Study on Configuration Design and Numerical Simulation of Twin-Screw Extruder Cooling Die Based on Pea Protein Isolate Flow Properties

This study developed an optimized cooling die configuration to improve the fibrous structure and texture of protein extrudates. Six designs, combining three cross-sectional shapes and two flow channel layouts, were evaluated through numerical simulations based on the physical properties of pea protein isolate (PPI) and extrusion parameters. The results show that PPI exhibits pronounced shear-thinning behavior, with viscosity decreasing by more than 85% as the temperature increases from 35 °C to 135 °C. Among all designs, the rectangular outlet with a serpentine cooling channel performed best, showing a center-to-wall temperature difference of 12.4 °C compared with 7.8 °C for the circular die, a 35% higher heat transfer coefficient, a wall-to-center viscosity ratio of 7.4 compared with 4.9 for the square die and 3.7 for the circular die, and a maximum wall shear rate of 3.42 s−1 compared with 2.15 s−1 for the circular die. The rectangular outlet increases the center-to-wall temperature gradient, while the serpentine channel extends the flow path to raise shear and velocity gradients, together promoting fiber alignment and improving the structure of plant-based meat. These findings provide a theoretical foundation for cooling die optimization and offer a practical approach to control fiber formation in plant-based meat.