Abstract:
In the design of coat hanger extrusion dies, the main objective is to provide a uniform flow
rate at the die exit. Previously, a multi-rheology isothermal method model for coat hanger extrusion
dies was developed to reach this objective. Polymer melts in extrusion dies commonly experience
high shear rates. Viscous dissipation rooted by high shear rate may lead to significant temperature
differences across the die. Due to temperature-dependency of viscosity, temperature differences
may lead to nonuniform flow rates, which may significantly affect the flow rate at the die exit. As a
result, a new design method is proposed to take into account the effects of temperature and viscous
dissipation in the design of coat hanger dies. Although more non-Newtonian fluid rheology models
can be adapted in the proposed study, as demonstration, temperature-dependent power-law and
Carreau–Yasuda models are adapted in this study. Performances are compared with our isothermal
method published earlier. In addition, the novel nonisothermal method is comprehensively examined
where the effect of viscous dissipation is studied through Brinkman number of extrusion die. It is
demonstrated that, for a low Brinkman number, both isothermal and nonisothermal design give
similar flow uniformity level. However, for higher Brinkman numbers, the proposed nonisothermal
method produces a design with more desirable velocity uniformity level along with a maximum
improvement of 5.24% over the isothermal method. In addition, dependency of flow field on
temperature, due to temperature-dependent viscosity, is studied, and it is demonstrated that fullydeveloped
velocity profile changes as temperature increases along the flow channel. Moreover, the
effect of the temperature sensitivity parameter in temperature-dependent non-Newtonian models is
considered. It is demonstrated that the temperature boundary condition with the Biot number of
1.0 gives adequate results for lower values of the temperature sensitivity parameter.