Surface Renewal and Residence Time Distribution of Highly Viscous Liquid Falling Film Flow

Abstract

The flow behaviors of highly viscous fluid falling film outside the vertical tube were investigated by theoretical analysis and numerical simulation. Based on gas-liquid two-phase flow methods, a new insight into flow behaviors, which mainly referred to the film thickness distribution, surface renewal frequency and residence time distribution of the highly viscous fluid falling film outside the vertical tube, were provided. Moreover, the correlation between film thickness and fluid viscosity and flow rate was established through model analysis. The numerical simulation results of film thickness were in good agreement with the experimental and theoretical values. The film surface dilated at the beginning of the falling film, and then gradually reached stable state with the largest thickness value. The distribution curve of falling film velocity from wall surface to free surface was in line with the typical Nusselt semi-parabolic profile. Normally, a large flow rate or a low fluid viscosity corresponds to a high surface renewal frequency and a narrow residence time distribution of falling film flow. The dimensionless residence time distribution of falling film flow showed little difference under different conditions, which indicates that the vertical tube falling film flow has a good application prospect in the production of high viscosity materials with uniform quality.