Abstract
This paper presents a technique for predicting the mixing time in a high-viscosity liquid mixing system where molecular diffusion is occurring in the mixture. In the technique, the diffusion differential equation and the model equation representing the decrease in scale of segregation with time are solved simultaneously. However, prior to prediction of the mixing time, the diffusion coefficient of the solute in the bulk liquid and the cycle time distribution of liquid in a mixer must be determined. From the concentration profile obtained by the technique proposed in this work, the macroscopic mixing time is predicted as the elapsed time until the local maximum concentrations of the solute become less than a chosen arbitrary criterion of mixing. Mixing experiments were carried out for helical screw/draft tube mixers and helical ribbon impeller mixers using corn syrup and PVA solutions of various viscosities. The mixing time was determined experimentally as the elapsed time until the segregation of tracer becomes uniform. The predicted mixing times were in good agreement with those determined experimentally.
