(226e) Predicting Blend Time and Mixing Efficiency of Different Types of Impellers with Mean Age Method

The mean age method is assessed to characterize impeller mixing performance of stirred tank reactors with three types of commonly used impellers in process industries: PBT, A310, and Rushton. The spatial distribution of mean age reveals the non-uniform distribution of local blend time. The mean age frequency function is found to scale with impeller speed. The function can also be scaled with the ratio of the impeller diameter to the tank diameter but the exponent of the ratio is slightly different for each type of impellers. A blend time can be defined from the mean age frequency function and this blend time is found to agree very well with the blend time correlations in literature. This method can be used to predict blend time in a stirred tank reactor using CFD with only a small fraction of the CPU time required by the current method of solving the time dependent tracer scalar equation. With this method, CFD can be efficiently used for practical reactor analysis, design, and scale-up.