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Studies of a mixing process induced by a rotating magnetic field with the application of magnetic particles

Rakoczy Rafał, Kordas Marian, Markowska-Szczupak Agata, Konopacki Maciej, Augustyniak Adrian, Jabłońska Joanna, Paszkiewicz Oliwia, Dubrowska Kamila, Story Grzegorz, Story Anna, Ziętarska Katarzyna, Sołoducha Dawid, Borowski Tomasz, Roszak Marta, Grygorcewicz Bartłomiej, Dołęgowska Barbara

Chemical and Process Engineering

2021

Vol. 42, nr 2

157-–172

We demonstrate in this study that a rotating magnetic field (RMF) and spinning magnetic particles using this kind of magnetic field give rise to a motion mechanism capable of triggering mixing effect in liquids. In this experimental work two mixing mechanisms were used, magnetohydrodynamics due to the Lorentz force and mixing due to magnetic particles under the action of RMF, acted upon by the Kelvin force. To evidence these mechanisms, we report mixing time measured during the neutralization process (weak acid-strong base) under the action of RMF with and without magnetic particles. The efficiency of the mixing process was enhanced by a maximum of 6.5% and 12.8% owing to the application of RMF and the synergistic effect of magnetic field and magnetic particles, respectively

Experimental and numerical investigation of axialand tangential forces in a stirred tank with yield-stress fluids

Story Anna, Story Grzegorz, Jaworski Zdzisław

Chemical and Process Engineering

2021

Vol. 42, nr 2

173–-190

Complex rheological properties of yield-stress materials may lead to the generation of an intensive mixing zone near a rotating impeller. From the practical point of view, the zone should cover most of the stirred liquid. According to the literature review, several parameters may affect the size of the mixing zone, in particular forces exerted on the liquid. This paper presents both experimental and numerical investigation of axial and tangential forces generated during mechanical mixing of yield-stress fluids in a stirred tank. The tested fluids were aqueous solutions of Carbopol Ultrez 30 of concentration either 0.2 or 0.6 wt% and pH = 5.0. The study was performed for three types of impeller, pitched blade turbine, Prochem Maxflo T and Rushton turbine, in a broad range of their rotational speed, 𝑁 = 60 − 900 rpm. The axial and tangential forces were calculated from the apparent mass of the stirred tank and torque, respectively. The experimental results were compared with CFD predictions, revealing their good agreement. Analysis of the generated forces showed that they are dependent on the rheological characteristic of liquid and the impeller type. It was also found that although axial force was smaller than tangential force, it significantly increased the resultant force.

Effect of carbomer microgel pH and concentration on the Herschel–Bulkley parameters

Story Anna, Story Grzegorz, Jaworski Zdzisław

Chemical and Process Engineering

2020

Vol. 41, nr 3

173-–182

The article presents an experimental investigation of the rheological properties of carbomer microgels.All of the tested fluids were made up from commercial polyacrylic acid, Carbopol Ultrez 30. Intotal, eighteen microgels were prepared, differing in concentration; 0.2, 0.4 and 0.6 wt%, with sixlevels of neutralisation for pH from 4.0 to 9.0. Based on the experimental flow curves it was foundthat all tested microgels are yield stress shear-thinning fluids. Therefore, the Herschel–Bulkley modelwas used and its rheological parameters were determined. It was found that both the concentrationand the pH value significantly affected the yield stress. As the Carbopol concentration increased,the yield point also increased. With the increasing value of pH, the yield stress first increased untila certain maximum level and then decreased. The maximum values of yield stress were obtained forpH=6to 7, depending on polymer concentration. It was also found that flow curves of the testedmicrogels could be described using one universal master curve, thus they have common rheologicalbehaviour.