Modeling of fluid dynamics in wiped film evaporators during evaporation

Abstract

This study aims to model and predict the operating behavior of wiped film evaporators with roller wipers. A modular model has been formulated in the modeling language Modelica. The established model considers heat transfer, evaporation, fluid dynamics, and residence time behavior. It is parametrized only on the basis of operational and geometrical parameters, which makes it fully predictive. The apparatus is discretized into a series of height elements with local calculation of fluid properties, heat transfer and fluid volumes. Different heat transfer models were considered for the product side, resulting in a deviation of approximately $\pm$ 25% for the simulated heat flow. The mean residence time can be predicted with $\pm$ 40% compared to experimental results for medium to high flow rates and moderate evaporation ratios. The shape of the simulated residence time distributions generally matches well with the experimental data. Greater deviations at higher evaporation ratios were attributed to possible de-wetting of the heated surface. The model can be used to predict the influence of the main operational parameters and provides a good basis for the design and re-evaluation of wiped film evaporators. Furthermore, it allows valuable insights into the underlying physics of wiped film evaporators. The model may also be adapted to other wiper geometries by modifying some of the included empirical equations.