Heat transfer modelling in Discrete Element Method (DEM)-based simulations of thermal processes: Theory and model development

Particle-scale study of heat and mass transfer in a bubbling fluidised bed

Computational analysis of shock-induced flow through stationary particle clouds

Qualitative and quantitative characterisation for explosion severity and gaseous–solid residues during methane–coal particle hybrid explosions: An approach to estimating the safety degree for underground coal mines

Two-dimensional (2-D) numerical simulations based on the Eulerian–Lagrangian method that take droplet break-up into account are conducted to clarify the mean structure of gaseous detonation laden with a dilute water spray. The premixed mixture is a slightly diluted stoichiometric hydrogen–oxygen mixture at low pressure. The simulated results are analysed via 2-D flow fields and statistical Favre spatiotemporal averaging techniques. Gaseous detonation with water droplets (WD) propagates stably with a velocity decrease compared with the dry Chapman–Jouguet speed. The mean structure of gaseous detonation with dilute water spray shares a similar structure as the one without water spray. However, the hydrodynamic thickness is changed due to the interaction with water spray. Overall interphase exchanges (mass, momentum and energy) that take place within the hydrodynamic thickness induce a decrease of the detonation velocity and lower the level of fluctuations downstream of the mean leading shock wave. Droplet break-up occurs downstream of the induction zone and in our case, the water vapour from the evaporation of water spray does not affect the reactivity of gaseous detonation. The laminar master equation for gaseous detonation laden with inert WD shows that the hydrodynamic thickness should rely on the gaseous sound speed, and works well as the working mixture is weakly unstable and its cellular structure is regular. The droplet flow regimes and break-up modes have also been determined. The characteristic lengths of detonation and interphase exchanges have been ordered under the present simulation conditions and have been shown to be intimately intertwined.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022112019010188

Numerical analysis of the mean structure of gaseous detonation with dilute water spray

We used the computational fluid dynamics–discrete element method (CFD–DEM) model of compressible flow to numerically investigate the flame structure during shock-wave-induced layered coal-dust combustion, which poses a significant risk in coal mines. This represents the first attempt to apply a CFD–DEM model to compressible reactive gas–particle flow. The Eulerian–Lagrangian model for compressible gas–particle flow was extended to simulate shock–particle interactions in a reactive flow field. The particle interactions were predicted by the DEM, and source terms for homogeneous and heterogeneous reactions were included in the governing equations. The calculations were validated for inert particle dispersion from shock–particle interactions and flame propagation velocity in layered coal-dust combustion. The results were consistent with those from previous experiments. Furthermore, the flame structure in layered coal-dust combustion was revealed using the CFD–DEM approach. The simulation of the layered coal-dust combustion indicated that the shock wave was initially generated by gas detonation in a narrow channel with coal-dust particles at the bottom. The predicted propagation mechanism during layered coal-dust combustion was consistent with that reported in a previous numerical study based on the Eulerian–Eulerian approach (Hoium et al., 2015). Moreover, the flame comprised a leading shock wave and diffusion flame; the coal-dust particles were dispersed and heated by the shock wave and combustion products, respectively. The diffusion flame structure propagated at 350–500 m/s, resulting in devolatilization behind the reaction front. However, the CFD–DEM results indicated that the particle dispersion heights were higher than those predicted by the Eulerian–Eulerian approach (despite similarities in the inert particle dispersion results of these methods), attenuating the compression wave from the reaction front and slowing the leading shock wave.

Using an extended CFD–DEM for the two-dimensional simulation of shock-induced layered coal-dust combustion in a narrow channel

A two-dimensional numerical simulation of the interaction between a shock wave and a particle cloud curtain (PCC) in a shock tube was conducted to develop the numerical method and to understand how the particle layer mitigates the shock wave. In the present study, computational fluid dynamics/the discrete element method in conjunction with drag force and convective heat transfer models were used to separately solve the continuum fluid and particle dynamics. The applicability of the method to the gas flow and particles was validated through comparison with gas–particle shock-tube experiments, in which the PCC was generated by free fall, and particles initially had a gradient of its volume fraction and falling velocity in height. When the incident shock wave interacted with the PCC, it was reflected from and transmitted through the PCC. The transmitted shock wave had a curved front because the initial gradient in the volume fraction of particles locally changed the interaction between the shock wave and the particles. We calculated the effects of the drag force and heat transfer in mitigating the strength of the transmitted shock wave. The propagation of the transmitted and reflected shock waves and the motion of the PCC induced by the gas flow behind the shock wave agreed well with previous experimental data. After the interaction between the gas flow and the PCC, drag force and heat transfer were activated by the gradients in pressure, velocity, and temperature between them, and the gas flow lost momentum and energy, which weakened the transmitted shock wave. At the same time, the PCC gained momentum and energy and was dispersed. The contact forces between two particles affected the local dispersion of the PCC.

Numerical investigation of the interaction between a shock wave and a particle cloud curtain using a CFD–DEM model

This paper conducts a numerical study of particle dispersion by vertical shock waves using a combination of computational fluid dynamics and the discrete element method (DEM) The Magnus force is important for particle dispersion, and the DEM approach can consider the rotation of individual particles and provide a detailed analysis of particle–particle and particle–wall interactions Simulations are conducted and the results are compared with those of previous experiments, showing that the models can capture the particle dispersion process and shock wave geometry inside the mixed gas–particle region During the particle dispersion process, the contact force due to the particle–particle interactions causes the particles to move upward after the shock wave passes and then decreases rapidly due to the low collision frequency in the particle cloud The Magnus force is initially lower and has little effect until the contact force decreases, when it becomes dominant and maintains the particles’ upward movement It is mainly driven by the gas rotation above the dust layer, and the effect of particle rotation is relatively small in comparison The gas velocity gradient above the dust layer in the particle dispersion region is caused by gas–particle interactions The particle dispersion region becomes wider and thinner over time, meaning that the gas velocity gradient above the dust layer becomes small and hence that the Magnus force (which is driven by the gas rotation) also becomes small In contrast, the downward drag force remains constant during the vertical motion because it is primarily affected by the velocity difference between the particles and the gas This means that the drag and Magnus forces eventually balance, and the particles stop rising

Two-dimensional CFD–DEM simulation of vertical shock wave-induced dust lifting processes

In this paper, two-dimensional CFD-DEM was conducted to investigate the effect of Magnus force for the dust dispersion by vertical shock wave. Magnus force is mainly driven by the gas rotation inside the boundary layer near the surface of dust layer, and the particle rotation generated by collisions has smaller contribution for Magnus force. The gas rotation only has large value inside the boundary layer, so that Magnus force becomes insignificant with dust lifting.

Numerical Investigation of Dust Lifting Induced by Vertical Shock Wave

Mitigation of blast wave, caused by explosion of explosives, from a straight tube using water in a bag (water bag) was evaluated. The length of the tube was 330 mm and the cross-section area was 30 x 30 mm2. One end of the tube was closed. The water bag was placed on the floor or closed end wall of the tube near the explosive. The thickness of water was 3 mm. A specially designed small detonator, which contains lead azide of 100 mg, was ignited near the closed end wall of the tube. The blast pressure outside the tube was measured and examined. The blast wave was remarkably mitigated by the water bag. Equivalent ratio analysis revealed that the glass beads absorbed 33%-45% of explosion energy.

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Kei Shimura

Papers

Using an extended CFD–DEM for the two-dimensional simulation of shock-induced layered coal-dust combustion in a narrow channel

Numerical investigation of the interaction between a shock wave and a particle cloud curtain using a CFD–DEM model

Two-dimensional CFD–DEM simulation of vertical shock wave-induced dust lifting processes

Numerical Investigation of Dust Lifting Induced by Vertical Shock Wave

Blast mitigation by water in a bag on a tunnel floor