[paper online] Gas-solid flow and heat transfer in fluidized beds with tubes: Effects of material properties and tube array settings

Gas-solid flow and heat transfer in fluidized beds with tubes: Effects of material properties and tube array settings

http://www.sciencedirect.com/science/article/pii/S0032591015002326

Q.F. Hou, , Z.Y. Zhou, A.B. Yu

doi:10.1016/j.powtec.2015.03.028

Highlights
*Heat transfer and gas-solid flow in fluidized beds with tubes are investigated.
*Different mechanisms are revealed for non-cohesive and cohesive particles.
*The uniformity of particle velocities and temperatures is analysed.
*Complicated variation of heat transfer is demonstrated for different array settings.
*Microscopic local porosity and contact number are linked to macroscopic behaviours.

Abstract
The effects of material properties and tube array settings on gas-solid flow and heat transfer characteristics in fluidized beds with tubes are investigated by the combined approach of computational fluid dynamics and discrete element method, incorporated with heat transfer models. First, the effect of material properties is illustrated by considering cohesive and non-cohesive powders with different particle sizes. The contributions of different heat transfer mechanisms are discussed at two tube temperatures. Significant differences of gas-solid flow between cohesive and non-cohesive powders are observed. The results reveal that conductive heat transfer between a fluidized bed and a tube is dominant for small cohesive particles while convective heat transfer is dominant for large non-cohesive particles. Then, the uniformity of particle velocity and temperature fields is analyzed. It is shown that material properties and gas velocity affect the uniformity of particle velocity and temperature in a complicated manner. Finally, the effect of tube array settings is examined in terms of two geometrical parameters for both in-line and staggered settings. Complicated gas-solid flow and heat transfer characteristics are observed. An effort is made to link macroscopic observations to microscopic information such as local porosity and contact number between fluidized particles and tubes. The findings should be helpful for the optimization of operation and design of fluidized systems with tubes.