Comparison of Spherical and Non-Spherical Objects in Cyclonic and Uniaxial Flow Regimes

摘要

This paper uses the Muschelknautz method to model the cyclone separation of chestnut shell and kernel fragments simulated as a square plate and sphere respectively. Because of the opposing geometry of the kernel and shell particles, a new framework is derived using CFD simulations to predict the drag coefficient of the shell particle as a function of orientation and Reynolds number. The drag coefficient of the shell is approximately proportional to the sine of the orientation angle, squared. Despite this, particle orientation remains relatively constant for all practical geometric and velocity parameters within a cyclone, as implied by the assumptions used in this paper. The results from the separation model show that the tangential velocity is almost 86 times greater than the radial velocity of the particle beneath the vortex finder. Consequently, the full frontal area of the particle is not exposed to the radial flow and the particles are not separated effectively by drag force. An experimental separation efficiency of 28.5% compared to an efficiency of 0% predicted by classical cyclone theory, indicates that the shell particles could be re-entrained at the base of the cyclone. This suggests that cyclones do not utilise the differences in drag between particles. The simulation of chestnut kernel and shell particles in a uniaxial flow field (such as occurs in pneumatic separation) shows that it is theoretically possible to achieve a significantly larger separation efficiency when compared to cyclones.