Study on double-shaft mixing paddle undergoing planetary motion in the laminar flow mixing system

Abstract

This article has studied the impact of double-shaft mixing paddle undergoing planetary motion on laminar flow mixing system using flow field visualization experiment and computational fluid dynamics simulation. Digital image processing was conducted to analyze the mixing efficiency of mixing paddle in co-rotating and counter-rotating modes. It was found that the double-shaft mixing paddle undergoing planetary motion would not produce the isolated mixing regions in the laminar flow mixing system, and its mixing efficiency in counter-rotating modes was higher than that in co-rotating modes, especially at low rotating speed. According to the tracer trajectory experiment, it was found that the path line of the tracer in the flow field in co-rotating modes was distributed in the opposite direction to the path line in counter-rotating modes. Planetary motion of mixing paddle had stretching, shearing, and folding effects on the trajectory of the tracer. By means of computational fluid dynamics simulation, it was found that axial flows and tangential flows produced in co-rotating and counter-rotating modes have similar flow velocity but opposite flow directions. It is deduced from the distribution rule of axial flow, radial flow, and tangential flow in the flow field that axial flow is the main reason for causing different mixing efficiencies between co-rotating and counter-rotating modes.