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1

Axial thrust in a vessel with unsteady rotating axial impeller

Woziwodzki Szymon

Chemical and Process Engineering : New Frontiers

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2023

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Vol. 44, nr 2

art. no. e11

EN

Unsteady motion of the impeller is one of the several methods to improve mixing in unbaffled vessel. It is very important in pharmaceutical industry, crystallization processes or some chemical reaction with catalyst where baffles are not recommended. The literature data shows that unsteady mixing cause generation of axial flow for radial impellers (Rushton turbine). The purpose of this study was to investigate axial force for axial impellers like A315, HE-3 and SC-3. Moreover, the momentum number, flow number and pumping efficiency were analysed. Results shows that axial force for unsteady mixing is higher in comparison to steady-state mixing. Also, the comparison of axial force between impellers shows that blades influence momentum number and flow number. Impellers with larger blade surface generate stronger axial force. The obtained results reveal that unsteady mixing with axial impellers could be apply for solid-liquid mixing as suitable alternative to steady-state mixing.

2

Effect of impeller shape on solid particle suspension

Rieger F., Jirout T., Ceres D., Seichter P.

Chemical and Process Engineering

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2013

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Vol. 34, nr 1

139--152

EN

This paper deals with the effect of impeller shape on off-bottom particle suspension. On the basis of numerous suspension measurements, correlations are proposed for calculating the just-suspended impeller speed for a standard pitched four-blade turbine and three types of hydrofoil impellers produced by TECHMIX for several particle sizes and for a wide range of particle concentrations. The suspension efficiency of the tested impellers is compared with the efficiency of a standard pitched blade turbine on the basis of the power consumption required for off-bottom suspension of solid particles. It is shown that the standard pitched blade turbine needs highest power consumption, i.e. it exhibits less efficiency for particle suspension than hydrofoil impellers produced by TECHMIX.

3

Replay to Comments on Flow characteristics of axial high speed impellers

Fort I.

Chemical and Process Engineering

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2012

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Vol. 33, nr 2

317-318

EN

The comments made by Professor Joshi are a most welcome addition to the findings presented by us (Fort et al., 2010). We agree that many valuable studies in the past dealt with experimental investigation of turbulent velocity field in stirred systems with axial high-speed impellers. Therefore it would be highly desirable to present a comprehensive comparison of the efficiency of various types of impellers, especially for their optimum design for processes in chemical and biochemical industries. Nevertheless in such a comparison it should be taken to consideration the quality and reliability of experimental data, because both chosen experimental techniques and selected independent variables (position of impeller, viscosity and density of agitated liquid, etc.) have to be well defined and comparable in all investigated stirred systems.

4

Comments on Flow characteristics of axial high speed impellers

Joshi J.B.

Chemical and Process Engineering

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2012

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Vol. 33, nr 2

311-315

EN

Fort et al. (2010) have written another useful article on flow characteristics generated by axial high speed impellers. I agree with the authors that the knowledge of flow patterns is crucial for developing reliable design procedures for instance, for mixing and blending (Baldyga and Bourne, 1997; Nienow, 1997; Ranade et al., 1991), for solid suspension (Raghva Rao et al., 1988; Zwietering, 1958), for gas induction (Joshi and Sharma, 1977) and bioreactions where controlled shear is important (Joshi et al., 1996). With this context, the work of Fort et al. (2010) needs some clarification and further extension.

5

A study on blending characteristics of axial flow impellers

Fort I., Jirout T.

Chemical and Process Engineering

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2011

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Vol. 32, nr 4

311-319

EN

This paper presents an analysis of the blending characteristics of axial flow high-speed impellers under a turbulent regime of flow of an agitated low viscosity liquid. The conductivity method is used to determine the time course of blending (homogenisation) of miscible liquids in a pilot plant fully baffled mixing vessel, and a torquemeter is used for measuring the impeller power input in the same system. Four-blade and six-blade pitched blade impellers and three high efficiency axial flow impellers are tested for the given degree of homogeneity (98%). The experimental results and also the results of the authors' previous study, in accordance with the theoretical approach described in the literature, show that there is a universal relationship between the impeller power number and the dimensionless blending time, taking into consideration the impeller-to-vessel diameter ratio, independent of the geometry of the axial flow impeller but dependent on the degree of homogeneity. This relationship is found to be valid on a pilot plant scale under a turbulent flow regime of an agitated liquid.

6

Numerical simulation ob three-dimensional viscous flow in an isolated axial rotor.

Corsini Alessandro, Rispoli Franco

Archive of Mechanical Engineering

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1999

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Vol. XLVI, nr 4

369-392

EN

A finite element based Navier-Stokes solver is applied to investigate the three-dimensional viscous flow in a low speed isolated axial rotor with tip clearance at design condition. A higher order anisotropic eddy viscosity model is used for closure, with wall function treatment able to simulate stationery and moving boundaries. The presented comparisons with experimental data include three-dimensional flow structure behind the rotor as well as the tip leakage flow behaviour developing through the rotor. It is shown that the code predicts well the flow structure observed in the experiments. A critical discussion of predicting limits as also carried out in order to address possible improvements.

PL

Rozwiązanie Naviera-Stockesa, oparte na metodzie elementów skończonych, zastosowano do badań trójwymiarowego przepływu lepkiego w wolnoobrotowym izolowanym wirniku osiowym ze szczeliną między szczytem łopatek i obudową, w warunkach projektowych. Zastosowano anizotropowy wirowy model lepkościowy wyższego rzędu, w którym funkcja opisująca ograniczenia ścian może reprezentować zarówno ograniczenia stacjonarne, jak i ruchome. Przedstawione w pracy porównania z danymi doświadczalnymi obejmują zarówno trójwymiarową strukturę przepływu poza wirnikiem, jak i powstającego w wirniku przepływu w wyniku upływności przez szczlinę szczytową. Jak pokazano, zastosowane oprogramowanie pozwala dobrze przewidziec strukturę przepływu obserwowaną eksperymentalnie. Przeprowadzono także krytyczną dyskusję granicznych możliwości takiego przewidywania, w celu wskazania potrzebnych ulepszeń metody.