Polymer Flow in a Melt Pressure Regulator

Abstract

A non-Newtonian, non-isothermal flow analysis has been developed to assist the design of a self-compensating polymer melt regulator, which is a device capable of regulating the melt pressure in polymer processing via an open loop control architecture. The governing mass and momentum equations for the two-dimensional, axisymmetric flow field are solved by a mixed finite element method, in which the velocity components are interpolated by quadratic functions, and the pressure is interpolated by a linear function. The temperature field is solved by the finite difference method. Results of the outlet pressure, valve pin position, bulk temperature rise, and flow rate as functions of the control force for Newtonian isothermal analyses and non-Newtonian non-isothermal analyses are provided. The simulation demonstrates the behavior of candidate regulator designs and provides the performance attributes such as outlet pressure, flow rate, temperature rise, etc., given the decision variables, such as valve parameters, process conditions, and polymer melt rheology. The results indicate that for a regulator design on the order of 20mm diameter, the regulator operates in a mostly closed condition with an aperture opening varying between 0.1 and 1mm. The results suggest that the bulk temperature increases with control force and flow rate and is largely attributable to the increases in viscous heating of the melt through the flow channels, rather than the pinch off between the valve pin and the valve body.