Blend Time Measurement in the Confined Impeller Stirred Tank

Abstract

An image processing technique is applied to measure the blend time in a confined impeller stirred tank (CIST). An acid-base reaction is used to track mixing. The blend time is defined as the time taken to 95 % or 99 % of the pixels change color from purple to yellow. Six sets of impellers are employed: Rushtons, A310s, pitched-blade turbines (PBTs; three different combinations of up-and downpumping), and Intermigs. Variation of the Reynolds number Re showed that the blend time becomes shorter with increasing Re and longer with higher viscosity. As Re drops below 225, compartmentalization becomes apparent and the decolorization percentage increases suddenly when the acid reaches each communication point between the impellers.

Chemical and Process Engineering

“…Liquid mixing time is a frequently used parameter to compare mixing characteristics provided by different impellers. The advantages and limitations of the available experimental techniques for its determination, that include global and local methods, are generally well known (Jairamdas et al, 2019). One of the simplest local and non-intrusive techniques is based on Electrical Resistance Tomography (ERT) that is being increasingly adopted for the investigation of single-phase and multi-phase stirred tanks, as well as for a number of different operations of the chemical industry (Sharifi and Young, 2013).…”