CFD modelling and performance analysis of a twin screw hydrogen extruder

Abstract

An intermeshing counter-rotating twin-screw extruder is reported to be more reliable and stable among various methods of extrusion techniques in pellet production systems for the plasma reactors. In the present study, CFD modelling has been successfully carried out using POLYFLOW module of ANSYS, which employs the Mesh Superposition Technique. The shear rate dependent shear stress of solid hydrogen modelled using Herschel-Bulkley equation has been used in the present analysis. A three-dimensional computation neglecting inertia and gravity effects has been carried out to simulate the flow through the extruder which involves leakage flows through the calendar, tetrahedron, flight and side gaps. The flow characteristics of the die was simulated independently and superimposed with the extruder pumping characteristics to arrive at the operating point. The CFD results have been compared with those obtained from an analytical model adopted from the literature on polymer extrusion research. It has been found that the deviation between them becomes narrow when the mechanical clearances of the extruder are made smaller. A systematic parametric analysis was carried out to arrive at an optimum design to produce a 3 mm diameter filament at about 400 mm3/s with a minimum viscous dissipation rate. The analysis revealed that an increase of pitch length or decrease of mechanical clearance gaps in association with either decrease of the number of ‘C’ chambers or the speed will result in smaller viscous dissipation rate.