A Multiphase Particle-In-Cell method for simulating particle dispersion in fluidized beds*

Particle dispersion and mixing play a pivotal role in many applications in energy and chemical engineering. One example, are narrow-channel counter-flow fluidized bed heat exchangers, which offer a promising approach to transferring heat out of hot particles, because fluidization provides strong mixing and higher heat transfer coefficients. Such heat exchangers are core component in next-generation Concentrating Solar Power (CSP) plants, which employ high-temperature particle-based Thermal Energy Storage (TES).

 

In this work, we present a Multiphase Particle-In-Cell (MPPIC) method capable of capturing particle dispersion in fluidized beds. Thanks to the use of a continuum particle stress instead of detailed particle pair collisions, this method allows to simulate large number of particles. However, it also presents drawbacks such as overpacking (particles overlapping) and lack of stability. We discuss the issue of overpacking and we show that, while it can be circumvented, this is an intrinsic characteristics of MPPIC methods. We also discuss how to compute the gradient of the particle volume fraction for calculating the particle stress. Finally, we compare our method against the standard MPPIC solver implemented in OpenFOAM and CFD-DEM simulations. We also describe an approach to extract the axial particle dispersion coefficient from experimental measurements of pressure oscillations, and compare it against results from MPPIC simulations.