| Abstract: | Steady three-dimensional laminar flow with and without partial solidification of an initially molten polymer in square ducts, both straight and with a 90-degree curve, was numerically studied with a version of the SIMPLE algorithm. The non-Newtonian characteristics of the fluid polymer were represented by a power-law model. The temperature variation of fluid properties was taken into account. Viscous dissipation, being significant for all flow regimes studied, provided thermal energy input which was balanced by heat transfer outward across duct boundaries. For the non-Newtonian fluid with solidification and variable viscosity, it was found that the effective heat transfer coefficient in the curved section of the square duct is larger than in a straight section; in the curved section, this coefficient is larger at the outside of the bend than at the inside. These findings are in agreement with measurements reported in the literature for similar situations. The combined mechanisms of solidification on the wall and viscous dissipation result in the possibility of two different flow rates for a specified pressure gradient. The flow channel that remains unfrozen in a curved square duct meanders within the confines of the duct much as a river meanders in its valley; the wave length of the meander is sensitive to the fluid flow rate and radius of curvature. |
