Search

Hydrodynamics of helium and fuel particles are simulated in a conceptual helium-cooled spout fluidized bed nuclear reactor. The conceptual reactor consists of an axis-symmetric column with a sharp cone inside which the fuel particles are fluidized by helium. An isothermal gas–solid two-fluid flow model is presented. The kinetic-frictional constitutive model for dense assemblies of solids is incorporated. The kinetic stress is modeled using the kinetic theory of granular flow, while the friction stress is from the normal frictional stress model proposed by (Johnson, P.C., Nott, P., Jackson, R., 1990. Frictional–collisional equations of motion for particulate flows and their application to chutes. Journal of Fluid Mechanics 210, 501–535). Detailed spatial/temporal concentration and velocity profiles have been obtained in a conceptual spout fluidized bed nuclear reactor. The influence of inlet spouting jet velocity and conical angles on flow behavior of fluid and fuel particles is analyzed. The numerical simulations show that the unique mixing ability of the spout fluidized bed nuclear reactor gives rise, as expected, to uniform particle distributions. This uniformity enhances the heat transfer and therefore the power produced by the reactor.

Flow behavior of clusters in circulating fluidized beds was predicted by a proposed two-fluid model using a cluster-based approach (CBA). The model was assumed that the particles move as clusters in the riser. The cluster sizes were estimated from the existing correlations found in the literatures. The distributions of pressure drops, particles concentrations and both gas and solids velocities, and cluster diameters were predicted. A core-annular flow structure in risers was observed from simulations. The numerical results were in agreements with experimental data of [Manyele et al., 2002. Chemical Engineering Journal 88, 151–161] and [Knowlton 1995. Workshop at the Eighth Engineering Foundation Conference on Fluidization].

The fluidization behavior of rice husk–sand mixture in the gas bubbling fluidized bed is experimentally and theoretically studied. The relevancy of the pressure drop profile of rice husk–sand mixture to the definition of its minimum fluidization velocity is discussed, and the minimum fluidization velocity of rice husk–sand binary mixture is determined. The distributions of mass fraction of rice husk particles along the bed height are measured, and the profiles of the mean particle diameter of mixture are determined. A multi-fluid gas–solid flow model is presented where equations are derived from the kinetic theory of granular flow. Separate transport equations are constructed for each of the particle classes, allowing for the interaction between particle classes, as well as the momentum and energy are exchanged between the respective classes and the carrier gas. The distributions of the mass fraction of rice husk particles and the mean particle diameter of binary mixture are predicted. The numerical results are analyzed, and compared with experimental data.

International audience; A numerical study was conducted based on the gas-solid two-fluid model using the body-fitted coordinate system to analyze the behavior of particles and bubbles flow in bubbling fluidized beds without and with immersed tubes. The kinetic theory of granular flow was implemented in the model. The images of simulated instantaneous particle concentration and velocity gave the process of the formation, coalescence and eruption of bubbles. The effects of the tube pitch and superficial gas velocity on the fluidization in a bubbling fluidized bed were investigated. Calculated bubble frequencies without and with immersed tubes were in agreement with previous experimental and simulation findings. The wavelet multi-resolution analysis was used to analyze the simulated data of instantaneous particle concentration. From the random-like particle concentration fluctuations, the fluctuating components due to particle flow and bubble motion can be extracted based on the wavelet multi-resolution analysis over a time-frequency plane.

Based upon fluid dynamics modeling of gas-solids two-phase flows and Euler-Euler two-fluid modeling approach (TFM), incorporated the kinetic model of heterogeneous catalytic reaction, The spouted bed reactor using activated carbon particles to remove SO2 from flue gases was studied. The distribution of SO2 and overall flow patterns including a stable spout region, a fountain region and an annular down comer region within the spouted bed were obtained well. Then, the simulation results of different operating condition were compared. The results show that the rate of desulfurization in the annular region is much higher. And the temperature of reaction, the concentrations of O2 and H2O in flue gases have a prominent influence on efficiency of desulfurization. Such researches verify that proper reducing the reaction temperature and enhancing the concentrations of O2 and vapor in flue gases will improve the efficiency of desulfurization in the spouted bed.