Characterization of powder flow: Static and dynamic testing

Many characterization techniques are available to determine the flow properties of powders; however, it is debated which method(s) are the most appropriate. In this study, sample fine powders with a medium particle size between 22 and 31 µm were characterized using a variety of techniques that tested powders under different stress states, ranging from static to dynamic. It was found that characterization techniques that were more dynamic such as fluidized bed expansion were best suited for predicting the fluidization performance while characterization techniques that were more static such as cohesion were better for predicting agglomeration. It was also found that results from static and dynamic characterization do not necessarily agree, where fine powders that showed good fluidization performance also displayed increased agglomeration, and vice versa. This suggests that flow properties are dependent upon the stress state and that no single technique is suitable for the full characterization of a powder. In other words, both static and dynamic characterization techniques must be employed to completely understand the flow properties of a powder and predict how it will behave under different process conditions.