Numerical investigation of the gas–solid heat transfer characteristics of packed multi-size particles

Abstract

Real industrial particles generally have a wide size distribution. Therefore, the gas–solid heat transfer characteristics of packed multi-size particles should be studied. A mathematical model of gas–solid heat transfer for packed multi-size particles is established. This model includes gas–solid convection heat transfer and intraparticle and interparticle conduction. The cooling processes of packed binary- and quintuple-size particles ranging from 10 mm to 60 mm under different conditions are investigated. The EDEM software is used to obtain the porosities of different cases. Results show that the presence of small particles in the packed multi-size particles reduces porosity and increases specific surface area, thereby benefiting the gas–particle heat transfer process. The temperature of large particles is always higher than that of small particles during particle cooling. Particle–particle conduction helps in the cooling process of large particles, and the maximum heat flux ratio of interparticle conduction to gas–solid convection for large particles reaches 0.196. The volumetric heat transfer coefficient of the packed multi-size particles varies with time. The initial heat transfer coefficient is the average value weighted by mass fractions, and the limit of the final value is that of the large particle under the actual porosity. The proposed dimensionless volumetric heat transfer coefficient can be a general description of gas–solid heat transfer characteristic of various packed multi-size particles. Its time variation can be well described by an exponential correlation, and the variation rate is related to the variance of particle size in each case.