| Summary: | 碩士 === 臺灣大學 === 化學工程學研究所 === 98 === Computational fluid dynamics ( CFD ) was used to solve the fluid mechanics problems by using the commercial software FLUENT in this study. The software was used to simulate flow field and calculate the relevant variables related to fluid mechanics such as velocity, pressure, etc. Finally, the simulation results were compared with the experimental data in the literatures to discuss its correctness and feasibility.
The first part of this study was free turbulent jet flow field simulation. The fluid was air, which was at high speed and emerged from a 1 mm diameter circular hole into a semi-infinite stationary air flow. The main flow region was formed near the central axis, and in that region the axial velocity distribution profile changed similarly with increasing the distance from the jet exit. This is called self-similarity of jet flow. The problem was solved analytically in early days; now it also was solved numerically for comparison.
The second part was gas-solid fluidized bed simulation. The two-fluid model ( TFM ) which considered the behavior of both gas phase and solid phase as the fluid was applied to simulate Group A particles flow pattern in the fluidized beds. Due to Geldart Group A particles, the particles which formed clusters when operating in the high gas flow circulating fluidized beds. Due to the effect of the clusters, the classical gas-solid drag force model can not simulate the dilute up and dense bottom axial voidage distribution successfully. With the help of the modified drag force model, the axial voidage distribution profile of FCC particles ( the particle size 58 μm and the density 1780 kg/m3 ) were simulated under fixed solid circulation rate but different superficial gas velocities. The simulation results showed that the particle concentration in the dense region was larger than the expected value, but in accordance with the experimental data in the dilute region.
Leu and Tsai (2009) obtained the minimum bubbling velocity of Geldart group A particles by correlation of pressure fluctuations experimental data. The glass beads ( the particle size 60 μm and the density 2510 kg/m3 ) in bubbling fluidized beds were simulated by using both absolute pressure fluctuations method and differential pressure fluctuations method respectively. The method of determining minimum bubbling velocity in the literatures could be verified by the simulations.
|
|---|
