R.L.C. Flemmer

On the drag coefficient of a sphere

Abstract A mathematical approximation to experimental data on the drag coefficient of a sphere is presented. The approximation is compared with other approximations and shown to be significantly better both in range and in accuracy. The Newton-Raphson technique is applied to the approximation, allowing the computation of the terminal velocity from a knowledge Of C d Re 2 and of particle diameter from a knowledge of Re/C d .

An experimental study on the effect of particle shape on fluidization behavior

Abstract Few correlations exist to describe the effect of particle shape on the relationship between superficial velocity and void fraction in homogeneous fluid beds. Limestone, quartz, bottom ash and pea gravel particles were fluidized with water and a data bank of void fractions and fluidizing velocities was compiled. Each particle type was image analyzed to yield average shape descriptors, namely aspect ratio, fractal dimension, polygonal harmonic persistences and delta (Pipers) angles. Regression showed that the slope of a log (superficial velocity) versus log (void fraction) plot can be fitted using a function of a shape descriptor, with the persistence of the third harmonic being the descriptor yielding the best fit.

Flow rates of dry powders in inclinded rotating cylinders under open-ended discharge conditions

Abstract A physical model is presented which describes axial flow of dry powders through inclined rotating cylinders under conditions of open-ended discharge. The model has been solved numerically for a wide range of operating conditions. The results are presented as a series of curves expressing local and cumulative fractional filling levels as a function of dimensionless position along the cylinder, mass flow rate, and cylinder inclination. Experimental verification of the model was obtained on a laboratory scale for a limited number of mass flow rates and cylinder inclinations.

The effect of particle shape on fluid-particle interactions

ABSTRACT Few correlations exist to predict the drag on non-spherical particles, although drag on spheres has been well characterized. A problem in developing predictive equations is the lack of adequate shape descriptors, although sphericity is a good descriptor for smooth nonspherical particles, such as geometric objects. Following a review of the topic, an approach to predicting drag on smooth particles is developed by modifying the Turton-Levenspiel equation for drag on a sphere, using sphericity as the shape descriptor. An alternative approach using polygonal harmonics as shape descriptors, proved less accurate.

HYDRAULIC TRANSPORT OF ABRASIVE SOLIDS: THE AIR-LIFT PUMP

ABSTRACT Although the air-lift pump has been superseded by submersible pumps in raising water from wells and mines, it still provides an attractive means of lifting abrasive slurries because, unlike mechanical pumps, it has no moving parts to wear. However, current design of air-lift pumps must rely on empirical equations, or, at best, incremental computer solutions. Design is complicated by the fact that relative velocities of the phases change over the whole pump length. A new design equation is developed to predict the lift of an air-lift pump, given the flowrates of air, liquid and solid in the pump, and the dimensions of the air-lift tube. The new equation is baaed on well-established multiphase flow theory, and offers significant advantages over current design techniques. In combination with an equation for the overall pump efficiency, the new equation provides a method for optimizing the design parameters for the air-lift pump.