Acetylene Hydrogenation Processes Studied Using CFD in a Packed Bed Reactor

Computational fluid dynamics (CFD) combined with the discrete element method (DEM) are powerful tools for analyzing dense gas–solid flows. However, the computational cost of CFD–DEM will be unfeasibly great when simulating large-scale engineering applications with billions of particles. Accordingly, the coarse-grained (CG) CFD–DEM method is applied to solve this problem. This investigated method replaces several smaller particles with larger ones called parcels, aiming to reduce the number of particles and fully consider the collision of particles between composition parcels and the collision of particles within composition parcels. First, high-speed photography verifies the numerical simulation's reliability. Then, the CG CFD–DEM was used to analyze the transient spatial distribution, transient average velocity, pressure drop, bed height, and the mixing state of particles in a dense gas–solid fluidized bed. The CG CFD–DEM was also compared with the CFD–DEM results, which showed a good agreement with the calculation results and proved the accuracy and applicability of the method. Finally, the computation time of the CG CFD–DEM was evaluated, showing a significant decrease in computation time with an increasing coarse ratio (k). This investigation can provide theoretical reference for the numerical simulation of the CG CFD–DEM method in dense gas–solid flow.

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.

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

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

The combined discrete element method/computational fluid dynamics (DEM/CFD) approach allows for the description of reacting granular assemblies passed by a gas flow. Especially for thermally thick particles, the spatial resolution of the solid object volumes, their surfaces, and of the interstitial flow domain controls the quality of results while at the same time driving computational costs. To evaluate the differences between resolved and unresolved DEM/CFD approaches, pyrolysis of a bulk of spherical wood particles enclosed by a cylindrical heating surface and passed by hot nitrogen is numerically examined. The unresolved simulation is based on the averaged volume method (AVM). For the resolved simulation, the so‐called blocked‐off (BO) method is applied. The results show that the total mass conversion rate of solid particles into gaseous volatiles is faster when employing the resolved BO approach. The better spatial resolution of local flow field and particle surface representation leads to a more detailed prediction of convective and radiative heat transfer to the particles, but is associated with the penalty of a six‐fold computing time.

As subway train‐induced low‐frequency vibrations continue to rise, there is an increasing need for more effective vibration control strategies. Although current low‐frequency vibration reduction methods offer some solutions, further progress is necessary. This paper introduces a novel tuned liquid particle damper‐dynamic vibration absorber (TLPD‐DVA), which merges the principles of tuned liquid dampers (TLDs) and particle dampers (PDs). By capitalizing on the low‐frequency damping capabilities of TLDs, this approach incorporates particles suspended within the liquid to create a hybrid damping device capable of effectively attenuating vibrations across a wide low‐frequency range (10 to 80 Hz). A discrete element method‐computational fluid dynamics (DEM‐CFD) model for multiphase flow is employed to explore the damping mechanism, optimize system parameters, and develop a frequency‐dependent nonlinear damping device. The TLPD‐DVA is then applied to floating slab track systems to control low‐frequency vibrations, and a dynamic interaction model involving the coupled vehicle‐TLPD‐DVA‐floating slab track‐tunnel system is established to assess the system’s response. Harmonic response analysis of a floating slab track fitted with TLPD‐DVAs, along with dynamic mass and mass ratio indices, clarifies the vibration reduction mechanism. Additionally, field tests demonstrate that the TLPD‐DVA reduces vertical acceleration on the floating slab by up to 8 dB and on the tunnel wall by up to 10 dB within the low‐frequency range, surpassing the performance of tuned DVAs. The proposed TLPD‐DVA offers significant potential for vibration control in various civil engineering applications, including transportation infrastructure, building foundations, and vibration‐sensitive facilities.

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.

Coupled discrete element method‐computational fluid dynamics (DEM‐CFD) simulations have been performed to study the fluid and particle dynamics in a fluidized‐bed granulator on the scale of individual particles. Simulation of the gas and particle dynamics is combined with heat and mass transfer mechanisms, as the moisture distribution is a key parameter for the functionality of a fluidized‐bed spray granulator. The model allows monitoring the moisture content and temperature of each individual particle as well as the temperature and humidity of the surrounding gas phase. A novel modeling approach is presented to describe the process dynamics of a fluidized bed in full detail for a reference time interval using coupled DEM‐CFD simulations. The motion profile of gas and particles is extrapolated to larger time scales and used for the calculation of heat and mass transfer. Through this multiscale approach, a step forward is taken towards a physically based description of the microprocesses in granulation.

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.

In inland waterways, waves generated by passing boats cause the movement of riprap used for bank protection and stabilization. Previous studies have mainly concerned the natural channel erosion problem caused by wind-generated waves and neglected the research and findings on shipping behavior. This work presents a coupling of the computational fluid dynamics model and the discrete element method. The aim is to first study the interactions between ship waves in the confined channel and the movements of the riprap of the banks and shorelines and second to analyze the stability of these armourstones under the actions of various ship velocities and draught depths. These varying conditions exert influence on the ship-induced waves, the crucial point being the drawdown amplitude, and consequently create more intense flow behavior in the near-shore region, which results in instability and destruction of the overall structure of the armor protection layer. The higher ship velocity and the larger draught depth lead to the aggravation of instability processes of the blocs composing the protective layer. There is a critical phenomenon in the influence mechanism of vessel velocity, whereas the variation process induced by draught depth is relatively linear. In addition, the stability of the blocs also depends on their shapes, sizes, and the initial positions within the protective layer. This study could contribute to the high-quality development of inland navigation.

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.

A novel pneumatic recovery method was proposed to curb the problem of high losses caused by side-cutting in a rapeseed combine harvester header. The influence of recovery method and material status changes on the recovery effect was studied via the CFD-DEM (computational fluid dynamic- discrete element method) coupling simulation. The effect of airflow action on the recovery effect was compared and analyzed, and the composite pneumatic recovery method was determined. In addition, the influence of material status changes and material feeding rate on the recovery effect was explored, and the critical condition of material blockage in the recovery device was configured. As such, the relationship model between air velocity and recovery rate was constructed and the air distribution ratio of the flow field in the device under this condition was optimized, had verified the rationality of this pneumatic recovery method was verified by a series of field tests. The average rapeseed recovery rate of 92.95% was achieved with the application of the recovery device, and the total loss rate of the header reduced by 52.26%, which is of great significance in reducing the total loss rate of the combine harvesters and improving the operation performance of machinery. The research results can provide a reference for the design of the header structure of a rape combine harvester. Keywords: rapeseed, combine harvester, side-cutting loss, coupled simulation, pneumatic recovery DOI: 10.25165/j.ijabe.20221502.6267 Citation: Jiang T, Zhang M, Guan Z H, Mu S L, Wu C Y, Wang G, et al. Simulation and analysis of the pneumatic recovery for side-cutting loss of combine harvesters with CFD-DEM coupling approach. Int J Agric & Biol Eng, 2022; 15(2): 117–126.

This paper discusses the thermal and exergy efficiency analysis of the hydrothermal liquefaction (HTL) process, which converts sewage sludge into biocrude oil in a continuous plug–flow reactor using a linear Fresnel solar collector. The investigation focuses on the influence of key operational parameters, including slurry flow rate, temperature, pressure, residence time, and the external heat transfer coefficient, on the overall efficiency of biocrude oil production. A detailed thermodynamic evaluation was conducted using process simulation principles and a kinetic model to assess mass and energy balances within the HTL reaction, considering heat and mass momentum exchange in a multiphase system using UDF. The reactor’s receiver, a copper absorber tube, has a total length of 20 m and is designed in a coiled configuration from the base to enhance heat absorption efficiency. To optimize the thermal performance of biomass conversion in the HTL process, a Computational Fluid Dynamics–Discrete Element Method (CFD-DEM) coupling numerical method approach was employed to investigate improved thermal performance by obtaining a heat source solely through solar energy. This numerical modeling approach allows for an in-depth assessment of heat transfer mechanisms and fluid-particle interactions, ensuring efficient energy utilization and sustainable process development. The findings contribute to advancing solar-driven HTL technologies by maximizing thermal efficiency and minimizing external energy requirements.

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.

Boulders in riverbeds significantly influence sediment transport and deposition by altering local flow patterns. This study employs coupled Computational Fluid Dynamics–Discrete Element Method (CFD–DEM) simulations to examine how boulder concentration affects sediment dynamics. Three boulder spacing scenarios, representing isolated, wake-interference, and skimming flow regimes, are evaluated for their impacts on flow structure, bed shear stress distribution, and sediment transport and deposition. The fluid phase is modelled using a large eddy simulation in a finite volume framework, while individual sediment grains are tracked with the discrete element method. The results reveal that increasing boulder concentration transforms the flow regime from isolated wakes behind individual boulders to a more coherent recirculation zone among neighboring boulders. This transition substantially reduces near-bed shear stresses between boulders and leads to a decline in total sediment transport rates. At high boulder concentration, sediment particles preferentially accumulate in sheltered inter-boulder corridors, forming stable depositional belts. In contrast, widely spaced boulders lead to isolated, localized deposition around individual boulders. To our knowledge, this is the first attempt to apply a coupled finite volume–DEM approach to simulate boulder–sediment interactions in open-channel flow, enabling analysis of sediment transport and deposition under varying boulder concentrations.