(124a) Granular Materials and Flows: A Test Bed for Framing and Analysis

Many significant problems in chemical engineering have resisted couching in elegant formalisms, the flow of granular materials being a particularly important example.  There are valuable lessons that come sharply into focus by examining the nature of the difficulties. The objective here is to bring to the forefront questions of framing and analysis: decisions regarding the level of description and caveats constraining the range of solutions. We will present several examples from our own research and that of others to illustrate these two interrelated issues. The first issue is the challenge that lies in picking the appropriate level of description to address a specific question; the choice often being one from among a huge hierarchy of length scales and a range of approaches: continuum, discrete, purely geometrical, with much in between. The second issue, a characteristic of many if not most problems in granular matter, is that solving a problem comes with conditions, often associated with various time and length scales. When one digs deeper one finds more questions.  But simple pictures often yield considerable insight.