Collision Behavior Of Particles Research Articles

Carbon dioxide desorption behavior of potassium carbonate supported on gamma-alumina solid sorbent in wet fluidized bed under steam atmosphere

Since the carbon dioxide (CO2) capture using solid sorbent is a reversible reaction, the solid sorbent can be regenerated by the desorption process. Therefore, the desorption process is one of the key important processes for the CO2 capture system. Traditionally, most of the literature studies focus on the desorption of solid sorbent under an N2 atmosphere. However, the desorption process of the solid sorbent is inappropriate in the real system because the system will need another process to separate CO2 and nitrogen (N2) after the desorption process. This study focused on the CO2 desorption of potassium carbonate supported on gamma-alumina (K2CO3/γ-Al2O3) in a wet fluidized bed under a steam atmosphere by using the multiphase computational fluid dynamics (CFD) simulation. The effects of water thickness and dry restitution coefficient on CO2 desorption rate were investigated to provide a realistic particle collision behavior and to explore their effects on CO2 desorption phenomena. Moreover, the effect of steam velocity on the hydrodynamic behaviors of fluidization which on CO2 desorption rate was studied. The simulated results demonstrated that all the parameters, water thickness, dry restitution coefficient, and steam velocity had significantly affected system hydrodynamics and CO2 desorption rate in the wet fluidization desorption process. Furthermore, the effect of desorption temperature on CO2 desorption rate was evaluated for finding the appropriate temperature for CO2 desorption process of K2CO3/γ-Al2O3. The results showed that the appropriate desorption temperature for CO2 desorption under steam atmosphere was the temperature over 150 °C.

Analysis of the particle collision behavior in spiral jet milling

Collision behaviors of particles in spiral jet milling were analyzed by using a simulation. The motion of the particles was tracked by the discrete element method (DEM), and the air flow was represented by the computational fluid dynamics (CFD). The DEM was coupled with the CFD by a one-way coupling method. The simulated air flow was validated by comparing the fluid velocity field with the measured one in a model experiment. Furthermore, the air flow and particle behaviors in a spiral jet mill used commercially were analyzed by using the simulation. As a result, the particles with a region balancing between centrifugal and radial drag forces could be mainly ground by the high-speed collisions between the particles circulating near the top and bottom walls of the grinding chamber.

On the prediction of particle collision behavior in coarse-grained and resolved systems

The discrete element method (DEM) simulates granular processes and detects inter-particle collisions during the simulation. Detection of collision helps researchers to study the occurrence of particulate mechanisms such as aggregation, breakage, etc. DEM demands high computational costs in simulating industrial-level systems, as it involves an enormous number of particles. DEM coarse-grained model can help to overcome this high computational cost issue. However, the frequency and probability of collisions for different particle size classes may change when coarser particles are introduced. This study introduces a new mathematical formulation, namely the collision dependency function (CDF), which predicts the probability of collisions between different particle classes for systems containing resolved and coarse-grained particles. The CDF is extracted by executing one DEM simulation consisting of number-based uniformly distributed particles. Furthermore, a new optimized scheme is used inside the DEM to store the collision data efficiently. Finally, the collision probabilities between size classes obtained from DEM simulations are compared successfully against their counterparts calculated from the developed model for verification.

Collision characteristics and breakage evolution of particles in fluidizing processes

Fluidized beds are widely used in chemical reactors. Particles in fluidized bed usually circulate between reactors, and therefore, particle attrition cannot be avoided. Catalyst particle attrition in the fluidized bed significantly shortens their lifespan and raises operating costs. This study established an irregular polyhedron model of the particles to acquire their motion and force characteristics by the Euler-Lagrangian method and then employed the Ab-T10 breakage model to predict the particle's breakage process. The collision frequency and stress characteristics of the three-dimensional surface of a single particle were explored, as well as the time-dependent variations in the collision frequency and impact power between particles. The breakage and elutriation processes of a single particle were observed. The investigation found that the velocity differential between particles was the main factor that caused impact power. The particles were typically crushed one to six times before becoming completely fine powder, and their size evolution can be summarized in three stages. The complete process of particle breakage was revealed by tracing the size evolution of a single particle. This work would contribute to a deeper understanding of particle collision behavior and breakage mechanisms in fluidized beds.

Numerical Analysis of the Factors Influencing the Erosion of the Valve Port of a High-Speed On/Off Valve

Aiming at the problem of valve port erosion caused by contaminated particles, a three-dimensional prediction model of valve orifice erosion was established based on computational fluid dynamics (CFD) and erosion theory, considering the influence of the valve port eddy current on the oil flow. The discrete phase model (DPM) of fluent is used to obtain the orifice erosion location and erosion rate, and the causes of erosion of the high-speed on/off valve are analyzed. On this basis, several factors influencing valve port erosion are simulated to investigate the relationship between particle collision behavior and valve port erosion morphology under different factors, and the change rule of valve port erosion under different factors is analyzed. The results show that the high-speed on/off valve service life decreases with a larger cone angle of the spool, a larger pressure difference at the valve port, a larger proportion of large particle contaminants in the oil, a higher oil contamination level, and a larger filter aperture. In addition, the grey relational analysis method is used to clarify the pressure difference at the valve port, the particle size, and the filter aperture as the three most important factors affecting the erosion of the valve port of a high-speed on/off valve.

Particle collision behavior and heat transfer performance in a Na2SO4 circulating fluidized bed evaporator

• Time-domain statistical analysis is used to investigate particle collision behavior. • Polytetrafluoroethylene particles can enhance the heat transfer of Na 2 SO 4 solution. • Effect of operating variables on collision intensity and heat transfer are studied. • Standard deviation and enhancement factor increase with amount of added particles. • Particle collision behavior and heat transfer in Na 2 SO 4 and H 2 O are compared. The particle collision behavior and heat transfer performance are investigated to reveal the heat transfer enhancement and fouling prevention mechanism in a Na 2 SO 4 circulating fluidized bed evaporator. The particle collision signals are analyzed with standard deviation by varying the amount of added particles ε (1%–3%), circulation flow velocity u (0.37–1.78 m·s −1 ), and heat flux q (7.29–12.14 kW·m −2 ). The results show that the enhancement factor reach up to 14.6% by adding polytetrafluoroethylene particles at ε = 3%, u = 1.78 m·s −1 , and q = 7.29 kW·m −2 . Both the standard deviation of the particle collision signal and enhancement factor increase with the increase in the amount of added particles. The standard deviation increases with the increase in circulation flow velocity; however, the enhancement factor initially decreases and then increases. The standard deviation slightly decreases with the increase in heat flux at low circulation flow velocity, but initially increases and then decreases at high circulation flow velocity. The enhancement factor decreases with the increase in heat flux. The enhancement factor in Na 2 SO 4 solution is superior to that in water at high amount of added particles. The empirical correlation for heat transfer is established, and the model results agree well with the experimental data.

Directed energy deposition of metal matrix composites: Computational and experimental comparison of powder particle flow behavior

Directed energy deposition (DED) additive manufacturing of metal matrix composites (MMC) involves a mixture of metal and ceramic particles with a range of sizes, morphologies, and densities. Such a heterogeneous mixture of physical characteristics makes it difficult to establish optimum deposition conditions, and hence extensive parametric experiments are often needed to optimize the microstructure and performance of a final component. To provide insight into the behavior of metal and ceramic powders during DED, we report on a study that uses two complementary approaches. First, we formulate a 3-dimensional COMSOL numerical model to simulate the particle trajectories under the influence of gas flow, particle-gas interactions and particle-wall collisions. Second, we implement high-speed photography to examine and compare the powder flow behavior of metallic particles (Inconel 718) and ceramic particles (TiC). Our results reveal that there are distinct differences in particle velocity and spatial distribution between the Inconel 718 and TiC particles, due to the dissimilar particle sizes, morphologies, material densities, and particle collision behavior. By understanding these differences, as presented here, targeted compositions and homogeneous reinforcement distribution can be attained in DED components through proper material and process parameter selection; furthermore, the custom design of tailored microstructures for heterogenous functionality can also be achieved.

Effect of particle collision behavior on heat transfer performance in a down-flow circulating fluidized bed evaporator

The particle collision behavior is investigated to analyze the heat transfer enhancement mechanism in a down-flow circulating fluidized bed evaporator. Water and Polyformaldehyde particles are selected as working media. Collision acceleration signals at varied amount of added particles (0–2%), circulation flow rate (2.15–5.16 m3/h) and heat flux (8–16 kW/m2) are analyzed with kurtosis and power spectral density. Results show that the frequency range of particle collision is 6000–16,000 Hz. Particles provide main energy contribution in multiphase flow collisions. The generation of vapor phase obviously strengthens the collisions of other phases. With increased amount of added particles, the signal power increases, but the heat transfer enhancing factor initially increases and then decreases. Both the heat transfer enhancing factor and signal power increase with increased circulation flow rate. With increased heat flux, the signal power increases but the heat transfer enhancing factor decreases.

MD Simulation on Collision Behavior Between Nano-Scale TiO2 Particles During Vacuum Cold Spraying

Particle collision behavior influences significantly inter-nano particle bonding formation during the nano-ceramic coating deposition by vacuum cold spraying (or aerosol deposition method). In order to illuminate the collision behavior between nano-scale ceramic particles, molecular dynamic simulation was applied to explore impact process between nano-scale TiO2 particles through controlling impact velocities. Results show that the recoil efficiency of the nano-scale TiO2 particle is decreased with the increase of the impact velocity. Nano-scale TiO2 particle exhibits localized plastic deformation during collision at low velocities, while it is intensively deformed by collision at high velocities. This intensive deformation promotes the nano-particle adhesion rather than rebounding off. A relationship between the adhesion energy and the rebound energy is established for the bonding formation of the nano-scale TiO2 particle. The adhesion energy required to the bonding formation between nano-scale ceramic particles can be produced by high velocity collision.

Visualization of collision and aggregation behavior of particles simulating movement of inclusions in molten steel

Inclusions with sizes less than 1 μm in molten steel are difficult to float up to the molten steel and slag interface owing to their slow terminal velocity. Thus, increasing the size of inclusion is essential for accelerating the removal of inclusions. Polystyrene particles simulating inclusions in molten steel were quantified by direct observation of the particle collision behavior in a turbulent flow in a water model. The box-counting fractal dimension of particles was calculated by processing the binary images of aggregated particles. The fractal dimension of the outer contours of the single plastic particles was smaller than that of the aggregated particles. The fractal dimension was varied from 1.14 to 1.35. When two or more monomer particles collide, the aggregates are separated more easily, as the temperature increases from 40 to 80 °C. The aggregated particles were loose and easy to separate in the high-temperature aqueous solution. The effect of temperature on the surface tension of liquid and the interfacial tension of solid and liquid is obvious. The particles are wetting in the water solution at a temperature more than 60 °C. The relationship between the velocity of the particles and the fractal dimension of the solid particles with the equivalent diameter was discussed.

Numerical simulation of powder transport behavior in laser cladding with coaxial powder feeding

Laser cladding with coaxial powder feeding is one of the new processes applied to produce well bonding coating on the component to improve performance of its surface. In the process, the clad material is transported by the carrying gas through the coaxial nozzle, generating gas-powder flow. The powder feeding process in the coaxial laser cladding has important influence on the clad qualities. A 3D numerical model was developed to study the powder stream structure of a coaxial feeding nozzle. The predicted powder stream structure was well agreed with the experimental one. The validated model was used to explore the collision behavior of particles in the coaxial nozzle, as well as powder concentration distribution. It was found that the particle diameter and restitution coefficient greatly affect the velocity vector at outlet of nozzle due to the collisions, as well as the powder stream convergence characteristics below the nozzle. The results indicated a practical approach to optimize the powder stream for the coaxial laser cladding.

Influence of shot peening velocity on surface modification effect induced by shot peening based on analysis of particle collision behavior

Influence of shot peening velocity on surface modification effect induced by shot peening based on analysis of particle collision behavior

The effects of adhesive forces on the collision behavior of polyolefin particles

Abstract The collision behavior of particles in a polymerization reactor was simulated with the help of the Discrete Element Method (DEM). Analysis of the magnitudes of the potential forces acting on particles in a fluidized bed shows that the dominant role affecting the collision behavior of polymer particles is represented by adhesive forces causing the formation of liquid bridges and reflecting the entanglement of polymer chains. However, these forces do not act instantaneously. Therefore, the time duration of particle collisions was evaluated and subsequently compared to the characteristic times of liquid bridge formation and chain entanglement. This comparison implies that the collision lasts long enough for adhesive forces to apply. Two approaches are presented and compared which introduce these forces into the DEM algorithm. The first approach applies to any visco-elastic model (e.g. the Maxwell or Kelvin model) for force interactions between microelements from different particles; the second relies on special adhesive inter-particle connections, providing a gradual increase in adhesive force according to the corresponding dynamics. The decrease in kinetic energy of particles after collision can be evaluated by means of an experimentally measurable restitution coefficient relating the particle velocities before and after collision.

Review of some researches on nano- and submicron Brownian particle-laden turbulent flow

The study of nano- and submicron Brownian particle-laden turbulent flow has wide industrial applicability and hence has received much attention. The purpose of the present paper is to provide and review some researches in this field. The topics are related to the universality, particularity, complexity and importance of nano- and submicron Brownian particle-laden turbulent flow, the models of particle general dynamical equation, the collision behavior of particles. Finally, several open research issues are identified.

Determination of Time Duration of Polymer Particle Collision in Fluidized Bed using Discrete Element Method

AbstractDiscrete element method (DEM) is used for the investigation of the collision behavior of particles in polymerization reactor. Colliding particles in the DEM representation consist of individual mutually force interacting discrete elements, the trajectory of each of them is given by the second Newton's law of movement. The collision time was evaluated as the time period when there exists at least one force connection between discrete elements from different colliding particles. The agglomeration of polymer particles is caused by various adhesion forces (e.g. liquid-bridge force and the force reflecting entanglement of polymer chains) acting at a characteristic time scale. Characteristic time of the liquid bridge formation and of the chain entanglement was compared to the collision time obtained by simulations of collisions of polymer particles with the aim to evaluate whether this collision time is long enough for the formation of particle agglomerate.

Experimental study on the spatial distribution of particle rotation in the upper dilute zone of a cold CFB riser

Particle rotation plays an important role in gas-solid flows. This paper presents an experimental investigation on the spatial distribution of average rotation speed for glass beads in the upper dilute zone of a cold circulating fluidized bed (CFB) riser. It is shown that in the horizontal direction, the average rotation speed in the near-wall area is larger than that in the center area, while in the vertical direction, it decreases as the height increases. The reason resulting in this distribution is analyzed by considering several factors including particle size, particle shape, particle number density, particle collision behavior, and the surrounding flow field, etc. The effects of CFB operation conditions on the spatial distribution of average rotation speed are also studied. The results show that the increasing superficial gas velocity increases the average rotation speed of particles in the near wall area but takes nearly no effect on that in the center area. The external solids mass flux, however, takes the opposite effect. It is found that the average rotation speeds of particles in both areas are increased as the total amount of bed material increases.

Simulation of moving particles in 3D with the Lattice Boltzmann method

The following paper presents a way to simulate the behavior of particle agglomerates in a fluid flow by coupling the Lattice Boltzmann Method to a rigid body physics engine. By extending the basic algorithm by a fluid/particle force interaction method, the hydrodynamic forces acting on the particles can be calculated. By the use of this force interaction between the fluid and the particles and by the use of the rigid body physics engine, the movement and collision behavior of particles in a flow can be simulated. Additionally, this coupled simulation system is able to simulate the internal particle forces in the connections between sintered particles, which could break due to the forces and torques of a shear flow. This permits a prediction of possible break-ups or structural displacements.

Visualization of Collision Behavior of Particles Simulating Inclusions in a Turbulent Molten Steel Flow and Its Theoretical Analysis

The separation of inclusions with sizes less than several micrometers is very difficult due to their slow terminal velocity. Thus, increasing the volume of inclusion is essential for accelerating the removal of inclusions, and several methods for enhancing collision frequency of inclusions have been proposed, hitherto. Their collision behavior, however, has not been directly observed yet. In this study, by using a water model, the collision rate of polystyrene particles simulating inclusions in a molten steel was quantified by direct observation of the particle collision behavior in a turbulent flow. The collision rate of the particles counted by use of an image analysis method was compared with a theoretical collision rate, which was calculated by substituting the turbulent energy dissipation rate obtained in a numerical analysis into the Saffman–Turner's equation. In the range with large turbulent energy dissipation rate beyond 0.06 m2/s3, the observed collision rates deviated above the theoretical values. In view of this, the Saffman–Turner's equation has been modified so that it can be applied to the range with large turbulent energy dissipation rate.

乱流場における擬似介在物衝突挙動の可視化とその理論的考察

The separation of inclusions with sizes less than several micrometers is very difficult because the flotation speed of such small inclusions is slow. Thus, increasing the volume of inclusions is essential for accelerating the removal of inclusions, and several methods for enhancing collision frequency of inclusions have been proposed hitherto. Their collision behavior, however, has not been directly observed yet. In this study, by using a water model, the collision rate of particles was quantified by directly observing the particle collision behavior in a turbulent flow. The collision rate of particles directly counted by use of image analysis was compared with a theoretical collision rate, which was calculated by substituting the turbulent energy dissipation rate obtained in a numerical analysis into the Saffman-Turner's equation. In the range with large turbulent energy dissipation rate beyond 0.06 m 2/s 3, the observed collision rates deviated above the theoretical values. In view of this, the Saffman-Turner's equation has been modified for applying to the range with the large turbulent energy dissipation rate.

Dynamic behavior of collision of elastic spheres in viscous fluids

The dynamic behavior of the collision of two elastic spheres in a stagnant viscous fluid is investigated in this study for particle Reynolds numbers ranging from 5 to 300. The interactive behavior of these particles is examined both experimentally and theoretically. Specifically, the trajectory and velocity of a moving particle in collinear and oblique collisions with a fixed particle are measured using a high speed video system and an Infinity lens. The lattice-Boltzmann (LB) simulation is conducted to obtain the detailed three-dimensional flow field and the forces around the particles during the course of collision. Furthermore, a mechanistic model is developed which accounts for four stages of collision processes, including: (1) immediately before the collision, (2) compression during the collision, (3) rebound during the collision, and (4) immediately after the collision. The LB simulation and experimental results lead to an empirical expression for the drag force on the particle during the close-range particle–particle interaction. This close-range interaction between two approaching particles is taken into account in the equation of motion of the particle. The pressure force and added mass force are derived, based on collisions in inviscid fluids, as a function of separation distance. Results of the LB simulation and prediction by the mechanistic model are in good agreement with the experimental results. The viscous effects on the compression and rebound processes of colliding particles with regard to the elasticity properties of the particle are examined. The studies are also conducted for simulation based on a hard sphere model, which is commonly used in accounting for the particle collision behavior in gas. The study concludes that the key to proper quantification of the particle collision characteristics in liquid is the ability to accurately predict the particle velocity upon contact.