Analysis of residence time distribution in the extrusion process including the effect of 3‐D circulatory flow

Abstract

Abstract It is of great importance to accurately measure or predict the Residence Time Distribution (RTD) in designing extruders and/or in setting up a proper operating condition, because chemical reactions depend significantly on the RTD and temperature when chemical reactions take place during the extrusion process. A previous method to predict the RTD can analytically determine RTD, Residence Time Distribution Function f ( t ) and Cumulative Residence Time Distribution Function F ( t ), based on a simplified two‐dimensional velocity field in an extruder. However, this previous method cannot accurately take into account the three‐dimensional circulatory flow inside the extruder. The present paper suggests a new method to accurately determine the RTD taking into account the three‐dimensional circulatory flow and presents a new formula derived to calculate f ( t ). In order to demonstrate the applicability of the new method including the circulatory flow effect, RTD, f ( t ) and F ( t ) were calculated based on a three‐dimensional velocity field obtained via a quasi‐three‐dimensional finite element analysis. It was found that the previous method has a tendency to underestimate the RTD, owing to the neglect of the three‐dimensional circulatory flow in comparison with the new method.