Particle scale study of heat transfer in packed and fluidized beds of ellipsoidal particles

Abstract

Particle shape can affect the flow and thermal behavior significantly in particle–fluid flow systems. In this work, the combined approach of discrete element method (DEM) and computational fluid dynamics (CFD) is extended to study the heat transfer in packed and fluidized beds of ellipsoids. The aspect ratio of ellipsoids varies from 0.25 to 3.5, representing disk-type and cylinder-type particles, respectively. The conductive heat transfer models for ellipsoids are proposed first, and then the effect of aspect ratio on the bed thermal properties is investigated. It is revealed that aspect ratio affects the effective thermal conductivity of packed beds significantly due to the increased particle–particle contact number and area. The study of bed heating process indicates that compared with spheres, ellipsoids have lower convective heat transfer rate but higher conductive heat transfer rate. In fluidized beds, the convective heat transfer coefficients of prolate particles are larger than those of spheres and oblate particles. The model offers an effective method to examine the effect of particle shape on heat transfer in fluid bed reactors at a particle scale.