Effect of time delays in characterizing the continuous mixing of non-Newtonian fluids in stirred-tank reactors

► This work compares the effectiveness of three different dynamic mixing models. ► Assumption of the equal time delays for bypassing and mixing zones was unrealistic. ► The models with two time delays gave a better match with the experimental results. ► Dynamic results obtained in discrete and continuous time domains were the same. ► Model parameters exerting strong influence on the mixing dynamics were identified. Aqueous xanthan gum solutions are pseudoplastic fluids possessing yield stress. Their continuous mixing is an extremely complicated phenomenon exhibiting non idealities such as channeling, recirculation and dead zones within the stirred-tank reactors. To characterize the continuous mixing of xanthan gum solutions, three dynamic models were utilized: (1) a dynamic model with 2 time delays in discrete time domain, (2) a dynamic model with two time delays in continuous time domain, and (3) a simplified dynamic model with a single time delay in discrete time domain. A hybrid genetic algorithm was employed to estimate the model parameters through the experimental input–output dynamic data. The extents of channeling and fully mixed volume were used to compare the performances of these three models. The dynamic model parameters exerting strong influence on the response predicted by the dynamic model were identified. It was observed that the models with 2 time delays gave a better match with the experimental results.