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Item type:Publication, Access status: with files , An experimental study on the time dependence of diffusive mass transfer of single oxygen bubbles(Elsevier, 2026-12-15); ; ; ; In the vast majority of gas–liquid engineering applications, the liquid phase contains a range of dissolved gaseous species. These dissolved process gases transfer from the liquid phase to the gaseous phase countercurrent to the typically desired mass transfer of gas to liquid. In process design, the resulting change in the composition of the gaseous phase is usually neglected, although a temporal change in the composition of the gaseous phase can directly influence the mass transfer performance over time. The current fundamental study quantifies the mass transfer performance of oxygen bubbles to liquid phases saturated with another gas. For this purpose, the oxygen mass transfer from a bubble to degassed, helium-, nitrogen-, argon- and carbon dioxide-saturated water is studied. Light Sheet Fluorescence Microscopy is used as imaging system for Planar Laser-induced Fluorescence measurements of dissolved oxygen concentration fields, delivering local instantaneous Sherwood numbers, diffusion coefficients and mass transfer coefficients. For the first time, the study showcases that the mass transfer performance from a gaseous dispersed to a liquid continuous phase is independent of time if mass transfer occurs in one direction only. If mass transfer occurs in both directions, the mass transfer performance of the dispersed phase is significantly lower and its time dependence higher to liquids containing gaseous species with high solubilities, such as carbon dioxide in water. Furthermore, the results suggest that applying intrinsic values, such as diffusion or mass transfer coefficients, obtained for binary systems in multicomponent systems can lead to high uncertainty.Publicationtype: Journal Article76 19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Experimental studies on microscopic, multiphase transport phenomena: novel applications of light sheet fluorescence microscopy(Springer Science and Business Media Deutschland GmbH, 2026-05-26); ; ; ; Over the past two decades, light sheet fluorescence microscopy has developed to a powerful tool for studies of dynamics in biological systems. In a new development, we apply light sheet fluorescence microscopy as a novel experimental measurement technology within the field of multiphase process engineering and fluid dynamics. The technology enables a number of novel studies of single- and multiphase transport phenomena on a microscopic scale. In the current publication, we introduce the first implementation of light sheet fluorescence microscopy in the field and demonstrate its applicability on one exemplary measurement of diffusive oxygen mass transfer from an oxygen bubble to degassed water. The results prove that such measurements can be conducted with a high spatial resolution with a submicron pixel pitch and enable precise studies on microscopic transport phenomena. Besides measurements of mass transfer, on which we lay the focus here, light sheet fluorescence microscopy further enables studies of fluid dynamics on a microscopic scale.Publicationtype: Journal Article75 16 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Intensification of a biocatalytic oxidation under fine bubble aeration in a rotating bed reactorThe utilization of oxidases suffers from insufficient oxygen availability due to its low solubility in gas-liquid multiphase systems. To overcome this limitation, oxygen is continuously supplied to the reaction medium during the course of the reaction, however, it causes significant gas consumption. In this study, a novel experimental set-up was established by installing a sintered frit porous sparger in the SpinChem® rotating bed reactor. Covalently immobilized glucose oxidase on epoxy-functionalized carriers was used in the rotating bed reactor with an activity yield of the immobilization of over 98%. For fine bubble aeration, the volumetric mass transfer coefficient kLa (67.3 h−1) tripled compared to macrobubble aeration (22.5 h−1), while the volume-specific aeration rate remained constant. A maximum reaction yield of 96.5% was reached. The reaction rate was improved by a factor of 12.9 for the fine bubble aeration compared to macrobubble aeration under identical conditions. With fine bubble aeration, the oxygen consumption was reduced by 87.5% over macrobubble aeration, establishing the same enzyme-specific reaction rates at a comparable kLa. Validation was carried out in repetitive batches, achieving the same glucose oxidase specific activity. This study demonstrates the advantages of fine bubble aeration and presents promising results for addressing the sustainable biotransformation processes.Publicationtype: Journal Article21 23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Advances in Characterization of Industrial Bioreactors for Cell Culture Process(Springer, 2023); ; ; ; Aerated stirred tank reactors are widely used in the biopharmaceutical industry for cell culture applications due to their flexibility and broad range of uses. This book chapter provides an overview of the main characterization methods for aerated stirred tank reactors in the context of cell culture processes. The methods described include mechanical power input, volumetric mass transfer, flow field, and mixing characterization. Examples are given using stirred tank reactors of different scales, ranging from a 3 L laboratory scale to a 15,000 L industrial scale. The chapter also discusses recent developments in the use of mobile, encapsulated sensors known as Lagrangian Sensor Particles (LSP) for continuous data collection and transmission throughout the entire reactor volume, providing insights from the perspective of cells during a cell culture process. Additionally, the state-of-the-art in numerical flow simulation is discussed, using aerated stirred tank reactors as an example to illustrate the challenges and opportunities offered by numerical flow simulation. It is highlighted that the methods described are specifically focused on cell culture applications, which have lower specific power inputs and aeration rates compared to other types of applications such as microbial fermentations or chemical reactions. The chapter also provides a brief overview of the fundamentals of aerated stirred tank reactors, including their design and components, and emphasizes the importance of equipment characterization for successful process transfer and scale-up in cell culture processes.Publicationtype: Book part59 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Unsteady mass transfer in bubble wakes analyzed by Lagrangian coherent structures in a flat-bed reactor(Multidisciplinary Digital Publishing Institute (MDPI), 2022-12-13); ; ; ; To increase the yield and selectivity in reactive bubbly flows, the gas-liquid interactions have to be understood in depth. In the current fundamental study, flow and concentration data of the wakes of two-dimensional bubbles in an organic solvent are obtained experimentally in a flat-bed reactor. The unsteady mass transport phenomena in these turbulent wakes of two freely rising, two-dimensional bubbles with bubble Reynolds numbers (Formula presented.) and (Formula presented.) are evaluated by analyzing Lagrangian Coherent Structures (LCS). To reveal how LCS govern the transport of dissolved gas in bubble wakes, and therefore affect gas-liquid reactions, LCS in two-dimensional velocity fields are computed and compared with concentration fields of dissolved gas. The analysis of backward Finite Time Lyapunov Exponent (bFTLE) fields reveals coherent fluid dynamic structures for both bubble Reynolds numbers studied. In the higher bubble Reynolds number case, two types of coherent structures are found, which hinder the mixing of the dissolved gas and the liquid bulk. Repelling LCS are found to enclose parcels transported into the vortices, and indicate thus, which fluid parcels can possibly take part in chemical reactions. Due to higher mixing, unveiled by details from the LCS and FTLE analyses, and therefore increased contact area between dissolved gas and fresh liquid, higher yields of reaction products are suggested for the lower bubble Reynolds number case in this two-dimensional study. This is contradicting the rule of thumb that mixing increases for higher bubble Reynolds numbers.Publicationtype: Journal Article68 99