# Strain Mode of General Flow: Characterization and Implications for Flow Pattern Structures

## TL;DR

This paper introduces a new measure to characterize the modes of strain rate in mixer flows, linking flow pattern structures with mixer geometry to improve understanding and design of mixing devices.

## Contribution

It develops a novel measure for strain rate modes in general flow, enabling detailed analysis of flow pattern structures in different mixer geometries.

## Key findings

- Flow pattern differences between conveying screws and kneading disks are characterized.
- Distribution of volumetric strain rate correlates with flow pattern structures.
- The measure aids in understanding the relation between flow patterns and mixer geometry.

## Abstract

Understanding the mixing capability of mixing devices based on their geometric shape is an important issue both for predicting mixing processes and for designing new mixers. The flow patterns in mixers are directly connected with the modes of the local strain rate, which is generally a combination of elongational flow and planar shear flow. We develop a measure to characterize the modes of the strain rate for general flow occurring in mixers. The spatial distribution of the volumetric strain rate (or non-planar strain rate) in connection with the flow pattern plays an essential role in understanding distributive mixing. With our measure, flows with different types of screw elements in a twin-screw extruder are numerically analyzed. The difference in flow pattern structure between conveying screws and kneading disks is successfully characterized by the distribution of the volumetric strain rate. The results suggest that the distribution of the strain rate mode offers an essential and convenient way for characterization of the relation between flow pattern structure and the mixer geometry.