DEM-CFD Method Research Articles

Modeling and Simulation of Mono-Layer Coating

Coating simulations of nano-suspended particles are implemented using the DEM-CFD method. A new model of capillary interactions, accounting for the microscale interface deformation implicitly but allowing a rather fast calculation time, is implemented. The drying of a nano-suspension liquid layer is modeled and implemented to the DEM code, allowing transient examination of mono-layer aggregation. The effect of particle size on the coating process is investigated. The main contrast in particle size was received in terms of the transition periods to the finite structure. It was found that the non-dimensional liquid height is a correlative parameter between the cases. Aggregation appears to start at approximately the same non-dimensional liquid height. Furthermore, a firm final structure was obtained at a similar liquid level, way before the drying is complete, indicating that the liquid level has a significant control on the assembly until this point.

Numerical investigation of gas-particle flow in the primary air pipe of a low NOx swirl burner – The DEM-CFD method

The gas-particle flow in the primary air pipe (PAP) of a low NOx swirl burner was investigated using the computational fluid dynamics (CFD) coupled with the discrete element method (DEM). The mathematical models were validated using the measured values obtained at the outlet of the primary pipe through a phase Doppler anemometer (PDA) system. Particles of different Stokes numbers in the primary air pipe (PAP) were investigated, and the effects of the structure of the primary air pipe and the particle–particle interaction on particle dispersion were analyzed. The results indicate that particles under the combined effects of the Venturi pipe and the spindle body are concentrated into a narrow band area and that the PAP structure can more efficiently concentrate particles with large Stokes numbers. The formed fuel rich/lean jet persists for a long distance out of the burner, thereby favoring of air-staged combustion and NOx reduction. The particle collision frequency and its fluctuation range increase as the particle Stokes number increases. The collisions among particles result in an increase of the spanwise dispersion of particles. Experimental results indicate that the models that take particle–particle collision into consideration are more able to predict particle concentration.

Using the DEM-CFD method to predict Brownian particle deposition in a constricted tube

Modelling of the agglomeration and deposition on a constricted tube collector of colloidal size particles immersed in a liquid is investigated using the discrete element method (DEM). The ability of this method to represent surface interactions allows the simulation of agglomeration and deposition at the particle scale. The numerical model adopts a mechanistic approach to represent the forces involved in colloidal suspensions by including near-wall drag retardation, surface interaction and Brownian forces. The model is implemented using the commercially available DEM package EDEM 2.3®, so that results can be replicated in a standard and user-friendly framework. The effects of various particle-to-collector size ratios, inlet fluid flow-rates and particle concentrations are examined and it is found that deposition efficiency is strongly dependent on the inter-relation of these parameters. Particle deposition and re-suspension mechanisms have been identified and analyzed thanks to EDEM's post processing capability. One-way coupling with computational fluid dynamics (CFD) is considered and results are compared with a two-way coupling between EDEM 2.3® and FLUENT 12.1®. It is found that two-way coupling requires circa 500% more time than one-way coupling for similar results.

Modelling spray coating using a combined CFD–DEM and spherical harmonic formulation

The ability to coat particles with a uniform film of a desired thickness is a key requirement in many industries such as pharmaceuticals, food processing and chemical manufacture. Controlling the distribution of the coating material during coating operations is essential for ensuring factors such as homogeneity in the coating thickness and prevention of agglomeration, which are common requirements in most types of coating applications. Despite the significant industrial and commercial importance of spray coating, few numerical models have been developed to model this process. Here, we detail the first computational model to incorporate particles, coating spray droplets and gas flow, dynamically interacting over an entire coating system. Particles and gas flow are modelled using a coupled DEM-CFD method, and spray droplets are modelled as individual Stokesian particles within the gas flow field. The coating model uses a newly developed method for mapping the coating coverage over each particle, based on a spherical harmonic formulation. This allows the coating to be evaluated at an intra-particle level on each individual particle. Distribution functions, such as coating quality and volume deposition, can be easily determined for the entire system at the inter-particle level. The method is applied to a test case of an fluidised bed spray coater, and the effects of varying geometry and system operating conditions are evaluated in terms of the coating coverage and quality. The method enables factors affecting coating distribution in such systems to be investigated and understood, and potential design optimisations to be evaluated.