Three-dimensional non-isothermal extrusion flows

Abstract

A three-dimensional (3-D) non-isothermal study of viscous free-surface flows with exponential dependence of viscosity on temperature is presented. The effects of non-isothermal conditions and/or geometry on the extrudate shape are investigated with a fully three-dimensional finite element/Galerkin formulation. Apart from the well known thermally induced extrudate swelling phenomenon, bending and distortion of the extrudate may occur because of temperature differences and/or geometric asymmetries. A temperature difference across the die can be imposed by heating or cooling the die walls, but can also arise because of asymmetric viscous heat generation due to the die geometry. Temperature differences affect velocity profiles because of the temperature dependence of viscosity and lead to extrudate bending, an effect known as "kneeing" in the fiber spinning industry. It is also shown numerically and confirmed experimentally that the die geometry induces extrudate bending even in the case of isothermal Newtonian flows.

Three-dimensional studies on bicomponent extrusion

“…Further numerical implementation details are provided in the previously mentioned references [18,21].…”

“…The tendency of the less viscous fluid to encapsulate the more viscous fluid leads to a curved interface, especially near the die walls. The spine method [17,18,21,25] for the interface parametrization is very well suited for this problem. The interface node x~ is parametrized as (Fig.…”

“…The flow domain is discretized into 27-node brick elements combined in some cases [18,21] with 18-node triangular prism elements. Within each element, velocity and pressure are approximated by:…”

Exposed-core microstructured optical fibers for real-time fluorescence sensing

“…This caused an asymmetry in the viscosity profile and thus bending in the preform during extrusion. In addition, the use of an asymmetric die can cause bending, even in isothermal conditions [19]. Several methods were employed to overcome preform bending.…”

Numerical modeling of multilayer film coextrusion with experimental validation

“…Since DTF's polyester melt viscosities are independent of shear rate but dependent on temperature, this approach is of limited relevance to this work. Karagiannis et al [55] used a finite element code to demonstrate that nonisothermal effects in mono-component extrusion can lead to phenomena such as extrudate swell. When investigating polymer coextrusion, Sunwoo et al [56] and Mallens and Waringa [17] implemented temperature effects into their finite element simulations.…”