(645a) 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.