A DEM-CFD study of the effects of size distributions and packing fractions of pebbles on purge gas flow through pebble beds

To investigate the pore structure distribution and the coupled heat and moisture transfer during the drying process of the grains, this study focuses on fixed-bed corn drying with varying levels of broken kernel rate. A model of internal flow and conjugate heat and mass transfer was established for the drying process. Random packing models of whole and half corn kernels with different proportions were generated using rigid body dynamics (RBD), and the porosity, airflow distribution, and coupling of temperature and moisture transfer in fixed beds with different levels of broken kernel rate were analyzed. A fixed-bed corn drying device was developed, and the effects of broken particle contents of 0%, 10%, 20%, and 30% on drying characteristics were studied. The research findings reveal that the radial porosity in the fixed bed exhibits an oscillating distribution, with the localized porosity decreasing as the broken kernel rate increases. Increasing the broken kernel rate intensifies the curvature of the airflow paths within the fixed bed, increasing the pressure drop in the bed. The broken kernels fill the gaps between the whole kernels, improving the uniformity of the velocity distribution within the fixed bed. Under various packing models, the average discrepancy between pressure drop obtained from Particle-resolved Computational Fluid Dynamics (PRCFD) simulations with experimental remains below 15%. The increase in broken kernel rate within the fixed bed enlarges the heat transfer area, resulting in an elevation of the transient heat transfer characteristic parameters during drying. Simultaneously, the broken kernel rate increases the surface area of mass transfer, thereby enhancing the moisture transfer rate within the fixed bed. Compared to the fixed bed without broken kernels (0%), which requires 560 min to dry the corn pile to a safe moisture of 14% (d.b.), the drying time is reduced by 60 min, 100 min, and 130 min for the respective broken kernel contents of 10%, 20%, and 30%, respectively. The PRCFD method successfully simulates the processes of convective heat and mass transfer in the fluid phase and thermal and mass diffusion in the solid phase, exhibiting a strong correlation with experimental data.

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“…The equivalent diameter of the particles with different broken kernel contents is calculated using Equation ( 15) [41].…”

Section: Data Processing Methodsmentioning

confidence: 99%

Effects of the Broken Kernel on Heat and Moisture Transfer in Fixed-Bed Corn Drying Using Particle-Resolved CFD Model

et al. 2023

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“…Helium density was 0.2518 kg/m 3 , and kinetic viscosity was 3.0705 × 10 −5 kg/m•s. Owing to the fact that the inlet velocity of helium in a tritium breeder pebble bed is in the range of 0.1~0.2 m/s, the laminar flow model was selected for steady state calculations [16,18]. Inlet velocity and outlet pressure conditions were adopted in this study.…”

Section: Mesh Independencementioning

confidence: 99%

“…The results show that the temperature of purge gas will rapidly rise from 20 • C to 500 • C as the purge gas flows into the pebble bed. For the packed pebble beds with different pebble sizes and pebble properties, Choi et al [18] and Lee et al [19] examined the influence of particle size distribution and packing factor on helium flow behavior in pebble beds. The results show that the pressure drop increases not only in proportion to packing factor, but also in inverse proportion to the difference in pebble size.…”

Section: Introductionmentioning

confidence: 99%

“…In this study, the effects of fixed walls on the packing structures and flow characteristics of purge gas helium in pebble beds are investigated numerically by combining DEM and CFD methods, which results in an effective tool for simulating the heat and mass transfer in particle packed bed [15,18]. The pebble packing method based on the DEM simulation as well as the methodology of building a model, mesh-independent analysis and simulation setups based on CFD simulation are introduced in Section 2.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of Wall Effect on Packing Structures and Purge Gas Flow Characteristics in Pebble Beds for Fusion Blanket by Combining Discrete Element Method and Computational Fluid Dynamics Simulation

Gong,

Cheng,

Zhou

et al. 2024

Applied Sciences

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In a tritium-breeding blanket of a fusion reaction, helium, used as a tritium-purging gas, will purge the tritium breeder pebble beds to extract the tritium in blanket. The purge gas flow characteristics will affect the tritium extraction efficiency. The effect of the fixed wall on the pebble packing structures and purge gas flow characteristics was investigated by combining the discrete element method (DEM) and computational fluid dynamics (CFD) method. The results indicate that the fixed wall leads to a regular packing of the pebbles adjacent to the fixed wall in association with drastic fluctuations in the porosity of the pebble bed, which can affect the purge gas flow behaviors. Further analyses of helium flow behaviors show that the helium pressure in the pebble bed decreases in a linear manner along the flow direction, whereas the pressure drop gradient of helium increases gradually with an increase in the packing factor. The reduction in porosity in the pebble bed leads to a notable escalation in helium flow velocity. Concerning the direction perpendicular to the helium gas flow, the evolution of the cut-plane averaged velocity of helium is similar to that of the porosity, except in the region immediately adjacent to the wall. The pressure drop and flow characteristics obtained in this study can serve as input for the thermohydraulic analysis of the tritium blowing systems in the tritium-breeding blanket of a fusion reactor.

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“…Discrete element method -Computational fluid dynamics (DEM-CFD) is a new method to simulate two-phase flow in recent years, and firstly proposed by Tsuji [180]. The method mainly uses the DEM model to establish a parametric model of solid particle system, describes the characteristics of collision and agglomeration between particles, and combines the advantages of CFD in the treatment of gas phase flow field, which can effectively improve the calculation efficiency and precision of numerical solution [181].…”

Section: Dem-cfdmentioning

confidence: 99%

Discrete element modeling of the machining processes of brittle materials: recent development and future prospective

Jiang

Tang

et al. 2020

Int J Adv Manuf Technol

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In recent years, the discrete element method (DEM) has been used to model the bulk material, especially for the brittle materials (such as rocks, ceramics, concrete, ice, etc.) with various mechanical properties or responses by setting serials of contact properties (such as bonds) in the particle assembly. These bonds can withstand a certain amount of force and/or moment, so that the stresses executed in the bond can be used for determining the initiation and propagation of micro-crack. There are increasing evidences over the last twenty years that the DEM is becoming an effective numerical method to simulate the cracking, crushing and deformation of continuous media under external loads. The DEM has now been widely used in the field of processing and machining of rock, ceramic, concrete and other brittle materials. In this paper, the theoretical principles, formulations, contact models as well as the numerical solving processes of DEM are introduced. The applications of DEM for the machining processes of brittle and rigid materials such as ceramics are described and reviewed in detail, with future development trend also discussed.

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A DEM-CFD study of the effects of size distributions and packing fractions of pebbles on purge gas flow through pebble beds

Cited by 24 publications

References 31 publications

Effects of the Broken Kernel on Heat and Moisture Transfer in Fixed-Bed Corn Drying Using Particle-Resolved CFD Model

Effects of the Broken Kernel on Heat and Moisture Transfer in Fixed-Bed Corn Drying Using Particle-Resolved CFD Model

Investigation of Wall Effect on Packing Structures and Purge Gas Flow Characteristics in Pebble Beds for Fusion Blanket by Combining Discrete Element Method and Computational Fluid Dynamics Simulation

Discrete element modeling of the machining processes of brittle materials: recent development and future prospective

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