Analysis of extrudate swell from an annular die

An isothermal annular jet swell problem has been analyzed using a control volume based finite difference scheme. This numerical scheme has been previously used for the analysis of the jet swell problem in capillary and slit dies, and is also shown to be applicable to annular geometries as well. In the absence of gravity and surface tension, the thickness swell ratio reaches 15.88%, which is in reasonable agreement with values reported in the literature. A relatively long jet was employed in this study and the effect of gravity on the jet shape appeared to be significant. In accordance with other calculations in the literature, the surface tension was found to have a more pronounced effect on the inner free surface compared with the outer free surface. The effects of the power-law index and die gap size were also investigated, and a suggestion for improvement of the numerical approach is briefly described.