Analysis Of Granular Flow Research Articles

Granular flow in novel Octet shape-based lattice frame material

Abstract Moving packed-bed heat exchanger in concentrated solar power (CSP) plants involves heat transfer between heated falling particles and supercritical carbon dioxide. The overall effective thermal conductivity of the moving packed bed and particle-side channel contact resistances are still the bottlenecks in achieving the desirable thermal transport levels. To this end, a novel moving packed bed heat exchanger consisting of Octet lattice packed between the walls of the particle-side channel is proposed in this study. Granular flow analysis in Octet lattice moving-packed bed heat exchanger (OLHX) was conducted through experiments and DEM-based numerical simulations. The experimental images clearly demonstrated stagnation regions upstream of lattice fibers, void regions downstream of the fiber junctions and wavy type unobstructed flow on lateral sides of the fibers. DEM simulations were successful in capturing all these critical flow phenomena. Larger flow velocities were observed on the lateral sides of the fibers in the simulations. Also, when the particles in the silo were emptied, the final images showed accumulation of particles on the inter-fiber as well as fiber-channel wall junctions. Moreover, the fiber connections resulted in some regions devoid of the particle contact on the channel endwall which means that these regions would suffer from poor thermal exchange. The overall mass flow rate increased with increasing porosity for a fixed particle diameter.

Numerical simulation of 2D granular flow entrainment using DEM

To understand the entrainment process in granular flow, numerical experiments have been conducted using a Discrete Element Method model. A flow channel of 8 m long with $$15^\circ $$ slope is setup with monitoring points located in an erodible bed. Particles, ranging from 3 to 4 mm in diameters, are used in the simulations. In the simulations, translational, rotational and average velocities, total volume, shear stresses are calculated in the measurement circles. The sizes of the measurement circles have been varied to see their effects on the results. It is found the minimum size of the measurement circles should include 20–30 particles. An new analytical model has been developed to calculate entrainment in granular flow. Results of the numerical experiment are compared with analytical model. Shear stresses at the interface between flowing particles in motion and the immobile particles in the channel bed, change of depth of erosion and entrainment rate are used to verify the analytical model. It is found that the calculated shear stresses in the PFC model agree well with the shear stresses calculated using Mohr–Coulomb frictional relationship in the analytical model. The calculated depth of erosion using the new analytical model is also compared with that from dynamic and static entrainment model. The results indicates that the analytical model is able to capture the mechanism of erosion and it can be used in granular flow analysis.

DEM/CFD analysis of granular flow in static mixers

Mixing of powders, particles and/or granules obtains an economic importance in various technologies, and in the food, pharmaceutical and chemical industries. In many cases, the mixing process greatly influences the quality of the final product. The parameters of the mixing process and the design of equipment have a strong impact on the mixing efficiency, and the quality and the price of the intermediate or final product. In this study, the discrete element method (DEM) is used for modeling of granular flow in various multiple Komax and Ross mixing applications. Computational fluid dynamic (CFD) method was used for modeling of fluid flow through the Eulerian multiphase model. Coupling of these two methods provides reliable, sufficiently correct and adequate results of the proposed model compared to experimental measurements. The objective of this paper is to predict the behavior of particles in different static mixer configurations. The results of the numerical simulation are compared with appropriate experimental results. Application of this model provides the optimization of the geometry and parameters of mixing systems taking into account the quality of the mixing process and the cost of the final product.

Unsteady granular flows in a rotating tumbler

The characteristics of steady granular flow in quasi-two-dimensional rotating tumblers have been thoroughly investigated and are fairly well understood. However, unsteady time-varying flow has not been studied in detail. The linear response of granular flow in quasi-two-dimensional rotating tumblers is presented for periodic forcing protocols via sinusoidal variation in the rotational speed of the tumbler and for step changes in rotational speed. Variations in the tumbler radius, particle size, and forcing frequency are explored. Similarities to steady flow include the fastest flow occurring at the free surface of the flowing layer and an instantaneous approximately linear velocity profile through the depth. The flowing layer depth varies by 2-5 particle diameters between minimum and maximum rotation rates. However, unsteady forcing also causes the flow to exhibit dynamic properties. For periodic rotational speeds, the phase lag of the flowing layer depth increases linearly with increasing input forcing frequency up to nearly 2.0 rad over 0-20 cycles per tumbler revolution. The amplitude responses of the velocity and shear rate show a resonance behavior unique to the system level parameters. The phase lag of all flow properties appears to be related to the number of particle contacts from the edge of the rotating tumbler. Characterization via step changes in rotational speed shows dynamic properties of overshoot (up to 35%) and rise times on the order of 0.2-0.7 s. The results suggest that the unsteady granular flow analysis may be beneficial for characterizing the "flowability" and "rheology" of granular materials based on particle size, moisture content, or other properties.

Analysis of granular flow in a pebble-bed nuclear reactor

Pebble-bed nuclear reactor technology, which is currently being revived around the world, raises fundamental questions about dense granular flow in silos. A typical reactor core is composed of graphite fuel pebbles, which drain very slowly in a continuous refueling process. Pebble flow is poorly understood and not easily accessible to experiments, and yet it has a major impact on reactor physics. To address this problem, we perform full-scale, discrete-element simulations in realistic geometries, with up to 440,000 frictional, viscoelastic 6-cm-diam spheres draining in a cylindrical vessel of diameter 3.5m and height 10 m with bottom funnels angled at 30 degrees or 60 degrees. We also simulate a bidisperse core with a dynamic central column of smaller graphite moderator pebbles and show that little mixing occurs down to a 1:2 diameter ratio. We analyze the mean velocity, diffusion and mixing, local ordering and porosity (from Voronoi volumes), the residence-time distribution, and the effects of wall friction and discuss implications for reactor design and the basic physics of granular flow.

608 チェーンコンベアにおける粒子せん断流れの解析

608 チェーンコンベアにおける粒子せん断流れの解析