Extension of a coarse grained particle method to simulate heat transfer in fluidized beds

Abstract

The heat transfer in a gas-solids fluidized bed is simulated with computational fluid dynamic-discrete element method (CFD-DEM) and coarse grained particle method (CGPM). In CGPM fewer numerical particles and their collisions are tracked by lumping several real particles into a computational parcel. The assumption is that the real particles inside a coarse grained particle (CGP) are made from same species and share identical physical properties including density, diameter and temperature. The parcel-fluid convection term in CGPM is calculated using the same method as in DEM. For all other heat transfer mechanisms, we derive in this study mathematical expressions that relate the new heat transfer terms for CGPM to those traditionally derived in DEM. This newly derived CGPM model is verified and validated by comparing the results with CFD-DEM simulation results and experiment data. The numerical results compare well with experimental data for both hydrodynamics and temperature profiles. The proposed CGPM model can be used for fast and accurate simulations of heat transfer in large scale gas-solids fluidized beds. 1.Computer simulation is another powerful tool to study heat transfer, such as the computational fluid dynamic coupled with discrete element method (CFD-DEM) [1][2][3][4], which resolves the fluid phase at grid scale and solid phase at particle scale. However, the computation cost of this method is significant due to the large number of particles and small DEM time steps. The coarse grained particle method (CGPM) reduces the computation cost by lumping several real particles into a computation parcel. This method has been used to

Method to estimate uncertainty associated with parcel size in coarse discrete particle simulation

“…13,14 In this method, a number W of real particles are lumped into a computation parcel resulting in fewer parcels to track. 13,14 In this method, a number W of real particles are lumped into a computation parcel resulting in fewer parcels to track.…”

“…The coarse grained CFD-DEM has been implemented and validated in the open-source CFD code MFIX. 13,14 In this method, a number W of real particles are lumped into a computation parcel resulting in fewer parcels to track. The collision forces are calculated using an equivalent diameter of d p W 1/3 while all other forces like drag, gravity, and pressure gradient are calculated at real particle scale.…”

“…Currently, two options extend the capability of this method. This coarse CFD-DEM has been used to simulate chemical reactions, 13 heat transfer, 14 and hydrodynamics 15,16 of fluidized bed and cyclone separators. 9,10 This approach is straightforward but expensive and unavailable to most engineers.…”

“…The second option is to reduce the computational cost by lumping many particles into a computation parcel, 11,12 which results in tracking fewer parcels and their collisions. This coarse CFD-DEM has been used to simulate chemical reactions, 13 heat transfer, 14 and hydrodynamics 15,16 of fluidized bed and cyclone separators. 17 The coarse CFD-DEM reduces the computational cost and induces uncertainties caused by model coarsening.…”

An efficient and reliable predictive method for fluidized bed simulation

“…Although the CFD‐TDHS method is much faster than traditional CFD‐DEM, it is still not fast enough for industrial or pilot scale problems due to the large number of particles in these systems. To further reduce the computation cost in CFD‐DEM, many real particles are lumped into a computation parcel, which has been shown to be efficient for the simulation of CFB riser, pneumatic conveying, cyclone separator, CFB riser, heat transfer, and chemical leaching process of rare earth elements . Also, this method has been reviewed in a recent publication and the influence of drag corrections, grid size, and parcel size are also analyzed .…”