Modelling of Particle-Wall Sustained Contacts in n-Euler Simulation of Dense Fluidised Beds and Comparison with CFD-DEM Predictions

Gas-solid fluidised beds are often modelled using a Euler n-fluid approach that treats the gas and the particles as dynamically coupled interpenetrating continua. In general, the modelling of the solid phase relies on the kinetic theory of granular flow (KTGF), which assumes that particle collisions are instantaneous and binary (Fede et al., 2016). In particular, the wall boundary-condition models developed in the literature, according to the KTGF, do not consider any long-duration contacts between the particles and the wall. However, the sustained contacts of particle assemblies with the wall can play a crucial role for dense-fluidisation regimes (Nigmetova et al., 2022). We have implemented in the multiphase n-Euler code neptune_cfd a wall boundary condition for the particles that aims to address this limitation. The model accounts for both the friction due to short-duration collisions and due to sustained wall-particle contacts. This is achieved through the introduction of a frictional stress at the wall, proportional to an inter-particle frictional pressure, that becomes dominant in dense regimes (α_p>0.5). The boundary condition is therefore uniformly valid from the dilute flows encountered in riser to the dense-fluidisation regime. The relevance of the model is demonstrated a posteriori, for the Euler n-fluid simulation of a pressurised gas-solid cylindrical fluidised bed of olefin particles in the bubbling regime. The numerical analysis leverages reference experimental and numerical data from the literature. The Euler n-fluid time-averaged particle velocities are compared to positron emission particle tracking (PEPT) measurements (Fede et al., 2016). The time-averaged statistics of α_p, of particle and fluid velocities and of the wall friction are compared with high-fidelity CFD–DEM simulation results (Nigmetova et al., 2022).

References:

Fede, P., Simonin, O., Ingram, A., (2016). Chem. Eng. Sci. 142, 215–235.

Nigmetova, A., Masi, E., Simonin, O., Dufresne, Y., Moureau, V. (2022). Int. J. Multiphase Flow 156, 104189.