Particle Flow Characteristics Research Articles

Experimental study on particle flow characteristics of three-dimensional moving bed

The disorderly treatment of blast furnace slag has caused huge energy waste. To tackle this issue, moving bed are continuously attracting worldwide attention. In this paper, the in-depth analysis of the flow characteristics of blast furnace slag-like particles in a solid-solid heat transfer moving bed is carried out. The particle flow pattern and velocity in the moving bed with different tube numbers, configurations and spacings are vividly recorded. Significantly, a quantitative formula of the mass flow rate including the opening width, the bed layer height, the tube number and spacing, the particle size and distribution was built for this solid-solid heat transfer model. Furthermore, it is found that the longitudinal velocity distribution of the particles renders obvious peaks and valleys along the width direction. This study provides theoretical guidance for the optimization of the structure and operational parameters of the solid-solid heat-exchange moving bed.

Three-dimensional CFD simulation and experimental validation of particle segregation in CFB riser

PurposeThe purpose of this paper is to perform the computational fluid dynamics (CFD) simulation with experimental validation to investigate the particle segregation effect in abrupt and smooth shapes circulating fluidized bed (CFB) risers.Design/methodology/approachThe experimental investigations were carried out in lab-scale CFB systems and the CFD simulations were performed by using commercial software BARRACUDA. Special attention was paid to investigate the gas-particle flow behavior at the top of the riser with three different superficial velocities, namely, 4, 6 and 7.7 m/s. Here, a CFD-based noble simulation approach called multi-phase particle in cell (MP-PIC) was used to investigate the effect of traditional drag models (Wen-Yu, Ergun, Wen-Yu-Ergun and Richardson-Davidson-Harrison) on particle flow characteristics in CFB riser.FindingsFindings from the experimentations revealed that the increase in gas velocity leads to decrease the mixing index inside the riser. Moreover, the solid holdup found more in abrupt riser than smooth riser at the constant gas velocity. Despite the more experimental investigations, the findings with CFD simulations revealed that the MP-PIC approach, which was combined with different drag models could be more effective for the practical (industrial) design of CFB riser. Well agreement was found between the simulation and experimental outputs. The simulation work was compared with experimental data, which shows the good agreement (<4%).Originality/valueThe experimental and simulation study performed in this research study constitutes an easy-to-use with different drag coefficient. The proposed MP-PIC model is more effective for large particles fluidized bed, which can be helpful for further research on industrial gas-particle fluidized bed reactors. This study is expected to give throughout the analysis of CFB hydrodynamics with further exploration of overall fluidization.

Computational fluid dynamic–discrete element method coupling analysis of particle transport in branched networks

An understanding of the particle transport characteristics in a branched network helps to predict the particle distribution and prevent undesired plugging in various engineering systems. Quantitative analysis of particle flow characteristics is challenging in that experiments are expensive and particle flow is difficult to detect without disturbing the flow. To overcome this difficulty, man-made fractal tree-like branched networks were built, and a coupled computational fluid dynamic and discrete element method model was applied. A series of numerical simulations was carried out to analyze the influence of fractal structure parameters of networks on the particle flow characteristics. The joint influence of inertial, shunt capacity and superposition from upstream branches on particle flow was investigated. The injection position at the inlet determined the particle velocity and its future flow path. The particle density ratio, particle size and bifurcation angle had a greater influence on the shunting of K2 branches than that in the K1 level and Nk22/Nk21 reached a maximum at 60°. Compared with a network with an even number of branches, there was a preferential branch when the branch number was odd. The preferential branch effect or asymmetry degree of the level (K2) branches had a more significant impact on particle shunting than that from the upstream branches (K1).

DEM study on the effects of pellet characteristics on particle flow in rectangular hopper

In this work, a non-cohesive and multi-element particle model of discrete element method (DEM) was constructed, which was used in combination with experiments to investigate the particle flow characteristics in retangular hopper equipped with the screw discharging machine. On this basis, different diameter pellets (dp = 20 mm, 25.02 mm) with various sphericities (φ = 0.868, 0.985, 1) and particle size distribution (a = 0:1, 0.1:0.9, 0.15:0.85, 0.2:0.8) were selected to examine the effects of sphericity and particle size distribution on the distribution of particle average velocity, motion distance and voidage. Our results showed that as the a increased, the particle average vertical velocity was first decreased and then increased. The motion distance of particles at 1/2 bed height was relatively stable. Furthermore, the average voidage of cylindrical particles was the largest and that of ellipsoidal particles was the smallest. Finally, the specific position of the lag of particle motion is revealed.

Process of particles flow across staggered tubes in moving bed

Moving beds with staggered tubes are widely used in industrial applications to heat or cool solid particles. The heat transfer process is complicated and involves heat transfer amongst particles and between particles and tubes. Furthermore, the heat transfer mechanism is directly determined by the flow characteristics of particles across the outer surfaces of tubes because particles are the main heat carriers of particle flow. However, the particle flow across tubes is a kind of non-continuum flow, which is substantially different from Newtonian fluids, and the continuum theory is inappropriate for predicting particle flow in moving bed. In addition, little attention has been focused on this process. Thus, it is necessary to study the flow patterns of particles across tubes before studying the corresponding heat transfer mechanism. To describe this process, this work establishes a quasi-funnel flow (QFF) model, which can be used to calculate parameters, such as velocity field and residence time, by analyzing particle flow characteristics. The discrete element method (DEM) is used for a numerical simulation of three-dimensional particle flow across staggered tubes. The flow patterns, velocity field, typical particle trajectories and particle flow of local areas are obtained. Meanwhile, a moving bed experimental system is constructed, and the obtained results are used to verify the DEM numerical simulation results. Lastly, the results of the QFF model and that of the validated DEM numerical simulation are compared and found to be consistent. The ranges of the parameters required to describe the particle flow across tubes and the applicable range of the QFF model are also determined.

Analysis of Gas-Solid Flow Characteristics in a Spouted Fluidized Bed Dryer by Means of Computational Particle Fluid Dynamics

In order to grasp the particle flow characteristics and energy consumption of industrial fluidized spouted beds, we conduct numerical simulations on the basis of a Computational Particle Fluid Dynamics (CPFD) approach. In particular, the traction model of Wen-Yu-Ergun is used and different inlet conditions are considered. Using a low-speed fluidizing gas, the flow state of the particles is better and the amount of particles accumulated at the bottom of the bed wall becomes smaller. For the same air intake, the energy loss of a circular nozzle is larger than that of a square nozzle.

Cold-state experimental study on discharge characteristics of solid particles in a gravity driven moving bed solar receiver

A small-scale multi-tube experimental system was established to pretest the workability of a gravity driven moving bed solar receiver with its absorbing section containing an insert in each tube. Discharge characteristics of solid particles with various particle sizes range from 149 μm to 1359 μm in mean diameter are studied at ambient temperature. In multi-tube experiments, the discharge rate in each tube is almost uniform. In single-tube experiments, the packed height in the particle dispenser exhibits negligible influence on the mass flow rate. Three models have been set up to predict the mass flow rate in the without-insert case of particle flow experiments. Among them, Model-3 is shown to obtain the minimum mean error of 1.54% compared with the experimental results, and proved that the influence of particle size and orifice diameter on the gas-solid slip velocity should be considered. Effect of the insert on particle flow characteristics was also investigated. The added insert in the tubes is proved to increase the mass flow rate of the finest particles. However, for particles coarser than 642 μm in mean diameter, this effect is insignificant and the mass flow rate in with-insert case is consistent with predicted results by Beveloo equation and Model-3. Besides, the experimental results of particles finer than 297 μm in with-insert case are larger than predicted results by Model-3 and less than that by Beveloo equation. It is noteworthy that two types of flow instability are observed with specific experimental variables, indicates that particle layer thickness, particle size and orifice diameter are relevant parameters to affect the granular flow state. Hence, optimizing structural parameters and selecting suitable size of particles are necessary to avoid flow instability in this type of solid particle solar receiver.

Study of the hydraulic transport of non-spherical particles in a pipeline based on the CFD-DEM

Slurry pipeline transport, which is widely used in dredging, is an important method of solid material transportation. The internal structure information of flows with different shaped particles must be obtained to investigate the effects of different particle shapes on the efficiency and flow characteristics of slurry transport. To solve this problem, a numerical method which couples the computational fluid dynamics (CFD) and the discrete element method (DEM) is established in this study. Using the coupled CFD-DEM, the internal flow structure for spherical, square platens and line-shaped coarse particles is studied, and the working conditions under which clogging of non-spherical particles occurs are explored. The flow states of different shaped particles at velocities of 2, 4.1 and 8 ms−1 are qualitatively analyzed in a horizontal pipeline system within the diameter of 100 mm, and quantitative analyses of the concentration distribution in different flow regimes are performed. The study describes the particle flow characteristics under clogging conditions based on the flow regime transition and concentration distribution. Abnormal transport is analyzed using qualitative and quantitative indications. In addition, along with the particle force and robustness of transport, the conditions for stable transport are discussed.

Numerical simulation of the effect of fine fraction on the flowability of powders in additive manufacturing

Additive manufacturing (AM) is a rapid and flexible technique for the production of metal parts and prototypes from metal powders. The quality of parts manufactured using AM is a strong function of powder physical and mechanical properties. Previous work has shown that powders with a large fraction of fine particles produce better parts in terms of smooth finished surface and high mass density. However, an excessive fine fraction in the source powder causes serious flowability issues, leading to unexpected voids or discontinuities in the finished product. This effect of the fine fraction on the flowability of metal powder is widely encountered but poorly understood in the AM industry. This study presents a three-dimensional (3D) discrete element method (DEM) model to simulate the microscale mechanisms of powder flow considering the effects of van der Waals force. This microscale force has a negligible influence on the flowability of coarse grains, but the effect becomes the dominant factor governing the behavior of fine fractions (micrometer scale). The results show that the numerical model presented in this paper is capable of reproducing the experimental dependency of the powder flowability on the fine fraction. Moreover, it also successfully captures the characteristics of particle flow under the influence of microscale van der Waals force.

Numerical Study of Flow and Heat Transfer in Gravity-Driven Particle Flow Around a Circular or Elliptical Tube

Gravity flowing beds of particles are widely found in chemical engineering industries, where the particle flow and heat transfer inside are very important for high efficiency and safe operations in the relevant facilities. In the present study, the particle flow around a circular or elliptical tube is numerically investigated with the discrete element method (DEM), where the particle flow and heat transfer in different zones around the tube are carefully analyzed. According to the particle flow and geometric characteristics of the tube, eight particle flow zones are established around the tube. It is found that the pore structure, contact number and velocity of particles in different particle flow zones are different due to the size of the stagnation zone and cavitation zone at the top and bottom of the tube. Compared with the circular tube, the porosity in the region of R < 2 dp outside the elliptical tube is smaller in zone 1, 3 and 4. The contact number in zones 3 and 4 are almost 1.3 and 1.5 times of that of the circular tube respectively, and the particle velocity in the stagnation zone is larger. Finally, based on the flow characteristics of particles around the two kinds of tubes, the heat transfer performance of the two kinds of tubes in different zones is analyzed. Due to the improvement of flow performance around the elliptical tube, the heat transfer performance of the elliptical tube is better than that of the circular tube.

Experimental and numerical study of a horizontal-vertical gas-solid two-phase system with self-excited oscillatory flow

To better explore the energy-saving mechanism and flow characteristics of the self-excited oscillatory flow, the experiment is performed by a new self-excited oscillatory flow generator that the 45° oblique sheet is mounted through the pipe axis in a horizontal-vertical closed pneumatic conveying system. The experimental study focuses on the optimum air-velocity and power consumption, and results shows the maximum reduction of the optimum air-velocity and the coefficient of power consumption are approximately 8.2% and 16.4%, respectively. In addition, the CFD-DEM coupled approach is first developed to investigate the interaction of gas-solid flow in terms of the gas turbulent kinetic energy and spatial particle flow characteristics. Compared with the conventional pneumatic conveying, it is found that the optimum air-velocity and power consumption are reduced by the new self-excited oscillatory flow at lower air-velocities. The numerical results show that the approximately symmetric distribution of axial velocity and the intensive tangential velocity is emerged in the self-excited oscillatory flow at upstream. Particles is efficiently dispersed and suspended by the self-exited oscillatory flow reflecting in the smaller particle variation coefficient and the lager particle suspension coefficient. And since the airflow kinetic energy is utilized more fully to promote particles flowing, the spatial particle axial velocity is accelerated and reached early steady state. As a result, the developed numerical model is further explained the mechanism of energy saving with the self-excited oscillatory flow.

Experimental and Numerical Investigation of Particle Flow and Mixing Characteristics in an Internally Circulating Fluidized Bed

Experimental and Numerical Investigation of Particle Flow and Mixing Characteristics in an Internally Circulating Fluidized Bed

Influence of inclined plates on flow characteristics of a liquid-solid fluidised bed: A CFD-DEM study

An in-depth analysis of liquid-solid flow characteristics of a modified fluidised bed equipped with inclined channels has been conducted using a coupled model of computational fluid dynamics (CFD)-discrete element method (DEM). Specifically, the simulation results have provided local information on the two phase flow characteristics of the modified fluidised bed including solid distribution, particle velocity distribution and energy dissipation rate of the liquid flow. It is shown that the strong reflux of sediments from the inclined channel into the bottom vertical section induced intensive circulations of both solid particles and the liquid phase. As a result, solid distribution over the entire bed became more non-uniform as the fluidisation velocity increased. Moreover, the subsequent impingement of the liquid-solid flow onto channel walls resulted in a much higher energy dissipation rate of the liquid flow, indicating a higher energy loss when compared to conventional fluidised beds. Also, an optimum fluidisation velocity was identified at which the solid concentration of the sediment layer reached its peak. It was shown that smaller inclination angle led to lower bed expansions and greater solid reflux, resulting in stronger two-phase flow circulations in the vertical section. For fluidised beds with multiple inclined channels, the particle flow characteristics in individual inclined channels were observed to be rather similar with smaller overall particle velocities and more compact sediments. The predicted results of the CFD-DEM model were found to be in good agreement with the experimental data and those predicted by our kinematic model, with a maximum deviation of 12%. The CFD-DEM model presented here can be utilised to optimise the design and operation of liquid fluidised beds containing inclined channels.

Modeling the effect of moisture on the flowability of a granular material

The flowability of granular materials is a crucial parameter to consider that impacts many engineering and industrial applications such as slope stability, powder handling and storage. The dependence of mechanical properties of granular materials on their water content is widely encountered but poorly understood. This paper presents a three-dimensional (3D) discrete element method model to simulate the microscale mechanisms of granular materials in terms of interactions between individual particles as well as interactions with surrounding fluid through liquid bridging. Formulation of the contact model is first introduced. Then the numerical model is validated by comparing the simulation results with experimental data reported in literature. Direct shear, repose angle and rotary drum tests are simulated with a synthetic material under various moisture contents. The effects of moisture on the shear strength and flowability are evaluated. The simulation results show that the numerical model presented in this paper is capable of reproducing the dependency of the shear strength on water content. Moreover, it also successfully captures the characteristics of particle flow under wet conditions.

Hydrodynamic Flow Characteristics in an Internally Circulating Fluidized Bed Gasifier

In this paper, the hydrodynamic flow inside an internally circulating fluidized bed (ICFBG) was characterized using experimental and three-dimensional computational fluid dynamics (CFD) models. Eulerian-Eulerian model (EEM) incorporating the kinetic theory of granular flow was implemented in order to simulate the gas–solid flow. A full-scale plexiglass cold flow experimental model was built to verify simulation results prior to the fabrication of the gasifier. Six parameters were manipulated to achieve the optimum design geometry: fluidization flow rate of the draft tube (Qdt), aeration flow rate of the annulus (Qan), initial bed static height (Hbs), draft tube height (Hdt), draft tube diameter (Ddt), and orifice diameter (Dor). The investigated parameters showed strong effect on the particle flow characteristics in terms of the pressure difference (ΔP) and solid circulation rate (Gs). The predicted results by simulation for the optimum case were in close agreement with experimental measurements with about 5% deviation. The results show that the ICFBG operated stably with the maximum Gs value of 86.6 kg/h at Qdt of 350 LPM, Qan of 150 LPM, Hbs of 280 mm, Hdt of 320 mm, Ddt of 100 mm, and Dor of 20 mm.

Experimental investigation of an internally circulating fluidized bed with 32-electrode electrical capacitance volume tomography

32-electrode electrical capacitance volume tomography (ECVT) was initially developed to investigate the inner flow characteristics of the internally circulating fluidized bed (ICFB) with baffle. The electrodes of the 32-electrode ECVT sensor were arranged based on their structure and dimension. The sensor characteristic was explored using the Finite Element Method. Additionally, a data acquisition system with 32-channel capacitance measuring units was also developed. The imaging speed of the 32-electrode ECVT system is 130 frames/s. Simultaneously, the experimental rig for the ICFB with baffle was constructed to investigate the characteristics of particle flow under different fluidizing gas velocities. The experimental results were then compared with the reported numerical simulations of ICFB.

Comparative study on the hydrodynamics and mixing characteristics of a new-type particle mixer

The characteristics of particle flow and mixing have a considerable influence on mass and heat transfer, as well as product quality. In order to further enhance the particle mixing in an internally circulating fluidized bed (ICFB), especially along the radial direction, four slots were opened on the draft tube of an ICFB mixer. Hydrodynamic characteristics were investigated by using a multi-scale computational fluid dynamics (CFD) model incorporating the EMMS drag. The prediction in terms of cross-sectionally averaged solid holdup and particle velocity were compared to experimental data for validation. Compared with a traditional ICFB mixer, the new mixer with four slots opening on the draft tube presents strong radial particle flow through the slots, and thereby provides better mixing performance. It is found that nearly 25.4% to 29.7% of gas in the draft tube bypasses and flows through the slots into the annulus. With increase in the superficial gas velocity in the draft tube from 0.3 m/s to 0.45 m/s, the total particle circulation mass flux in the new ICFB mixer increases from 4.87 kg/s to 10.86 kg/s. The mixing index reaches about 0.98 in the new ICFB mixer.

Numerical simulation on solid-liquid two-phase flow in cross fractures

This paper presents a series of numerical simulation on solid-liquid two-phase flow in cross fractures based on the Two-Fluid Model and the kinetic theory of granular flow (KTGF). First, the model is validated by previous experimental data. Second, the dimensionless controlling parameters are derived to describe the particle-laden flow in cross fractures, including the angle between the main and branch slots (bypass angle) θ, inlet particle volume fraction αs0, the ratio of particle size to branch slot width ds/wb, the Archimedes number Ar and the Reynolds number Re. Third, the effects of the dimensionless parameters are investigated. The results show that particles tend to accumulate at the intersection between the main slot and the branch slot. Larger bypass angle between the main slot and branch slot leads to less particle’s flow into the branch slot. The distance of the branch fracture from the inlet of the main fracture induces different particle-flow characteristics into the branch slot. Particle volume fraction at the stable stage increases with the decrease of ds/wb. The deposition thickness of particles increases with the increase of the inlet volume fraction and Ar number, while decreases with the increase of Re number.

Computational investigation of particle flow characteristics in pressurised dense phase pneumatic conveying systems

A new model for predicting particle flow characteristics in dense phase pneumatic conveying systems is presented. The domain of the solid phase is evenly divided by discrete grids, based upon which particle collision forces are solved. Specifically, the collision forces inside a grid are described based on the Lagrangian framework as a function of particle flow dynamics and the local solid concentration, whilst collision forces driving particles to flow amongst grids are calculated based on the Eulerian framework as the shear stress forces induced by the solid concentration gradient. The model was applied to solve the particle flow through a dense phase pneumatic conveying pipe with a 90° horizontal-to-vertical bend. Good agreements on the pressure drop through the horizontal and the bend sections were achieved between the prediction results and the experimental data. Effects of key parameters including superficial gas velocity, bend radius and particle size on the particle flow characteristics in terms of solid flow pattern, solid concentration distribution and fluctuation, and particle velocity distribution have been investigated. The results showed that the typical particle flow patterns, i.e. stratified flow, dune flow and slug flow, were sequentially observed when decreasing the superficial gas velocity or the bend radius, or increasing the particle size. The fluctuation intensity of solid concentration that is often seen as an indication of particle flow stability was substantially higher in the bend compared to those in straight sections. The model is simple yet proves efficient and capable of accurately predicting the particle flow characteristics in the dense phase pneumatic flow systems.

Experimental Investigation on Solid Particle Flow Characteristics in Particle Curtain Heat Exchanger

The particle curtain heat exchange, which is based on the rapid heat equilibrium theory of gas-solid two-phases, has attracted more and more attentions of researchers due to its flexible system arrangement, excellent heat transfer performance and real-time adjustable heating surface etc. In order to provide data for optimal design and operational control of the curtain exchanger, experiments were conducted to investigate flow characteristics of sand particles and geometry of the curtain under different conditions such as air velocity at the inlet, initial thickness of particle curtain, diameter of sand particle and mass flow rate of particles etc.