Quantitative Characterization of Powder Flow Under Dynamic Conditions in a Rotating Drum

Control of the flow properties of powders during one or more unit operations of a manufacturing process is an essential part of ensuring that the process is well-controlled.   It is commonplace to incorporate flow-modifying agents to match the flow properties of the powder to those required by the particular unit operation equipment.  Clearly, identifying the most appropriate modifier and the amount required is an untenable option at full production scale. Many physical properties assays exist that allow characterization of powder flow using much smaller amounts of material and in a non-production environment.  However, most of these tests are conducted on powder samples that are static with respect to flow.  Few assays exist that assess the powder under dynamic conditions.  In addition, the equipment used to perform such assays is often expensive and/or has limited flexibility due to design constraints imposed by the vendor.  This work describes an instrument that addresses these issues and presents some practical examples of how it is a valuable complement to traditional methodology.  The instrument's hardware bears a resemblance to a discontinued commercial instrument (TSI Aero‑Flow ?) and the currently available Revolution (Mercury Scientific).  Each instrument employs a rotating drum containing the powder under test and uses optoelectronics to record changes in the location of the powder due to events such as avalanching.  The current instrument differs significantly in regard to the data acquisition and processing algorithms employed.  In particular, inter-frame analysis of the video captured via a camera directed at the drum is used to provide valuable information regarding the movement of powder from one location within the drum to another.  Calculation of traditional two-dimensional image moments allows the inter-frame changes to be represented with a few numerical derived responses.  From these it is straightforward to calculate estimates of such properties as potential and kinetic energies, avalanche time, avalanche mass, avalanche trajectory, relative cohesivity and powder-wall friction.  In addition to the novel processing algorithms, the instrument allows for a persistent record of the video information and subsequent re-analysis with alternative algorithms.  This also enables the operator to compare the derived responses from the analysis with the macroscopic powder flow as seen by a human observer.  It will be shown that two specific calculated responses can adequately describe the macroscopic flow behavior and that they afford simple interpretation in terms of the physical behavior as observed by the operator.  Finally, the instrument is constructed from inexpensive, readily available consumer grade hardware and software, utilizes inexpensive disposable drums and requires typically 1 to 5 grams of powder per measurement.