Modeling and validation of coarse-grained computational fluid dynamics–discrete element method for dense gas–solid flow simulation in a bubbling fluidized bed

Residence time distributions of different size particles in the spray zone of a Wurster fluid bed studied using DEM-CFD

To investigate the energy dissipation mechanisms within the pump and improve the computational accuracy of the solid–liquid flow numerical simulations, in this study, an improved CFD-DEM (Computational Fluid Dynamics - Discrete Element Method) method has been presented. First, the improved method of CFD-DEM is introduced, which mainly considers the turbulent dissipation of particles in the near-wall region and velocity field reconstruction. Then, the simulation results before and after the method's enhancement are compared. Finally, the analysis of the energy characteristics of the liquid phase flow field in the solid–liquid flow is conducted. Research shows that the modified CFD-DEM method significantly improves the accuracy of the particle distribution predictions, with the numerical results for head and efficiency being much closer to experimental values. In the high-speed regions of the impeller flow field, primarily located behind the pressure side of the blades, the liquid phase flow velocity and pressure fluctuations are less affected by changes in solid phase concentration. In the fluid region of the centrifugal pump, the energy loss caused by entropy production is significantly concentrated in the volute and impeller regions. Specifically, the entropy production dissipation in the volute region accounts for the substantial portion of the total entropy production, approximately 67%–68%, while the entropy production dissipation in the impeller region accounts for about 19.7%–20.4%. As the solid phase concentration increases, the energy dissipation within the pump gradually rises, and the total vorticity at the impeller inlet also increases correspondingly, with the vorticity distribution being related to the number of blades. The findings provide a reference for further exploring solid–liquid flow within centrifugal pumps.

Comprehensive investigation and comparison of TFM, DenseDPM and CFD-DEM for dense fluidized beds

CFD–DEM simulation of a pseudo-two-dimensional spouted bed comprising coarse particles

The effect of the electrostatic charge of particles was investigated in fluidized beds with conductive and nonconductive walls. For this purpose, changes in the wall surface charge density and particle contact time near the wall were examined. Computational fluid dynamics/discrete element method (CFD‐DEM) was utilized to simulate the accumulation of particle and wall‐induced electrostatic charges in a quasi‐two‐dimensional fluidized bed. Particles and walls were initially considered neutral and gained charge with time. The simulations showed that aggregated particles are formed due to the presence of the opposite electrostatic charges. Agglomerates are produced by joining the aggregated particles together. Agglomerates have a layered‐like structure and are made of positive and negative particles. Accumulation of these agglomerates and aggregated particles on the wall forms wall sheeting, which has a layered‐like structure. In other words, particles do not accumulate on the wall individually. A significant accumulation of particles near the wall was seen in the presence of electrostatic charges compared with the neutral bed. Also, the contact time of particles on the wall in the conductive case was more prolonged than in the nonconductive case. The results indicate that the CFD‐DEM approach is a helpful technique for predicting particles behaviour in the presence of the electrostatic charge.

Flow behavior of particles is simulated by means of discrete element method (DEM) in a screw conveyor. The gas flow is considered by the Euler model. The subgrid scale model turbulence model is applied to solve gas turbulence. A detailed description of the model equations applied has been presented. The comparison between computational fluid dynamics (CFD)‐DEM (i.e., considering gas flow) and DEM (i.e., not considering gas flow) simulation results is performed. Predicted mass flow rate with CFD‐DEM model is in better agreement with experiments by Roberts and Wills comparing with DEM results. The effects of incline angle and filling rate on the flow behavior of particles are predicted. The simulation results show that the gas flow has a major impact on particle flow behavior at a high rotation speed, whereas the velocity of particles increases with an increase of rotation speed. As the filling rate rises, both the translational granular temperature and the rotational granular particle temperature decline, which means that the particles fluctuation turns weak. While with an increase of incline angle, from the horizontal to vertical, the translational granular temperature is increased, but the rotational granular temperature reduces and then goes up. In brief, translational motion is a main mode of motion in a screw conveyor.

Recent studies highlight coarse-grained discrete element method (CGDEM) as a helpful tool for mitigating the computational cost associated with original discrete element method (DEM) simulations in large-scale industrial applications such as fluidized beds. This approach achieves cost savings by reducing the number of particles in the domain, while increasing their size. In the current work, CGDEM-LES (large-eddy simulation) numerical simulations are conducted on a 3D (three-dimensional) cylindrical pilot-scale fluidized bed in the bubbling regime, containing 9.6 M Geldart B-type particles. Macroscopic and mesoscopic analyses are performed, revealing qualitative and quantitative effects of coarse-graining on bed behavior. Among these effects, a global homogenization of the fluidized region is observed, marked by soaring bed surfaces, lower solid velocity, and solid fraction gradients. Additionally, a decrease in the bubble population is reported. These effects intensify as the coarse-graining factor increases. Despite influencing some results, the impact of mesh size is deemed negligible compared to that of particle coarse-graining. Some of the observed issues can be alleviated by incorporating additional mechanisms from the literature, aiming to dissipate the extra energy inherently present in coarse-grained systems. However, these mechanisms prove to be barely sufficient to replicate DEM results with the smallest coarse-graining factor tested. A thorough analysis allows identifying a side effect of one of these approaches, which is to slow particles down all the more as they move fast, causing a macroscopic misprediction of particle vertical velocity in turn. This model is then deemed less useful in the context of this study.

Fluidization is a well-established technique for processing particulate materials, characterized by intensive interactions between solid particles and the fluid flow. Among the various design parameters of fluidized bed dryers, bed height plays a critical role, directly influencing flow resistance, heat and mass transfer, and consequently, the system’s energy efficiency and overall performance. A thorough understanding of the mechanisms governing fluidized bed dynamics is therefore essential for process optimization. In this study, a three-dimensional gas-solid fluidized bed was simulated using a coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) framework. This approach enables precise tracking of particle motion and distribution, allowing the temporal evolution of bed height to be quantified. Simultaneously, flow characteristics such as gas velocity, pressure, and particle distribution were analyzed under various operating conditions. Before performing a sensitive simulation study, the model was validated against data from previously published studies, showing strong agreement with established empirical correlations and confirming the reliability of the numerical framework. Building on this validation, a parametric study was conducted to examine the effects of key operating variables - namely, inlet gas velocity and bed height - on the hydrodynamic behavior of the system. The obtained results demonstrate that these parameters have a significant impact on flow uniformity and overall bed stability.

Bubbles as mesoscale structures play an important role in the development of the inhomogeneous drag force model, which is key to the prediction of fluidized beds. A coupled computational fluid dynamics–discrete element method is employed in this work to investigate the distribution of interphase drag force around a clouded bubble in an incipiently fluidized bed. A method for the determination of the bubble boundary is proposed. The results reveal that there is a stronger positive effect of drag force around the clouded bubble because of the presence of bubble crown and wake, which is different from the cloudless bubble. The bubble-induced local inhomogeneous coefficient is also proposed to evaluate the ensemble inhomogeneous impact around the bubble.

The paper presents an extensive investigation of a small-scale sliding vane rotary expander operating with R245fa. The key novelty is in an innovative operating layout, which considers a secondary inlet downstream of the conventional inlet port. The additional intake supercharges the expander by increasing the mass of the working fluid in the working chamber during the expansion process; this makes it possible to harvest a greater power output within the same machine. The concept of supercharging is assessed in this paper through numerical computational fluid dynamics (CFD) simulations which are validated against experimental data, including the mass flow rate and indicated pressure measurements. When operating at 1516 rpm and between pressures of 5.4 bar at the inlet and 3.2 bar at the outlet, the supercharged expander provided a power output of 325 W. The specific power output was equal to 3.25 kW/(kg/s) with a mechanical efficiency of 63.1%. The comparison between internal pressure traces obtained by simulation and experimentally is very good. However, the numerical model is not able to account fully for the overfilling of the machine. A comparison between a standard and a supercharged configuration obtained by CFD simulation shows that the specific indicated power increases from 3.41 kW/(kg/s) to 8.30 kW/(kg/s). This large power difference is the result of preventing overexpansion by supercharging. Hence, despite the greater pumping power required for the increased flow through the secondary inlet, a supercharged expander would be the preferred option for applications where the weight of the components is the key issue, for example, in transport applications.

Acetylene hydrogenation reactions (AHR) are typically carried out in fixed bed reactors (FBRs) with high diameter‐to‐particle diameter (D/d). In this study, first, a real catalyst bed was built using the discrete element method, and the suitability of the bed was assessed using empirical equations. Second, a discrete element method‐computational fluid dynamics (DEM‐CFD) model was developed using CFD in conjunction with the reaction mechanism to simulate the AHR in the FBR and was compared with the experimental results. The results show that the DEM‐CFD can well predict the 3D interactions of velocity, temperature, and species for different D/d. The results can provide favorable theoretical guidance for the optimization of FBR and process intensification.

To improve the operational efficiency of a hammer mill and delve into a high-efficiency, energy-saving grinding mechanism, the crucial parameters influencing the grinding of corn straw were identified as the spindle speed, hammer–sieve gap, and sieve pore diameter. According to the force analysis and kinematics analysis, the key factors affecting corn straw grinding were the spindle speed, the hammer–sieve gap, and the sieve pore diameter. The grinding process of corn straw was studied using computational fluid dynamics (CFDs) and the discrete element method (DEM) gas–solid coupling numerical simulation and experiment. The numerical simulation results showed that with the growth of time, the higher the spindle speed, the faster the bonds broke in each part, and the higher the grinding efficiency. When the energy loss of the hammer component was in the range of 985.6~1312.2 J, and the total collision force of the corn straw was greater than 47,032.5 N, the straw grinding effect was better, and the per kW·h yield was higher. The experimental results showed that the optimum combination of operating parameters was a spindle speed of 2625 r/min, a hammer-screen gap of 14 mm, and a sieve pore diameter of 8 mm. Finally, the CFD–DEM gas–solid coupling numerical simulation validation tests were performed based on the optimal combination of the operating parameters. The results showed that the energy loss of the hammer component was 1189.5 J, and the total collision force of the corn straw was 49,523.5 N, both of which were within the range of better results in terms of numerical simulation. Thus, the CFD–DEM gas–solid coupling numerical simulation could accurately predict the corn straw grinding process. This study provides a theoretical basis for improving a hammer mill’s key components and grinding performance. Meanwhile, the proposed gas–solid two-phase flow method provided theoretical references for other research in agricultural machinery.

The existence of defects in the enclosure structure is the primary cause of water and sand leakage in foundation pits, as well as being a significant source of danger in pit construction, but current research lacks an in-depth investigation of the generation mechanism and gestation process. In this paper, which comprehensively considers the microscopic particles and macroscopic level, the development mechanism of a water and sand leakage disaster in a foundation pit with a water-rich sand layer was studied using the principle of computational fluid dynamics and discrete element method coupled analysis (CFD–DEM); moreover, based on the anisotropy of the particle force and fluid energy analysis, the deformation of the stratum and ground stress field were analyzed. The results show that the stress field will produce a plugging effect at a certain distance from the defect, and the strata exhibit a dominant displacement tendency in the vertical direction, resulting in the emergence of a gradually concave stress relaxation zone and an elliptical contour in the strata displacement map near the defect. The fluid energy describes the displacement of the sand layer very well, and it is separated into the sand layer’s centralized loss region and the major loss area based on the high and low levels of the fluid energy class. The impact of fluid at the defect reaches the maximum kinetic energy, which penetrates the structural weakness and causes the loss of sand particles, and the cross-section of the water influx near the defect gradually expands with the loss of particles, indicating that there is a danger of further expansion of the defect under the impact of water flow. These results have technical implications for the management of water and sand leakage disasters in foundation pit engineering.

CFD-DEM simulation of fluorination reaction in fluidized beds with local grid and time refinement method

A novel particle-resolved direct numerical simulations (PR-DNS) method for non-spherical particles is developed and validated in the open-source MFiX (Multi-phase Flow with Interphase eXchanges) code for simulating the suspension of non-spherical particles and fluidisation. The model is implemented by coupling superquadric Discrete Element Method-Computational Fluid Dynamics (DEM-CFD) with the immersed boundary method. The model was first validated by applying it to analyse fluid dynamic coefficients ( $C_{\!D} , C_{\!L} , C_{\!T}$ ) of superellipsoids and cylinders at different Reynolds numbers, and the PR-DNS results closely matched those of previous methods, demonstrating the reliability of the current PR-DNS approach. Then, the model was applied to the simulation of the fluidisation of spheres and cylinders. The PR-DNS results were compared with both particle-unresolved superquadric DEM-CFD simulation and experimental data. The pressure drop, height distribution and orientation distribution of particles were analysed. The results show that the PR-DNS method provides a reliable method for reproducing fluidisation experimental results of non-spherical particles. In addition, the comparison of the drag correction coefficients predicted by existing models with that obtained from PR-DNS results indicates the need for a new drag model for particle-unresolved simulation of non-spherical particles.