Pickup velocity from particle deposits

In order to optimize the design process of pneumatic or hydraulic conveying systems, all possible modes, cases, patterns etc. of the two-phase flow (fluid-solids) must be known and understood. One of the most significant parameters for designing conveying systems is the threshold velocity for picking up the initially at rest deposited particles. Numerous studies focus on the pickup velocity from a horizontal layer of particles. However, the pickup mechanism from hill-shaped deposits has gained much less attention. The main aim of this work is to investigate the air flow over the deposits of particles (including both horizontal layers and hill-shaped particles) and to determine the minimum air velocity for picking up the particles from the deposits. Based on our experimental results and an empirical analysis of seven different materials, covering a wide range of properties, we found that the pickup velocity strongly depends on the deposit height and shape. It was also found that there is a relationship between the pickup velocities from particle deposits and from a layer of particles. This relationship takes into account the ratio between the wind tunnel and the deposit height and the particulate solids angle of repose which defines the deposit shape.