Effect of Viscous Dissipation on Polymer Melt Flow in Microscale Channels

ABSTRACT

Intense shear during micro‐injection molding generates viscous dissipation. In this study, a test apparatus was developed to measure the temperature rise induced by viscous dissipation. Using high‐density polyethylene (HDPE), flow experiments were conducted in microcapillary dies with diameters of 350, 500, and 1000 μm. By integrating experimental measurement with numerical simulation, a temperature field reconstruction method was proposed to obtain the actual wall temperature distribution along the flow direction. Based on the Cross‐WLF viscosity model, the evolution of melt viscosity affected by dissipation‐induced temperature rise was systematically analyzed. The results show that melt viscosity decreases along the flow path, featuring a sharp drop near the inlet followed by a gradual decline. Increasing the shear rate intensifies viscous dissipation, leading to a temperature rise and nonlinear viscosity reduction. At an inlet temperature of 240°C and a shear rate of 10,000 s ⁻¹ in the 1000 μm die, the viscosity reduction per unit length reaches 71%. A distinct scale effect is observed: as the die diameter decreases, the influence of viscous dissipation becomes more prominent. At identical conditions (220°C, 10000 s ⁻¹ ), the viscosity reduction per unit length in the 350 μm die is 133% higher than in the 1000 μm die.