), and effect of external magnetic field on mesoscale structure evolution process is explored. First, the numerical model for describing dry and wet particle system flow behaviors were established with magnetic field introduced. The numerical model has been validated and shown in our previous published investigations. Then, mesoscale structure flow behaviors were analyzed in dry and wet particle system without magnetic flied. Bubble evolution process was found clearly in a dry particle system, and the trajectory of the bubble was almost along the midline of fluidized bed. With the cohesive liquid introduced, that of bubble center was offset from the midline. Next, an external magnetic field was introduced based on DEM to study the evolution mechanism of the mesoscale structure in the wet particle system under the action of the magnetic field. We compared the dominant role of liquid bridge force, contact force, magnetic force and drag force in fluidized beds, and tried to analyze and explore the relationship among different forces. The study found that without considering the magnetic field, particles are easy to form agglomeration and have irregular bubble boundaries. After the introduction of an external uniform magnetic field, the magnetic field force will destroy and inhibit the bubble structure in the bubbling fluidized bed.

In the start-up stage of a fluidized bed, the internal components will be impacted by a large destructive load. In order to ensure the long-term reliability of the internal components of the fluidized bed, it is necessary to master the force characteristics of the internal components in the fluidized bed at this stage. To this end, a method for statistically calculating the stress exerted on the internals from CFD-DEM simulation was proposed, and the simulation results were validated. It was found that the experimentally measured dynamic load impact can be reproduced semi-quantitatively, the effects of superficial gas velocity and particle properties on the load impact can also be predicted. Present study proved not only the correctness of the proposed statistical method, but also the feasibility of extracting the stress exerted on the internals using CFD-DEM method.

The multi-scale phenomenon in catalytic reaction process has been a hot research topic in the field of particle science in recent years, among which particle morphology and coke deposition are the key parameters that affect the catalyst flow and activity. In order to investigate coke influence on catalysts morphology,we have made five types of sample catalysts with different coke amount from the second generation zeolite SAPO-34 catalyst in DMTO process in our pilot fixed fluidized bed reactor under the condition of their residence in the reactor such as 0, 30, 60, 90 and 120 min separately. Particle size, sphericity, ellipse ratio, chroma and their distribution etc. were measured by image processing integrated with deep learning algorithm. The high-resolution images of the five samples were snapped by using an optical fiber endoscopic micro-scale imaging platform. The experimental results show that there exists the strong coke influence on catalysts size and its distribution. However, this effect on catalysts spherical or elliptical ratio is weak. Compared with the coke data measured by a thermogravimetric instrument, we have developed a coke-chromaticity method, which is a mathematical linear model between coke amount and the chromaticity of five catalysts samples. Two verification samples were chosen from the industrial catalysts used in a DMTO plant. The measurement relative error is less than 10% with a good consistency according to the coke data obtained by thermogravimetric device and that predicated by the coke-chromaticity method. This will provide a potential method for monitoring catalyst state in DMTO reactor and guiding its processing optimum operation.

Methanol to propylene (MTP) is the key technology in coal chemical industry. Coke is considered to be one of the important reasons for the inactivation of catalysts. In this study, the carbon-deposited zeolite was taken as the research object, and the structure-activity relationship among methanol adsorption behavior, surface acidity of molecular sieve, coke composition and methanol reactivity in MTP reaction was investigated by various characterization methods such as IGA, FTIR and TG. It was found that the adsorption capacity of methanol is decreased with the increase of carbon deposition, the decreasing rate is directly proportional to the methanol conversion. The main components of carbon species retained on the catalysts are light hydrocarbons, BTX aromatics, active coking and carbon deposition, and carbon deposition is the main reason for the deactivation of zeolites. Compared with the fresh catalyst, the completely inactivated catalyst still retains certain adsorption ability for methanol, and it is speculated that the carbon deposition mainly exists near the center of acid active site. The hydroxyl and bridge hydroxyl of B acid center are firstly occupied by carbon deposition, followed by extra-framework Al—OH; the methanol conversion was linearly correlated with B acid and L acid in zeolites. In addition, based on the proportional relationship between the deactivation rate of the catalyst and the conversion rate, combined with the reaction kinetics, the mathematical expression of the deactivation curve was deduced, which theoretically explained the mesoscale mechanism of carbon deposition deactivation during the MTP reaction.

Complex systems with multi-level and multi-scale structures are widely encountered in the structure optimization of catalysts and catalytic reaction process, from synthesis conditions to structure regulation of catalysts, from catalytic performance to the active sites regulation, it is important to understand mesoscale structure of catalytic system. In this paper, Fe-Mn catalyst precursors (Fe/Mn mole ratio 1/4) with different structures were prepared by four methods (low-temperature co-precipitation, deposition-precipitation, calcination of mixed precursors, and mechanical mixing). The relationship between their structure and activation process, distribution of iron carbides and the catalytic performance for preparation of olefins from syngas were investigated. The results showed that the synthesis method had a significant impact on the structure of the catalysts, which mainly reflected in three aspects: activation process, iron carbides size and catalytic performance. The Fe-Mn catalysts prepared by co-precipitation had shown a higher CO conversion rate (20.07%), olefin/paraffinratio (2.32), and iron space-time yield (4.37×10^-5 mol CO?(g Fe)^-1?s^-1), which were mainly due to the smaller particle size of iron-carbon compounds and more Fe₅C₂ active phases formed after the catalyst was activated.

As an important catalytic material, Beta zeolite is widely used in petrochemical, coal chemical and environmental protection fields, but its conventional hydrothermal synthesis process has problems such as high cost, low yield per kettle and large waste water discharge. This article presents a green and economic strategy to synthesize Beta zeolite from natural mineral via a mesoscale depolymerization-reorganization approach. The proposed methodology results in a Beta zeolite (denoted as Beta-Anhyd) owning abundant meso- and macro-pores, larger specific surface area and lower acid amount than a commercial sample (Beta-Ref). The Beta-Anhyd derived catalyst (Beta-Anhyd-Deal) that was prepared by a two-step post-synthesis method consisting of the dealumination of Beta-Anhyd and the incorporation of tin shows much better catalytic performance in the propane dehydrogenation reaction than the reference one (Beta-Ref-Deal).

Accurate prediction of bubble size and volumetric mass transfer coefficient is very important for the scale-up design of aerated-stirred industrial bioreactors, and thus it is necessary to establish a suitable bubble coalescence and breakup model to ensure the efficient operation of the reactor. In this work, taking a 5 L aerated agitated bioreactor as a sample, and based on experimental data of bubble size and volumetric mass transfer coefficient, the effects of two coalescence models and five breakup models on the simulated flow behavior and mass transfer capacity were investigated. The results show that the combined simulation results of the modified coalescence model proposed based on the mesoscale and the breakup model considering viscous shear are in the best agreement with the experimental data, this provides a model basis for the paddle type optimization of large bioreactors. Because industrial bio-fermentation is usually carried out in large bioreactors, where the stirring paddle type is crucial to the bioreactor efficiency, this paper enlarges the 5 L aerated stirred industrial bioreactor to 400 m³ by the principle of equal terminal shearing force of the impeller on the basis of the optimal bubble aggregation and fragmentation model, and the influence of the combination of six-vertical-leaf disk turbine impellers, asymmetric parabolic impellers, Blumarkin impellers and six straight-blade disk turbine impellers on the bubble breaking capacity and gas dispersion effect were discussed. The optimal model combination is further used to optimize the stirring paddle type of a 400 m³ large-scale industrial bioreactor, meanwhile, the optimal combination of 400 m³ aeration-stirred bioreactor is obtained by comprehensively comparing multiple parameters such as gas holdup and volumetric mass transfer coefficient.

There exists typical mesoscale structure of particle clusters in riser reactor, and its distribution characteristics have important impacts on gas-solid flow and reaction characteristics. The analysis of the influence of mesoscale structure is helpful to provide basic information for reactor design and optimal operation. In this paper, the gas-solid flow model in the riser is established by using the drag model based on the energy-minimization multi-scale (EMMS) method, and the influence of particle cluster on the momentum transfer between gas and solid is therefore described. In addition, by considering the existence of particle clusters and the influence of the heterogeneity of particle clusters on the chemical reaction, a correction factor describing the influence of mesoscale structure on the reaction rate is proposed, which is coupled with the gas-solid flow model. A combined flow-reaction mathematical model based on mesoscale structure is therefore established. The model is validated against the experimental data. The model was further applied to simulate and analyze the flow-reaction characteristics of an industrial catalytic cracking riser reactor. The results show that the model can reasonably describe the gas-solid interaction in the riser and can predict the distribution characteristics of mesoscale structures near the wall. Due to the existence of clusters, it is difficult for the heavy oil components to fully contact with the catalyst. The distribution characteristics of clusters can lead to the high concentration of heavy oil and low concentration of gasoline and diesel near the wall. Due to the flow resistance in the cluster, excessive secondary reactions of gasoline and diesel occur in the cluster to produce more coke, resulting in higher coke concentration near the wall. Compared with the traditional model based on averaging method, the optimal value of gasoline yield predicted by the present model is closer to the industrial practice. Therefore, the present model can reasonably describe the coupled flow-reaction characteristics in the riser, reveal the influence of mesoscale structure, and is promising in providing important basic information for the development of reaction terminator technology in industrial risers.

The flow of fuel element spheres in the pebble-bed high temperature reactor (HTR) is a typical granular flow. A mixed flow including mass flow and funnel flow can be found during HTR operation. Particle scale dynamics and mesoscale dynamics control the flow states and their transitions. In this work, we focus on analyzing the effects of particle translation, rotation and other dynamic quantities in physical model of the silo flow. We firstly carried out the experimental measurement of the rheological process of the silo particle, and used the discrete element method based on the Hertz-Mindlin and RVD (relative velocity dependent) rolling friction contact model. The kinetic quantities of spherical particles in the rheological process of particles in a conical silo were studied. Further, based on the analysis of DEM calculation results, it is found that the silo presents a mixed flow state of transition from mass flow to funnel flow from top to bottom. In the different flow pattern regions of the silo mixed flow, the correlation between the translational speed and the rotational speed is opposite; the regions with larger relative tangential motion between particles are concentrated in the funnel flow region and the side wall region. Understanding the dynamics of particles during silo rheology can help optimize silo particle flow and reduce particle surface wear.

The behavior of volatile radicals is very important for regulating coal pyrolysis tar products, but it is difficult to obtain their chemical reactions directly by experimental methods. In this paper, two dominant mechanisms of stabilization of volatile radicals and condensation reactions in bituminous coal pyrolysis associated with volatile radicals were investigated by using the large-scale ReaxFF MD simulation combining with high-performance computing and cheminformatics based reaction analysis method. The number evolving trends for the competition of stabilization and condensation reactions with time under different temperature condition were obtained with the aid of the multilevel searching strategy. The results show that stabilization reactions of volatile radicals are dominant at relatively low temperature of primary pyrolysis stage while condensation reactions of volatile radicals dominate the late pyrolysis stage at high temperature. The compromise phenomenon in competition between stabilization and condensation reactions is observed when the temperature is a little higher than that of the stage transition from the primary pyrolysis to secondary pyrolysis. Importantly, the transition point from stabilization dominant stage to the intensive competition stage of stabilization and condensation corresponds to the highest yield of tar products, while the transition point from the intensive competition stage to condensation dominant stage corresponds to the starting point for char generation. The phenomenon indicates that such understanding of reaction competitions would be very helpful to modulate tar composition and obtain the high yield of tar products industrially.

With the continuous increase of domestic polyolefin production, the competition in the polyolefin general material market has intensified, and it is very important to develop new high-performance polyolefin products. Aiming at the construction of the cloudy gas-liquid fluidized bed ethylene polymerization process and the development of high-performance polyethylene, the polymerization conditions were determined and the liquid feeding system was optimized on the basis of experiments and theoretical analysis of mesoscale structures in the gas-liquid fluidized bed. Furthermore, the cloudy gas-liquid fluidized bed polymerization process is developed and industrial tests were carried out. The molecular chain structure of the industrial products proved that the cloudy gas-liquid fluidized bed polymerization process is a novel and successful way to produce high-performance polyethylene products.

In the mesoscale perovskite material system, perovskite magic sized clusters (PMSCs) have great development prospects and application potential in the field of emerging optoelectronic devices due to their excellent semiconductor properties, such as narrow emission spectral band, high color purity, precise wavelength tunability, uniform particle size distribution, simple solution processing and synthesis process. However, the mesoscale PMSCs are easy to generate perovskite quantum dots (PQDs) with large size during the synthesis process, which is difficult to meet the needs of practical applications. To solve this problem, a simple and controllable ligand-assisted reprecipitation (LAPR) method was used to synthesize inorganic hybrid mesoscale perovskite materials of CsPbBr₃ PMSCs, CsPbBr₃ PMSCs/CsPbBr₃ PQDs mixtures and CsPbBr₃ PQDs with different luminescence properties by adjusting the ratio of valeric acid (VA) to oleylamine (OAm) surface ligands. The optical properties, morphological structure, stability and mesoscale structure evolution mechanism of the PQDs and PMSCs were studied and analyzed in detail. It is found that the ratio of surface synergistic passivation ligands VA to OAm is the key to whether the reaction can generate pure-phase CsPbBr₃ PMSCs. Moreover, when the surface passivation effect of VA and OAm ligands is optimal, it is easier to generate mesoscale pure-phase CsPbBr₃ PMSCs with excellent luminescence properties.