LBM-DEM-FEM coupling model: an efficient FSI method to investigate convective heat transfer through non-spherical particle suspensions with particle rotations*

Motivation: Shear-driven particle rotation influences heat transfer at high Peclet number (Shu et al., 2021). For non-spherical particles, the shear-induced movements are much more complicated including motions like tumbling and kayaking. The calculation of both the fluid-structure interaction and the two-phase heat transfer requires precise and efficient numerical methods. This study presents an approach to simulate particle movement and heat transfer by a combination of the Lattice Boltzmann method (LBM, for mass and heat flow of the fluid), the Discrete Element method (DEM, for movement of the particles), and a Finite-Element approach (FEM, for heat flow inside the particle).

Method: The open-source coupled LBM and DEM code is provided by Seil (Seil and Pirker 2017), where the force/torque coupling between fluid and particle follows the algorithm by Noble (Noble and Torczynski 1998). The Lattice Boltzmann Method computes the advective-diffusive behavior of incompressible fluid and imposes the forces acting on the particle to the Discrete Element Method, which in turn computes the particle movements. The velocities of the particle are given back to the LBM. For calculating the heat flow inside the particle, a coupling of a FEM code is added to the LBM-DEM approach by mapping the heat fluxes at the boundary of the particle from the LBM to the FEM. Back-coupling is achieved by transferring the temperature back to the LBM (Suzuki et al. 2018).

Results: Model validation is performed by computing the rotation speed and the effective thermal conductivity of a spherical particle. Results are compared with simulations utilizing the commercial software COMSOL^®, showing good agreement. For non-spherical particle, the shear-driven rotation speed is compared to an approximated Jeffery analytical solution, showing again good agreement.