A Unified Continuum Model for Solid Conveying, Melting, and Melt Flow in Single Screw Extrusion

ABSTRACT Simulation of solid conveying, melting, and melt flow in single‐screw extrusion (SSE) is essential for understanding how polymer properties, processing parameters, and screw geometry influence pressure development and throughput. Conventional numerical approaches typically model different extrusion zones separately, leading to discontinuities in the description of material evolution along the screw. In this work, a unified continuum model is developed to represent all functional regions of SSE within a single computational framework. The model combines continuum descriptions of granular flow with enthalpy‐based phase‐change formulations. Two field variables, melt fraction and solid‐bed porosity, are introduced to characterize the evolving material state, enabling a continuous transition from loosely packed pellets to fully molten polymer without explicit zone switching. Granular resistance, wall interactions, and mixture‐averaged material properties are incorporated to allow the conservation equations of mass, momentum, and energy to be solved consistently using a finite‐element method. Model predictions are evaluated against published measurements of solids‐conveying throughput and full‐process pressure and throughput, as well as extrusion experiments using Poly‐Ether‐Ether‐Ketone (PEEK) pellets with different shapes. The results demonstrate that the model provides physically reasonable predictions of pressure evolution and throughput under different processing conditions.