Effect of material elasticity and friction on particle dynamics during dilute pneumatic conveying

Dilute phase pneumatic conveying is a widely-used process in the process industries. It is common to convey different products in a single conveying system. However, the pressure drop in the pneumatic conveying line depends heavily on material properties, which also have a direct impact on the conveying capacity. The present work explores the effect of material elasticity and surface friction on pressure drop using blends of hard and soft plastic pellets with different blend ratios in a dilute conveying system. The pellets used have similar particle size, shape and density but different elasticity and surface friction. The conveying friction factors were calculated using the most commonly used correlations and are measured experimentally. The results show a significant lack of fit for the friction factors when conveying materials with a high ratio of soft pellets. In addition, an impact test was performed to isolate the material surface friction effects from elasticity by adding a small amount of water on the surface of soft pellets to reduce particle-wall friction. The impact test results showed that for the dry soft pellets, the angle of rebound is significantly larger than the angle of incidence, which explains their intense bouncing and occasional backward motion during pneumatic conveying. In contrast, for the wet soft pellets and dry hard pellets the angle of rebound is smaller than the angle of incidence, indicating that these pellets bounce less frequently during conveying. This difference demonstrates that the particle-wall friction has a strong effect on particle dynamics during pneumatic conveying.