Solid Flow Research Articles

Improving Cleaning Performance of Rice Combine Harvesters by DEM–CFD Coupling Technology

The cleaning device is an important part of combine harvesters, as its superior or inferior performance directly affects the performance of the combine harvester greatly. With an increasing rice yield, the current single-duct cleaning performance declines greatly, and causes a large grain sieve loss level and a direct grain loss for the farms. To optimize the existing single-duct cleaning device to meet the large feeding rate requirement, firstly, the terminal velocity of rice grain and MOG (material other than grain) for different varieties was experimentally measured by the custom-made device. The effects of the moisture content of rice grains and the length of short straws on terminal velocity were studied in detail. Then, the gas–solid two-phase flow theory was comprehensively applied by utilizing the discrete element method (DEM) and computational fluid dynamics (CFD) to study the working mechanism of the existing single-duct cleaning unit, and the cleaning performance was evaluated from the view of the motion law of the threshing output within the cleaning shoe. At last, a multi-duct cleaning device was put forward, and a field experiment was performed to assess the performance of the newly developed cleaning device. The results showed that the grain sieve losses ratio and grain impurity ratio improved dramatically, proving that structure optimization of the cleaning device was feasible.

Impact of Particle Size Polydispersity on Chemical Looping Combustion of Biomass under a Continuous Injection Mode

Particle size polydispersity considerably influences the chemical looping combustion (CLC) of solid fuels. In the present work, a three-dimensional multiphase particle-in-cell (MP-PIC) method was established and applied to study the full-loop CLC of biomass under a continuous injection mode. After model validation, the gas–solid flow characteristics, solid circulation rate (SCR), particle mixing in a fuel reactor (FR), and biomass leakage at different oxygen carrier (OC) particle size distribution (PSD) widths and biomass densities were systematically explored. The results showed that OC particles significantly stratified within the FR and both loop seals. Moreover, the fluctuation amplitude of the SCR decreased as the OC PSD width increased. Small biomass particles were more likely to leak. The number fraction of total leaked biomass particles first decreased and then increased as the OC PSD width increased. In the FR, small OC particles were primarily distributed in the upper part of the bed, and large particles were mainly distributed in the lower part. In addition, within the test range, the magnitude of the density difference between biomass and OC particles positively correlated with the likelihood of biomass leaking. These observations are all beneficial for the design and optimization of the CLC process of biomass.

Numerical prediction of solid particle erosion in angle-cutting elbows with gas–solid flow

Angle-cutting elbows (ACEs) are important components of pipelines for fluid diversion and distribution. Severe erosion may occur on the internal walls of ACEs used to transport solid–gas/liquid flow. Erosion may cause pipeline failures. Therefore, the ACE erosion is a fundamental problem. However, the literature on the erosion characteristics and structural optimization of ACEs is rarely reported. This study conducts a numerical prediction of solid particle erosion in ACEs with gas–solid flow. Simulation models based on the two-way coupled Eulerian–Lagrangian approach and the E/CRC model are combined with particle-wall rebound models and a user defined function in the dispersed phase model. Simulation results are verified through a comparison with previously reported experimental results. The findings show that serious erosion occurs in the downstream part of the concave wall of ACE, whereas only slight erosion occurs on the convex wall of ACE. Therefore, anti-erosion measures should be adopted for the concave wall of ACEs. In addition, structural optimization of ACEs for erosion reduction is conducted. The optimal cutting angle is 40° > 50°, and the optimal non-dimensional cutting length is <1.05. The influence of fluid parameters on erosion characteristics is also determined. The erosion rate on the concave wall increases linearly with particle diameter and exponentially with inlet velocity.

Stress-strain state of coal wells Karaganda basin

The article considers the problem of determining the thermoelastic stresses that arise when drilling a coal seam with a depth of at least 800 m. The stress-strain state is a term that has penetrated from the mechanics of a deformable solid body into various areas, both natural and technological. Usually, three types of stress-strain state are distinguished: the first type of elastic work - up to 35% of the breaking load; the second type of elastic-plastic work - up to 75% of the breaking load, while cracks appear and their number increases with increasing load; the third type of destruction - cracks appear like an avalanche and every detail is destroyed. For the first time, we succeeded in solving analytically the Stefan problem for a cylinder of finite dimensions, with a moving interface, by selecting an integral transformation. A similar solution for a well in coal seams (as well as for other applications) gives an analytical solution to the deformation-wave process in a rock mass, discovered experimentally in the late 70s of the last century (scientific discovery of 1985, priority of 1978). Our experimental and theoretical results fit into the model of macroscopic localization of plastic flow. This model shows that the localization of plastic flow in solids (and in a coal seam) has a pronounced wave character. At the same time, at the stages of easy slip, linear and parabolic strain hardening, as well as at the stage of preliminary destruction, the observed patterns of localization are different types of wave processes.

An improved lattice Boltzmann model for fluid–fluid–solid flows with high viscosity ratio

In this paper, we present an improved lattice Boltzmann model for fluid–fluid–solid (FFS) flows with a high viscosity ratio. The bounce-back particle model is combined with the Shan–Chen (SC) multicomponent model. We extend the bounce-back scheme based on velocity interpolation and a fresh-node initialization approach with second-order accuracy to moving particles within the framework of the multicomponent model. An improved virtual solid density model for wetting boundary conditions is employed to implement contact angles on curved boundaries. We examine the factors that lead to the violation of mass conservation, and an easy redistributing method is developed to fix the mass leakage issue. The combined multiphase particle model is able to simulate FFS flows with a high viscosity ratio of up to 1000 while preserving the total mass of the two fluids. The performance of the approach is tested by a variety of numerical experiments. The dynamic behaviors of moving contact lines on the curved boundary are validated by a droplet wetting on a solid particle. The model is then applied to simulate dynamic FFS problems, such as particle wetting at the fluid interface and particle motion through a fluid–fluid interface. According to the simulation results, the present model is capable of capturing the total force exerted on a particle by the fluid and the interface. However, the SC-type fluid–solid interaction force does not equal the capillary force in the present model. Finally, the self-assembly process of two floating particles on a liquid–liquid interface is investigated.

Theoretical and numerical analysis of drag force at the interface between the dilute and dense phases

Resolving the sharp interface between the dilute and dense phases in gas–solid flows is a bottleneck in fine-grid simulations. This study addresses this issue through the theoretical analysis of an infinite gas–structure interface with arbitrary flow directions. The drag force at the interface is decomposed into three parts: the homogeneous drag forces of the dilute and dense regions and a stress divergence difference term. All the three parts are expressed as the functions of the solid volume fractions, particle Reynolds numbers, and stress divergences of the interface grid and its adjacent grids. The developed theoretical drag models at the interface are verified and improved based on particle-resolved direct numerical simulations (PR-DNSs) of flows past plug-like structures. The models are then tested against PR-DNSs of flows past bubble-containing, spherical, ellipsoidal structures. They yield significantly better performance than the traditional Beetstra et al.'s model [Beetstra et al., “Drag force of intermediate Reynolds number flow past mono- and bidisperse arrays of spheres,” AIChE J. 53(2), 489–501 (2007)].

Erosion Behaviors of Gas–Solid Flow on an Assignment Plate using CFD–DEM

The erosion wear of a gas–solid flow is a major challenge for an S Zorb reactor; it affects the production safety and stability. This study aims to investigate the erosion wear problem of a gas–solid flow on an assignment plate in an S Zorb reactor using CFD–DEM. The erosion wear behavior of the assignment plate is studied through flow field and particle trajectory analyses. Moreover, five polyhedral particle models were established by DEM to study the effect of particle shape on erosion behavior. The numerical calculation results show that the special structure of the bubble cap affords a special serrated erosion wear area. According to the movement process of particles, the erosion wear of the assignment plate is divided into two stages: first a large range of slight erosion wear occurs and then seriously concentrated erosion wear occurs. With the decrease of particle sphericity φ, the erosion wear rate first decreases rapidly and then increases slowly. φ=0.85 is the critical value of change, and the assignment plate has the lowest erosion wear rate. The simulation studies are helpful for reducing the erosion wear of the assignment plate and improving its service life.

Development and verification of coarse‐grain CFD‐DEM for nonspherical particles in a gas–solid fluidized bed

AbstractComputational fluid dynamics coupled with discrete element method (CFD‐DEM) has been widely used to understand the complicated fundamentals inside gas–solid fluidized beds. To realize large‐scale simulations, CFD‐DEM integrated with coarse‐grain model (CG CFD‐DEM) provides a feasible solution, and has led to a recent upsurge of interest. However, when dealing with large‐scale simulations involving irregular‐shaped particles such as biomass particles featuring elongated shapes, current CG models cannot function as normal because they are all developed for spherical particles. To address this issue, a CG CFD‐DEM for nonspherical particles is proposed in this study, and the morphology of particles is characterized by the super‐ellipsoid model. The effectiveness and accuracy of CG CFD‐DEM for nonspherical particles are comprehensively evaluated by comparing the hydrodynamic behaviors with the results predicted by traditional CFD‐DEM in a gas–solid fluidized bed. It is demonstrated that the proposed model can accurately model gas–solid flow containing nonspherical particles, merely the particle dynamics are somewhat lost due to the scaleup of particle size. Finally, the calculation efficiency of CG CFD‐DEM is assessed, and the results show that CG CFD‐DEM can largely reduce computational costs mainly by improving the calculation efficiency of DEM. In general, the proposed CG CFD‐DEM for nonspherical particles strikes a good balance between efficiency and accuracy, and has shown its prospect as a high‐efficiency alternative to traditional CFD‐DEM for engineering applications involving nonspherical particles.

Assessment of kinetic theory for gas–solid flows using discrete particle method

Kinetic theory is a common choice for closing the solid phase stress in the continuum theory for dilute and moderate dense gas–solid flows. In this article, methods are proposed for postprocessing the data obtained from discrete particle simulations, and the results are then used to critically assess the fundamental assumptions of kinetic theory. It is shown that (i) the fundamental assumptions and predictions of kinetic theory are, respectively, valid and accurate in homogeneous granular flows, as expected. Those results prove that the methods for data postprocessing are effective; (ii) in the case of nonequilibrium and heterogeneous gas–solid flows, nearly all fundamental assumptions get challenged, and the predictions of kinetic theory, in terms of collision frequency and particle pressure, deviate significantly from the statistical results of discrete particle simulation. Therefore, the standard kinetic theory is insufficient to provide the constitutive laws for continuum modeling of heterogeneous gas–solid flows.

Local solids flow structure in a countercurrent liquid-upward and solids-downward fluidized bed (CCLSFB) system

The local solids holdup and local particle velocity in a Countercurrent Liquid-upward and Solids-downward Fluidized Bed (CCLSFB) were investigated in details using optical fiber probes with two different models in a Plexiglas column of 1.5 m in height and 7.0 cm in inner diameter. A new flow regime map including fluidized bed, transition, and flooding regimes was established. The axial solids holdup distribution is almost uniform at low liquid velocity and/or solids flowrate and becomes less uniform with higher solids holdup at the top of the column after the operating liquid velocity is reaching the flooding velocity. The radial solids holdup profile is also nearly flat with a slightly lower solids holdup in the near-wall region at low liquid velocity and solids flowrate but becomes nonuniform as the operating liquid velocity approaches the flooding velocity. Two equations were also proposed to correlate radial local solids holdups. The descending particle velocity in CCLSFB increases with the decrease of the liquid velocity and the increase of the solids flowrate. A generally uniform particle velocity distribution was found in the axial direction, as well as in the radial direction except for a small decrease near the wall. These results on the local solids flow structure would provide basic information and theoretical supports for the design and industrial application of CCLSFB.

Hazard Zonation and Risk Assessment of a Debris Flow under Different Rainfall Condition in Wudu District, Gansu Province, Northwest China

Debris flows induced by heavy rainfall are a major threat in Northwest and Southwest China, due to its abrupt occurrence and long runout. In light of this, this work presents the runout simulation and risk assessment of the Boshuigou debris flow under different rainfall conditions in Wudu district, Gansu Province, Northwest China. Based on field reconnaissance, the geomorphological feature and main source of the Boshuigou debris flow were described. With the application of the FLO-2D simulation, the potential flow depth and flow extent of the Boshuigou debris flow under 100-year return-period rainfall and 50-year return-period rainfall were calculated. The maximum flow velocities of the Boshuigou debris flow under the 100-year return-period rainfall and 50-year return-period rainfall were 5.46 and 5.18 m/s, respectively. Accordingly, the maximum flow depths were 5.85 and 5.57 m. Then, the hazard zonation was conducted in combination of the construction and other properties within the potential impact zone, and the risk assessment of the Boshuigou debris flow under the 100-year return-period rainfall and 50-year return-period rainfall was finally completed. This work presents a method for debris flow risk assessment considering the solid source and water flow, which can provide a basic reference for mitigation and reduction of geohazards induced by torrential rainfall.

Comparison of Axial Flow and Swirling Flow on Particle Pickup in Horizontal Pneumatic Conveying

Pneumatic conveying is widely used in coal mining. As the lowest conveying velocity of materials, the pickup velocity is the key to the study of gas–solid two-phase flow. In this study, the pickup velocity of pebble particles was experimentally investigated. When the particle size is 3–9 mm, the airflow velocity was found to suitably describe the results as a function of the pickup velocity and have a high correlation. When the swirl number is 0.2, the optimal swirl number was found for which the highest particle pickup ratio was observed. Based on four different methods, namely, visual observation, mass weighing, coefficient of difference analysis, and determination of the peak-average ratio of the pressure drop in the flow field to measure the pickup velocity of the spraying material, the results showed that the accuracy of the particle pickup velocity obtained through visual observation was the lowest, and when the mass–loss rate of the particle was selected as the measurement index of the pickup velocity, the accuracy was the highest. The results will help to realize the long-distance transportation of spraying materials in inclined roadway under the shaft.

Visualization experiments and seepage characteristics of water–solid mixture flow through a rough fracture of silty mudstone under low hydraulic head

Visualization experiments and seepage characteristics of water–solid mixture flow through a rough fracture of silty mudstone under low hydraulic head

Comparative study of the single and double specularity coefficients on two-fluid modeling of a pseudo-2D gas–solid fluidized bed

The specularity coefficient is an unmeasurable parameter in the most popular wall boundary model during the two-fluid modeling of dense gas–solid flows. Using multiphaseEulerFoam solver, the influence of different specularity coefficient setting strategies on the gas–solid flow inside a pseudo-2D fluidized bed has been explored. It is found that the single specularity coefficient plays a regulatory role in the quantitative prediction. Increasing the specularity coefficient would cause a fluidization transition from freely bubbling to slugging, and the bed characteristics such as pressure drop and bed expansion present monotonic nonlinear changes. The double specularity coefficients approach is shown to significantly improve the predictive accuracy through verifying with the measured particle velocities, bubble diameter and rise velocity. In addition, the lognormal bubble size distribution and Gaussian bubble rise velocity distribution are observed. The specularity coefficient for walls in thickness direction is crucial and its different effects are unignorable. Overall, the present study provides a practical strategy of double specularity coefficients for the solid wall boundary conditions during two-fluid modeling.

Research on casing erosion in reservoir section of gas storage wells based on Gas-solid Two-phase flow

Gas storage wells are characterized by large injection and production volumes and multi-cycle high-intensity cyclic injection and production, and the high-speed flowing sand particles have a strong erosion effect on the tubular column, threatening the safety of the gas storage wells' tubular column. In this paper, gas–solid two-phase flow erosion experiments and erosion simulation are used to study the effects of sand parameters, casing materials, and formation temperature on the erosion rate of reservoir section casing during gas recovery. The results show that due to the high temperature weakening the material strength of the casing in the reservoir section, the erosion rates of N80 and P110 casings increase with the growth of environment temperature. The casing erosion rate in the reservoir section increases with the raising of gas production volume, and the casing erosion rate increases rapidly when the gas production volume of the case well exceeds 162 × 104m3/d. The increases in sand particle diameter and mass flow rate also aggravate the casing erosion. The borehole dog-leg degree affects the erosion rate of the casing by influencing the attack angle of sand particles on the casing, and the erosion rate increases significantly when the borehole dog-leg degree exceeds 3°. The study results provide theoretical guidance for the building and operation of gas storage wells and are of great practical significance.

Development of a reduced-order model for large-scale Eulerian–Lagrangian simulations

Multiphase flows with solid particles are commonly encountered in various industries. The CFD–DEM method is extensively used to simulate their dynamical behavior. However, the application of the CFD–DEM method to simulate industrial-scale powder processes unavoidably leads to huge computational costs. With the aim of overcoming this issue, we propose a nonintrusive reduced-order model for Eulerian–Lagrangian simulations (ROM-EL) to efficiently reproduce gas–solid flow in fluidized beds. In the model, a Lanczos based proper orthogonal decomposition (LPOD) is newly employed to efficiently generate a set of POD bases. After the numerical snapshots are projected onto the reduced space spanned by the POD bases, a series of multidimensional functions of POD coefficients are constructed using a surrogate interpolation method. To demonstrate the effectiveness of this model, validation studies are performed based on the simulations of a fluidized bed. The macroscopic properties, such as the particle distribution, bed height, pressure drop, and distribution of bubble size, are shown to agree well in the CFD–DEM model and ROM-EL. Further, our proposed ROM-EL reduces the computational cost by several orders of magnitude compared with the CFD–DEM simulation. Accordingly, the ROM-EL could significantly contribute to the progress of modeling and simulation for industrial granular flows.

Investigation on the internal and external solid flow rates in large-scale circulating fluidized bed with different layouts of suspended heating surfaces

Suspended Heating Surfaces (SHSs) in large-scale circulating fluidized bed (CFB) boilers have a significant impact on internal ( G s,i ) and external ( G s,o ) circulating solid flow rates that is important for heat transfer. In this paper, the distribution of G s,i and G s,o in a 650 × 680 × 3500 mm 3 CFB apparatus was simulated and verified by experimentations. On this foundation, the effects of SHSs structural layouts on G s,i and G s,o were investigated in a 350 MW supercritical CFB boiler. Results showed that G s,i increased by 65.8% as SHSs number increased from 0 to 20, whereas G s,o decreased by 17.8%, so G s,o / G s,i decreased correspondingly. Meanwhile, increasing SHSs height had a greater improvement on G s,i than width, which would be more conducive to the heat transfer near SHSs. Finally, empirical formulas of G s,o , G s,i and layout parameters of SHSs were developed, and the research results can provide meaningful reference for the operation optimization of large-scale CFB boilers. • Effects of suspended heating surface layout on circulating flow rates are studied. • The ratio variation of internal and external circulating flow rates is explored. • Internal circulating flow rate increases with increasing surface number and area. • Empirical formula of structural parameters on circulating flow rate is achieved.

Solid Medical Waste Management of Hazardous and Toxic at UNS Hospital Surakarta

In the era of the COVID-19 Pandemic, medical waste is increasing in various hospitals, including UNS Hospital. The variables studied in the hazardous and toxic solid medical waste flow treatment. Primary data was obtained from an analysis of waste amount in 2021 and interviews with incinerator managers. Secondary data in the form of waste types, impacts, and incinerator residue were obtained from the literature study. This research aims to identify solid medical waste management with hazardous and toxic materials compared with Regulation of Environment and Forestry Minister of Republic Indonesia 56/2015. After analysis, it was found that there is dangerous and harmful solid medical waste flow management, distinguished by type. Particular colored medical waste is managed by reducing, sorting, storing, transporting, and destroying. Destruction is conducted with an incinerator. Arah Environmental Indonesia Company operates infectious medical waste. The potential impact of that waste can attack health, damage the environment quality, increase the degradation that has occurred, and pose a threat to microplastic. Completing waste management is done by tightening hospital regulations to produce output according to quality standards, limiting hazardous and toxic waste use, and selecting the waste.

Modelling the minimally fluidized state under reduced pressure

Several aspects of numerically modelling a minimally fluidized gas–solid system have been investigated in this work. The numerical results show that voidage and the resulting pressure drop are not a function of the fluidizing cycle. More interestingly, the pressure drop was not impacted by introducing the lateral axis of gas and solid flow in the 3D models. Under a reduced pressure environment, none of the well-known drag models could capture the effect of the slip flow. A relatively new but not well-known slip flow drag model showed the ability to capture the impact of the slip flow regime. However, improvements in its overall accuracy are desirable. To this extent, the Ergun pressure drop equation was modified to introduce the effect of the slip flow regime. The losses in the slip flow regime were captured by deriving a new correlation using experimental work that predicted a linear relationship between the laminar coefficient and the Knudsen number. The modified Ergun equation showed notable improvement in its pressure drop accuracy. Furthermore, the modified Ergun equation was implemented as a modified Gidaspow drag model. It showed better accuracy in predicting pressure drop and minimum fluidization velocity at reduced pressure for various alumina particle sizes.

Evaluation on Micromixing of a Continuous Solid Particle Flow in In-Line HSMs by Experiments and Artificial Intelligence Approaches

Evaluation on Micromixing of a Continuous Solid Particle Flow in In-Line HSMs by Experiments and Artificial Intelligence Approaches