(146g) Effects of Wall Boundary Conditions on 3D Simulation of Pseudo Two Dimensional Fluidized Beds Using Dense Discrete Phase Model (DDPM)

Authors: 
Hashemisohi, A., North Carolina A&T State University
Shahbazi, A., North Carolina Agricultural and Technical State University
Wang, L., North Carolina Agricultural and Technical State University
Dense Discrete Phase Model (DDPM) is a new computational fluid dynamic (CFD) approach to simulate industrial scale fluidized bed reactors in a reasonable computational time. It is a hybrid Lagrangian-Eulerian approach tracking the particles in a Lagrangian framework according to Newton’s laws of motion while interactions between particles are estimated by kinetic theory of granular flows (KTGF). However, there are still few studies on the DDPM model and there is a need to study the effect of wall boundary conditions on the CFD simulation of bubbling fluidized beds and identify the controlling factors on simulation of wall effects.

In this work, a pseudo two dimensional fluidized bed (0.3 m × 0.7 m × 0.015 m) was simulated using DDPM and compared with experiments. A three-dimensional computational column was generated to study the movement of particles in third dimension and their collisions with back and front. A mesh dependency study was conducted, and minimum number of cells in depth direction was determined to observe the back and front wall frictions. Specularity coefficient which determines the elasticity of particle wall interactions was changed between 0.0001 to 0.5. Optimum coefficient was calculated in a way that velocity of particles and their circulation patterns had the best consistency with experiments. Moreover, effect of wall friction on size of bubbles, bubble rising velocity, pressure drop was observed. The results showed increase in size of bubbles and void fraction of the system by decreasing the wall friction. Besides, as particles rebounds off the wall in Lagrangian frame, the change in particles momentum can be defined by the normal and tangential coefficient of restitutions. The results showed that restitution coefficient didn’t have that much effect on velocity of particles, and dynamic of bubbles. It was observed that Specularity coefficient is different at higher velocities and it should be calculated for different superficial velocities.