Numarical Simulation And Experement Inspection Of Gas-Solid Two Pahse Flow In Maganetically Fluidized Beds

The magnetically fluidized bed (MFB) combines fluidized technology and electromagnetic technology, and it has many advantages, such as higher fluidization quality, better stability and lower bed-pressure drop etc.. Therefore it is a new fluidized technology and widely applied to many industrial fields, for examples, energy, environment protection and foods industry etc..In this dissertation, the hydrodynamic characteristics of the ferromagnetic particles in the magnetically fluidized bed are explained from three aspects: fundamental theory, numerical simulation and experimental inspection. Furthermore, in the experiment, the performance of the magnetically fluidized bed is developed by improving some parts of its devices. The mainly contents of this dissertation are as follows: The theoretical study: Based on analyzing the gas-solid two-phase flow in the magnetically fluidized bed, the mechanism of eliminating bubbles in the bed by magnetic force is interpreted, and both the operational scope and hydrodynamic characteristics of the magnetically fluidized bed with external magnetic field are also analyzed.The numerical simulation study: First, using the software of Gambit to build a 2D fluidized-bed model according to the experimental facility, meshing the 2D model, and specifying its boundary layers. After finishing the work above, the model is imported into Fluent, specifying the boundary condition and parameters' attributions. In this way, the model is initialized and the iterations are also started. Compared the computational results with the experimental results, it shows that the numerically computational results is well coincided with the actually operational conditions of the magnetically fluidized bed. The experimental study: Some parts of the magnetically fluidized bed are improved as follows: 1) The distance between the two Helmholtz coils is elongated with 1.5 times of the radius of each coil to expand the range of uniformity of the magnetic field, 2) The air distributor is designed with caps distributed equilateral-triangle type, which can lead to well fluidized quality, and it also can get more uniform airflow, without causing to be clogged. During the experiment, the characteristics of the gas-solid two-phase flow in the bed are observed and analyzed, using U-Δp curves. A sensor is taken to record the pressure drop of the bed, when increasing (decreasing) the superficial gas velocity. And the initial fluidized velocity and the minimum bubbling velocity are determined for various values of magnetic field intensity. With all these data, the stable zone in the magnetically fluidized bed is got for different intensity of magnetic field, and it shows that the numerically computational results can predict the gas-solid flow in the bed correctly.