Quantification of Mechanisms Governing the Angle of Repose, Angle of Tilting, and Hausner Ratio to Estimate the Flowability of Particulate Materials

The angle of repose, angle of tilting, and Hausner ratio are frequently used to estimate the flowabilities of particulate materials. In this study, these parameters were measured for 65 samples. A visualization study showed that there are three mechanisms affecting the angle of repose. Only one is directly related to the flowability. Crucially, to eliminate the effect of wall friction, the measurement of the angle of repose should be conducted on a high-friction surface (such as one covered in glue) or within a ring. Further, although all three parameters can be described as a function of the Archimedes number, the performance of each material was different; thus, the results cannot be generalized. Only the Hausner ratio could be defined reasonably by a single function. A new flowability classification was developed for the three parameters, and the best metric to define flowability was found to be the Archimedes number.