Cavern Development of Pseudoplastic Fluids Stirred by Impeller of Perturbed Six-bent-bladed Turbine

Abstract

The prediction of the cavern size is important in the mixing of shear-thinning fluids with yield stress.The cavern development of xanthan gum solutions,a pseudoplastic fluid with yield stress,stirred by a impeller of perturbed six-bent-bladed turbine was numerical researched using computational fluid dynamics(CFD).The cavern boundary velocity is properly determined and the cavern dimensions of shape,diameter and height to diameter ratio are obtained versus apparent Reynolds number,Re*.In order to determine the capability of CFD to forecast the flow process,the agitational experiment is used to measure the power consumption.The results show that the power data predicted by the simulation are in good agreement with those measured in the experiment,which validate CFD model developed in laminar flow.The cylindrical cavern development is found as Re* increased,which shows a good agreement with the representation of the cylindrical model(Elson’s model).The variations of dimensionless cavern diameter(Dc/D) verse dimensionless NpRey,as well as cavern height to diameter ratio,have nothing to do with the rheological index of fluids all together.CFD simulation predicts a linear slope of 0.35 from a log-log plot of Dc/D verse NpReyat DcT,which agrees well with the theoretical value,0.33,of Elson’model.The height to diameter ratio is 0.68 until the cavern reaches the tank wall,while the rate constant of axial fluid expansion describing cavern height once the cavern touched the vessel wall,β is 0.79.The research results promote the understanding of the mixing performance of the impeller of perturbed six-bent-bladed turbine and provide valuable instructions and references for the design,application and development of new type impeller in pseudoplastic fluids.