Flow characteristics of differently sized Lagrangian Sensor Particles in a 15,000 l bioreactor
Creators: name: Brouwers, Isabel Sophie
Publisher: name: TUHH Universitätsbibliothek
Year: 2024
Subjects: subject: Lagrangian Sensor Particles, Pressure Sensor, Circulation Time Distribution, Lagrangian Regime Analysis, Global Mixing Time
classificationCode: 660
subject: Chemical Engineering
subject: FOS: Chemical engineering

description: In the industry, process parameters are monitored using fixed sensors mounted at the reactor wall. However, this Eulerian approach provides barely detailed insights and information about the mixing performance, which is crucial for productivity in bioprocesses. In contrast, the Lagrangian approach focuses on Lagrangian Sensor Particles (LSPs) in the moving fluid exhibiting an appropriate flow-following behavior mimicking a cell. As demonstrated in previous studies, they can be equipped with multiple process parameter sensors such as temperature, pH, dissolved oxygen or pressure. This thesis addresses three key aspects: the hydrodynamic characterization of a single-phase 15,000 L bioreactor with a pitched blade impeller and Rushton Turbine setup by means of LSPs, the comparison of two LSP sizes regarding their flow-following behavior, and the determination of differently mixed regimes within the reactor, known as compartments. LSPs with two different diameters, 40 mm (LSP40) and 60 mm (LSP60), equipped with a pressure sensor, are investigated in this study. The experiments are carried out at five different impeller frequencies. Based on measured pressure data, the axial probability of presence over the reactor height, axial velocities, circulation times, and selected circulation time distributions are analyzed to further ascertain axial compartments and, consequently, conduct a Lagrangian regime analysis. Additionally, the overall circulation times of both LSPs are compared to global mixing times in the same setup. The estimated Stokes number for the LSP40 and LSP60 are 0.21 and 0.32 for the meso-scale and 0.002 and 0.004 for the macro-scale, respectively. Hence, for the macro-scale a flow-following behavior is assumed, as it results in St ≪1. The hypothesis of the LSP60 having a bigger inertia than the LSP40 is experimentally shown in the probability of presence and the Lagrangian velocity analysis. Furthermore, the overall circulation times of LSP60 are up to 1.4 times lower than those of LSP40. As LSP60 exhibit velocities in the same range as the LSP40, this indicates that LSP60 follow shorter circulation loops. Circulation time results reveal three compartments within the reactor, which boundaries are assumed above the pitched blade impeller and below the Rushton Turbine. According to these results, the Lagrangian regime analysis shows that the middle compartment exhibits a broad residence times distribution. In contrast, the top and bottom compartment show less probability for higher residence times. At least three circulation loops within the reactor are estimated, as seen in the CTD displaying a trimodal distribution for the horizontal plane below the PB. Similarly to literature statements and confirming the latter, the ratio of the examined global mixing time to overall circulation time is between 3 and 4. This thesis emphasizes the potential and broad applicability of LSPs to gain insights into mixing processes solely through pressure data. This research underscores that the used LSP40 are more likely to discover a flow-following behavior on the meso-scale, especially for higher impeller frequencies.