DEM study of the flow of cohesive particles in a screw feeder

Screw feeders are widely used in various industries to transfer granular materials at relatively precise rates. The performance can be affected by many factors such as the shape and size of particles, and the design of a screw and associated charging container. Some of these factors are difficult to investigate experimentally, including, for example, the cohesion between particles. In this work, a numerical model is developed by means of the discrete element method to study the flow of cohesive particles in screw feeders. In the model, the magnitude of the cohesive force is assumed, but it can be related to the van der Waals attraction for fine particles or the capillary force for wet particles. Based on the simulated results, a correlation for the prediction of solid flowrate is formulated as a function of the magnitude of cohesive force and the rotational speed of a screw. The mechanisms are then depicted in terms of contact forces and their spatial and temporal distributions. Three flow regimes, namely, continuous, intermittent and stable arch, are identified based on the standard deviation of solid flowrate in a screw feeder. Possible methods to reduce the effect of cohesive force on solid flow are discussed, in the study of the effects of the screw length in the associated charging container as well as the container design. The findings should be useful for the design and operation of screw feeders.