Numerical Study of Solid-Liquid Two-Phase Flow in Stirred Tanks with Rushton Impeller (Ⅰ) Formulation and Simulation of Flow Field

Three-dimensional solid-liquid flow is mathematically formulated by means of the "two-fluid" approach and the two-phase k-ε-Ap turbulence model. The turbulent fluctuation correlations appearing in the Reynolds time averaged governing equations are fully incorporated. The solid-liquid flow field and solid concentration distribution in baffled stirred tanks with a standard Rushton impeller are numerically simulated using an improved "inner-outer" iterative procedure. The flow pattern is identified via the velocity vector plots and a recirculation loop with higher solid concentration is observed in the central vicinity beneath the impeller. Comparison of     

Numerical Study of Solid-Liquid Two-Phase Flow in StirredTanks with Rushton Impeller(Ⅱ) Prediction of Critical Impeller Speed

The critical impeller speed, NJS, for complete suspension of solid particles in the agitated solid-liquid two-phase system in baffled stirred tanks with a standard Rushton impeller is predicted using the computational procedure proposed in Part I. Three different numerical criteria are tested for determining the critical solid suspension. The predicted NJS is compared with those obtained from several empirical correlations. It is suggested the most reasonable criterion for determining the complete suspension of solid particles is the positive sign of simulated axial velocity of solid phase at the location where the solid particles are most difficult to be suspended.     

New Method of Rigorous Modeling and CFD Simulation for Methanol—Steam Reforming in Packed-Bed Reactors

A comprehensive dynamic mathematical model was developed to analyze methanol?steam reforming in catalytic packed-bed reactor. The contributions of all molecular and convective terms of momentum, heat, and mass transfer were taken into consideration, with the inclusion of effectiveness factor. Effects of two predominant parameters: particle size and the wall heat flux on the reactor performance for the methanol?steam reforming were examined. It was revealed that by increasing the average particle size from 700 to 3200 µm, which corresponded to porosity values of 0.4 and 0.6, the effectiveness factor decreased by nearly 80% and subsequently the overall methanol conversion decreased by around 74%. Besides, through a set of organized simulation runs, it was discovered that with increasing the dimensionless wall heat flux from 0 to 0.2 Wm^?1 K^?1, the methanol conversion was enhanced by 87%.     

Flow of a Newtonian fluid and a yield stress fluid around a plate inclined at 45° in interaction with a wall

This experimental and numerical study focuses on the determination of drag and lifts forces acting on inclined plate at 45° placed near a wall in a uniform flow of Newtonian and yield stress fluid. The inertia of the fluid is considered negligible. The influences of yield stress, shear thinning, and the distance between the plate and the wall were examined precisely. It is shown that the drag and lift coefficients decrease as the Oldroyd number increases and increase as the gap decreases. The unyielded zones around the plate were also determined. Their surfaces increase with the Oldroyd number. When the yield stress is low, the decrease of the shear thinning index n tends to decrease these unyielded zones. For the experimental part, a Carbopol gel was used as a fluid model. Experimental measurements were compared with numerical and published results, particularly in the plasticity context developed for soil mechanics. Differences are discussed in terms of the influence of elasticity and plasticity.