Charalambidou, Artemis Danae;
(2023)
An integrated numerical and experimental investigation of the flow and power consumption in scale-down bioreactors.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Optimal mixing performance is of major importance for the chemical and biochemical industries. The design of economically feasible and profitable production processes has driven companies towards optimisation of continuous manufacturing and intensification of individual operations by reducing working volumes and increasing operating frequencies. In this respect, the development of robust small scale devices capable of multivariate process optimisation is essential. The aim of this work is to characterise the flow pattern and power consumption in a 250 ml-scale stirred tank reactor (STR) operating at Re=3,732. Velocity and turbulence characteristics are computed via Computational Fluid Dynamics (CFD) and validated via Particle Image Velocimetry (PIV) for radially agitated unbaffled (UB) and baffled configurations equipped with baffles of different sizes. Trailing vortex stability is assessed with respect to baffle presence and size while the impact of the impeller disk on flow instabilities is discussed. Proper Orthogonal Decomposition (POD) and Fast Fourier Transform (FFT) are used to extract dominant spatial modes and corresponding frequencies affecting the underlying flow patterns. Results showed good agreement between CFD and PIV while POD analysis revealed the existence of highly energetic and periodic modes, linked to interactions between impeller jet and reactor walls. These modes are responsible for an impeller jet instability, which is amplified by baffle presence, size and absence of impeller disk. Assessment of power consumption across various small scale bioreactors showed that the presence of probes results in a power number rise equivalent to that produced by baffles, more pronounced in radially agitated vessels. Flow characterisation around the probes highlights that changes in probe geometry can lead to power number reduction. This study demonstrates that thorough understanding of the hydrodynamics is important for parameter optimisation when small scale reactors are tested as minor design changes can affect the flow characteristics, thus having significant implications on mixing and mass transfer performance.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | An integrated numerical and experimental investigation of the flow and power consumption in scale-down bioreactors |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2023. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Mechanical Engineering |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10166798 |
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