Imposition of the Pressure-Dependent Wall Slip Condition in Mathematical Modeling of the Continuous Processing of Energetic Materials: Twin Screw Extrusion and Die Flows

摘要

A number of studies have indicated that various types of flow instabilities exhibited by polymeric melts and concentrated suspensions of polymeric suspensions are affected by the total normal stress at the wall (which for concentrated suspensions can be assumed to be equivalent to pressure) and the pressure dependence of the wall slip velocity [Tang and Kalyon (2008 a and b). The development of flow instabilities during the flow of concentrated suspensions of rigid particles incorporated into polymeric binders in simple capillary dies (cylindrical reservoir connected to a converging entry region into a straight circular tube) can involve time-dependent changes in the concentration of particles or changes in the shape of the extrudates emerging from tube flow. Time-dependent changes in the concentration of particles generally occur on the basis of time-periodic oscillations in extrusion pressure, upon the formation and break-up of mats of solids at the capillary entrance and the filtration of the binder phase [Yaras et al. (1994); Rough et al. (2000)].