Numerical simulation of double-layer flow from tube-in-orifice spinnerets

Numerical simulations of double-layer now from tube-in-orifice spinnerets h ave been carried out using a differential constitutive equation. The stream line-upwinding finite element method with 4x4 sub-elements on stress compon ents and overrelaxation method for equation of motion were used. In additio n, the extrudate swell and interface shape have been experimentally observe d for PVP(polyvinylpyrrolidone) aq./water system to check the validity of n umerical results and to relate the flow geometry to the extrudate swell and interface shape. It was found through both numerical predictions and exper iments that extrudate swell shape is strongly dependent on the location of the center tube edge in a tube-in-orifice spinneret. In particular, the min imum of the outer diameter swell was found when the center-tube edge was fl ush with the outer-orifice edge. These results give useful information for choosing the optimal design of a tube-in-orifice spinneret.