Numerical Simulation Strategy and Applications for Falling Film Flow with Variable Viscosity Fluids

The flow behaviors for falling film with wide-range variable viscosity were demonstrated by a neosimulation strategy, which incorporated the age transport equation based on mean age theory and a designable age-viscosity formula into Navier–Stokes equations. Surprisingly, a turning region was revealed, in which the thickness variation for variable viscosity falling film with the flow rate and initial viscosity was reversed. The larger the flow rate or the higher the initial viscosity, the longer the length of the turning region, and further, it was from the inlet along the flow direction. A flow cross-sectional viscosity was proposed to explain this anomaly. Then, a simulation scheme for calculating the initial viscosity based on outlet viscosity and an empirical equation for designing the length of the falling film pipe could be achieved according to flow cross-sectional viscosity analysis. It provided a practical reference for falling film reactor design, scale-up, and process optimization.