Influence of Solid-Phase Wall Boundary Condition on CFD Simulation of Spouted Beds

The Influence of Solid-Phase Wall Boundary Condition in Terms of Specularity Coefficient and Particle-Wall Restitution Coefficient on the Flow Behavior of Spouted Beds Was Investigated using Two-Fluid Model Approach in the Computational Fluid Dynamics Software FLUENT 6.3. Parametric Studies of Specularity Coefficient and Particle-Wall Restitution Coefficient Were Performed to Evaluate their Effects on the Flow Hydrodynamics in Terms of Fountain Height, Spout Diameter, Pressure Drop, Local Voidage and Particles Velocity. the Numerical Predictions Were Compared with Available Experimental Data in the Literatures to Obtain the Suitable Values of Specularity Coefficient and Particle-Wall Restitution Coefficient for Spouted Beds. the Simulated Results Show that the Solid-Phase Wall Boundary Condition Plays an Important Role in CFD Modeling of Spouted Beds. the Specularity Coefficient Has a Pronounced Effect on the Spouting Behavior and a Small Specularity Coefficient (0.05) Can Give Good Predictions, While the Particle-Wall Restitution Coefficient is Not Critical for the Holistic Flow Characteristics. © 2011 Elsevier Ltd

Direct Numerical Simulation and Visualization of Biswirling Jets

Two parallel swirling/rotating jets with a distance between them are termed biswirling jets here, which have important and complicated vortex structures different from the single swirling jet due to the negligible vortex-vortex interactions. The visualization of vortex-vortex interaction between the biswirling jets is accomplished by using direct numerical simulation. The evolution of vortex structures of the biswirling jets is found rather complicated. The turbulent kinetic energy and turbulence dissipation in the central convergence region are augmented locally and rather strongly. The modulation of turbulent kinetic energy by jet-jet interaction upon different scales of vortices is dominated by the swirling levels and the distance between the jets. The turbulent kinetic energy upon intermediate and small scale vortices in bijets with not very high swirling level and at a very close distance is smaller than that in single swirling jets, whereas the opposite is true under a far distance, and so forth

Direct Numerical Simulation of Particle-Laden Swirling Flows on Turbulence Modulation

The modulation of turbulence by the laden particles in swirling flows is studied via direct numerical simulation. The statistical characteristics of turbulence modulation are investigated in detail under the effects of different mass loadings as well as Stokes numbers. It is found that the characteristics of turbulence modulation for different Stokes numbers are very similar to each other when the mass loading is light. As the mass loading increases, small particles seem to modulate turbulence more rapidly than large particles. The number concentration or the number flow rate of particles plays an important role in modulation of turbulence. It induces the preferential attenuation of turbulence for small particles in the near field region. Moreover, the trends of modulation of the axial/azimuthal fluctuations, the turbulent kinetic energy, and the Reynolds stress tenor as well as its invariants are similar in the near field region. However, when the turbulence is decayed sufficiently in the downstream region, the inverse turbulence modulation may occur especially for the regions with local intensive accumulation of small particles

Modification of the Acidic and Textural Properties of HY Zeolite by AHFS Treatment and Its Coke Formation Performance in the Catalytic Cracking Reaction of N-Butene

Coke formation on n-butene cracking catalyst is the main reason for the reducing of its lifetime. To study the effects of acidity and textural properties on the coke formation process, a series of HY zeolite-type catalysts were prepared by ammonium hexafluorosilicate treatment (AHFS). NH3-TPD and Py-IR-TPD were used to systematically study the change law of zeolite acidity. It was found that with the increase of AHFS concentration, the acid density decreased, whereas the ratio of Brønsted acid to Lewis acid first increased and then decreased. Meanwhile, the percentage of Brønsted acid inside the supper cages increased and the strength of Brønsted acid increased with the degree of dealumination. Combined with in situ IR study on coke formation, the relationship between coking and acid site was revealed. It was found that the rate of coke formation on zeolites was affected by acid density, which is the rate of coke formation decreased with the decline of acid density. When the acid density remains at the same level, it was the acid strength that determined the coke formation rate—the stronger the acid strength, the faster the coke formation rate

Modification of the Acidic and Textural Properties of HY Zeolite by AHFS Treatment and Its Coke Formation Performance in the Catalytic Cracking Reaction of N-Butene

Coke formation on n-butene cracking catalyst is the main reason for the reducing of its lifetime. To study the effects of acidity and textural properties on the coke formation process, a series of HY zeolite-type catalysts were prepared by ammonium hexafluorosilicate treatment (AHFS). NH3-TPD and Py-IR-TPD were used to systematically study the change law of zeolite acidity. It was found that with the increase of AHFS concentration, the acid density decreased, whereas the ratio of Brønsted acid to Lewis acid first increased and then decreased. Meanwhile, the percentage of Brønsted acid inside the supper cages increased and the strength of Brønsted acid increased with the degree of dealumination. Combined with in situ IR study on coke formation, the relationship between coking and acid site was revealed. It was found that the rate of coke formation on zeolites was affected by acid density, which is the rate of coke formation decreased with the decline of acid density. When the acid density remains at the same level, it was the acid strength that determined the coke formation rate—the stronger the acid strength, the faster the coke formation rate