Effect of local disturbance on the particle–tube collision in bubbling fluidized bed

A numerical investigation on the effect of local disturbance of gas turbulence on the probability distribution function (PDF, for shot) and the rate of particle–tube collision in bubbling fluidized bed is carried out. A two-dimensional (2D) fluidized bed with 6 and 18 immersed tubes (a tube bank) and a three-dimensional (3D) bed with two immersed tubes are simulated, respectively. The local disturbance of gas turbulence is introduced by a blowing gas flow injected from the underneath of the immersed tubes (2D) and from the walls of the bed (3D), respectively. In two-dimensional, the blowing gas flow is injected upstream, downstream or not injected; whereas in the three-dimensional case the gas flow is injected from the side walls of the bed. A DEM-LES coupling simulation method is applied. The results indicate a great increase in particle–tube collision rates and a change in the PDF profiles when the local disturbance is introduced, especially for the case of upstream disturbance. Two main mechanisms are interpreted, i.e. the turbulence augmentation and the formation of weaker velocity regions which both contribute to the changes in characteristics of particle–tube collision but act in independent ways.