Simultaneous hydrodynamic and thermal flow development of a thermodependent viscoplastic fluid

Abstract

Numerical analysis of simultaneously developing forced convection laminar flow and heat transfer of a viscoplastic fluid has been carried out. This fluid is incompressible and of thermodependent rheological properties. It consists on the sloe fruit juice with low pulp and pectin contents, which obeys the rheological law of Bingham and for which we adopt the Papanastasiou model to describe its behaviour. The flow takes place in an isothermal circular pipe. In order to validate the computing code, parametric computations were performed to investigate the effect of Reynolds, Prandtl and Bingham numbers on heat transfer. The effect of wall-to-inlet temperature difference on velocity and temperature profiles, Nusselt number and apparent friction factor was then analysed, by taking into account the temperature dependency of the fluid’s plastic viscosity and yield stress, for both heating and cooling situations. The results show on one hand, that the variability of the plastic viscosity provides more effect on hydrodynamic and thermal characteristics than the variability of the yield stress. On the other hand, the effect of variable plastic viscosity is more pronounced on the friction factor than on the Nusselt numbers