Numerical investigation of the air-particles heat transfer characteristics of moving bed - effect of particle size distribution

Abstract Particle vertical moving beds (PVMB) are widely used in industry, usually accompanied by gas-solid heat exchange or chemical reaction. It is worth noting that the actual industrial particles usually have a wide particle size distribution (PSD), which is an important property that can influence the hydrodynamics and heat conversion in moving bed system. Therefore, understanding the multiphase flow and thermal behavior of PVMB with multi-size particles is essential for process designing and optimizing. Based on the CFD-DEM coupling method, a mathematical model of gas-solid heat transfer for PVMB with different PSDs is established- all with the same mean particle diameter. Furthermore, the effects of 3 influential factors on the exergy transfer in a small PVMB were analyzed. Results show that an increased PSD range leads to an increased specific surface area, but this does not imply a favorable heat transfer between air and particles in PVMB, which is contrary to the findings related to the fixed bed. Increasing particle mass flow rate or particle inlet temperature will cause the cooling air and particle outlet temperature to increase approximately linearly. More interestingly, as inlet air mass flux increases, exergy recovery efficiency decreases, however with the further increase of inlet air mass flux, exergy recovery efficiency reaches a minimum and then gradually increases. Exergy recovery efficiency decreases and tends to be flat with increasing particle mass flow rate. This method is an essential procedure for modeling the heat transfer of discrete particles in industrial-scale equipment.