Investigation of dense slurry suspensions with coaxial mixers: Influences of design variables through tomography and mathematical modelling--颗粒学报PARTICUOLOGY

Mishra, P., & Ein-Mozaffari, F. (2022). Investigation of dense slurry suspensions with coaxial mixers: Influences of design variables through tomography and mathematical modelling. Particuology, 65, 1-16. https://doi.org/10.1016/j.partic.2021.06.010

Investigation of dense slurry suspensions with coaxial mixers: Influences of design variables through tomography and mathematical modelling

Prakash Mishra, Farhad Ein-Mozaffari^*

Department of Chemical Engineering, Ryerson University, Toronto, M5B 2K3, Canada

10.1016/j.partic.2021.06.010

Volume 65, June 2022, Pages 1-16

Received 7 February 2021, Revised 27 May 2021, Accepted 14 June 2021, Available online 10 July 2021, Version of Record 22 July 2021.

E-mail: fmozaffa@ryerson.ca

Highlights

• Dispersion of solids with coaxial mixers was examined via ERT and CFD.

• Loss of energy was minimal for the system with an impeller spacing of 13.3 cm.

• Axial homogeneity enhanced with a decrease in inner impeller clearance.

• Inner stirrer diameter of 18 cm was proper to achieve better suspension quality.

• Use of inner A320 stirrer improved both axial and radial dispersion of solids.

Abstract

The coaxial mixers enhance the suspension of concentrated slurries in an agitated reactor. In this research work, the complex slurry suspension and dissemination behavior in a coaxial slurry mixing system (comprised of a close clearance anchor rotating with a low speed and an inner axial impeller rotating with a high speed) was analyzed employing ERT (electrical resistance tomography, a non-intrusive flow visualization technique), and computational fluid dynamics (CFD). The numerical models were validated by comparing the axial solid concentration profiles generated using the ERT data and the CFD simulation results. The influences of various important parameters such as the diameter of the inner axial impeller, the inner impeller type, and the inner impeller spacing on the hydrodynamic characteristics of the slurry suspensions in a coaxial mixing vessel were thoroughly analyzed. The radial and axial velocity profiles of solid particles were generated using the validated mathematical models. The assessment of energy loss due to the solid–solid collisions, the particle–fluid frictions, and the particle–vessel wall collisions was conducted. The evaluation of optimum inner impeller clearance and inner impeller diameter is essential to attain a high degree of solids suspension and dissemination in a coaxial slurry mixing system.

Graphical abstract

Keywords

Coaxial mixer; Slurry suspension; Homogeneity; Mixing index; Electrical resistance tomography (ERT); Computational fluid dynamics (CFD)

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