Characterisation of the mixing of non‐newtonian fluids with a scaba 6SRGT impeller through ert and CFD

Abstract

An attempt has been made to study the mixing of yield-pseudoplastic fluids with a Scaba 6SRGT impeller using electrical resistance tomography (ERT) and computational fluid dynamics (CFD). The ERT system with four sensor planes, each containing 16 equispaced stainless steel electrodes, was used to measure the mixing time. The multiple reference frames (MRF) technique and the modified Herschel-Bulkley model were applied to simulate the impeller rotation and the rheological behaviour of the non-Newtonian fluids, respectively. To validate the model, the CFD results for the power consumption were compared to the experimental data. The validated model was then employed to obtain further information regarding the averaged impeller shear rate, impeller circulation, and pumping capacities. The CFD and ERT data were utilised to investigate the effect of the impeller power, fluid rheology, and impeller size on the mixing time. The mixing time results obtained in this study were in good agreement with those reported in the literature.

Computational fluid dynamic studies of mixers for highly viscous shear thinning fluids and PIV validation

“…Other common configurations for mixing of highly viscous non-Newtonian fluids are two coaxial impellers, a central one, such as the Scabba impeller or the Rushton turbine, and an external one, such as an anchor impeller. The Scabba impeller and the Rushton turbine have similar constants: 10.5 (Pakzad et al, 2013b) and 9.6-11.5 (Cortada-Garcia et al, 2017, Patel et al, 2012, respectively. In contrast, anchor impellers have larger constants of around 23 (Pakzad et al, 2013a).…”

“…A number of studies can be found in the literature concerning these topics (see, for instance, Kazemzadeh et al, 2016, Patel et al, 2015, Stobiac et al, 2014, Pakzad et al, 2013b. These overall parameters, however, do not reveal details of the fluid dynamics and mixing patterns within the mixers, which can only be obtained with detailed flow field measurements.…”

Review of Visualization of Flow and Dispersion States of Slurry System Fluids in Stirred Vessels

“…2.2.2 ERT and other tomography measurements ERT can provide a non-intrusive technique to examine, in three dimensions, the homogeneity and flow pattern, even for opaque fluids inside a mixing tank. Pakzad et al (2008Pakzad et al ( , 2013) employed a 4-plane 16-sensor ring ERT system to study the shape and size of the cavern generated around a radial-flow Scaba 6SRGT impeller in the mixing of a xanthan gum solution, which is a pseudoplastic fluid possessing yield stress. The size of the cavern measured using ERT was in good agreement with that calculated using Elson's model noted in Section 2.1.…”

Technical Report on NETL's Non Newtonian Multiphase Slurry Workshop: A path forward to understanding non-Newtonian multiphase slurry flows

“…To overcome the numerical instabilities caused by the Herschel-Bulkley model due to very high viscosity (approaching infinity) at small shear rates, the upper end of the viscosity is constrained to a user-specified high value. Research of single phase viscoplastic fluids [22][23][24][25] has been actively pursued due to their wide usage in many industrial and biological applications and processes. This wide body of past work on viscoplastic fluids has been comprehensively reviewed in a recent review article by Balmforth, Frigaard, Ovarlez [26].…”