Euler-Euler Method Simulating Pulsed Fluidized Bed Behaviors

Fluidized-bed technology has been widely used in energy, chemical engineering, and many other industrial fields. The experimental findings on multiphase flow, heat and mass transfer in fluidized bed are not satisfactory enough to scale up fluidized bed and predict reliable practical results for industrial fluidized bed applications. Numerical modeling and simulation by CFD supplies a potential tool to understand the necessary data for operations and make feasible predictions to the experimental results, and hence it is a very important technique to the practical applications of fluidized bed.Pulsed fluidized bed (PFB) is a variant of fluidized bed, where an additional gas flow is introduced to fluidize the solid materials. It has been reported that PFB can improve the properties of flow, heat and mass transfer in fluidized bed. However, the complex bed behavior is more difficult to study. In this thesis Euler - Euler method were used to numerically simulate the two-phase flows in PFB with drag model, turbulence model and so on, which have been proven reliable. And user-defined functions (UDFs) were programmed to define the inlet pulsed air flow rate, including the pulsating air flow modes, frequency, amplitude, etc. According to the requirements of convergence relaxation factors, time step, discretization and solution methods were suitably chosen.The parameters of fluidized-bed pressure drop waves, gas-solid phase distribution, and bubbles movement were recorded after the numerical results become stable. The relationship between pressure drop fluctuations and pulse frequency and wavetype was obtained, and the effect of pulsating gas flow on the bubbles behaviors, such as generation, growing up, and breaking up, was analyzed. The relationship between the bubble behaviors and the bed high was analyzed too. Bed expansion and fluctuation ratio were studied based on the relationship between bubble behavior and bed height. At last, the general effects of pulsating gas flow on the fluidized bed operations were obtained.Numerical results show that the pulsating gas flow added can initialize bed fluidization at low gas velocity and with the pulsating flow under resonance the fluidized-bed quality can be improved and the turbulence of fluidization is enhanced. The bubbles definition is reasonable and there exists emulsion phase inside the bubble. Bubbles internal pressure changes are mainly influenced by bed height, bubble growing-up rate, and interphase exchanges of particles. According to the velocity vector contour it can clearly see particle phase circulation inside the fluidized-bed due to the bubble behavior, as is valuable to further understand the effect of pulsating gas flow on bed fluidization.