Probabilistic analysis of particle size effects on velocity and impact force in pneumatic conveying

Pneumatic conveying is commonly used for transporting granular materials within manufacturing plants. Conveying fluid velocity within the pipe will display a radial variation being maximum along the centreline and minimum at the walls. Fluid drag force, proportional to the relative velocity between the particle and fluid, will be the primary agent for particle motion in the axial direction. Any random motion that the particle undergoes in the radial direction will mean that the fluid velocity and hence drag force that it is subjected to will also vary erratically with time. Consequently there will be dispersion in particle velocity, and assuming a bend is present in the system, in impact velocity at the wall of the bend. The component of particle velocity normal to the bend wall at impact will be the important component in terms of determining the impact force. The statistics of this normal component of velocity will depend on the statistics of particle axial velocity and the geometry of the bend angle. The maximum impact force at a pipe bend will depend on impact velocity at the bend wall with the precise relationship depending on the structural model that is adopted for the particle. For this work, the particle under investigation is given the properties of Infant Milk Formula and its performance examined in the range from a particle radius of 100 μm up to 200 μm. It is shown that larger particles will experience an impact force characterised by a high mean value while smaller particles will be subject to an impact force with a significantly lower mean value though relative dispersion in impact force is almost independent of size.