Dr.-Ing. Felix Kexel

Eißendorfer Str. 40

Building O, Room 1.008

21073 Hamburg

Phone +49 40 42878 - 4663

Mail Felix Kexel


How are the different timescales of fluid dynamic mixing, mass transfer and reaction kinetics impacting the yield and selectivity of competitive-consecutive gas-liquid reactions?

Applying measuring techniques as Particle Image Velocimetry (PIV), Particle Tracking Velocimetry (PTV), Laser Induced Fluorescence (LIF) or imaging UV-VIS Spectroscopy to obtain information on velocity and concentration fields around reactive bubbles to understand the complex interplay of fluid dynamics, mass transfer and chemical reactions.

Research Projects
  • Mixing structures in bubble wakes of single bubbles and bubble swarms and their influence on gas-liquid mass transfer and chemical reaction

  • I3 Junior Project in collaboration with Hannah Buchholz (IPI) and Dr.-Ing. Jürgen Fitschen funded by the TUHH: Tomographic Reconstruction of Spherical and Irregularly Shaped Bubbles for Precise Determination of the Interfacial Area

  • DFG Priority Project 1740 – Reactive Bubbly Flows


Undergraduate courses

  • Fundamentals of Fluid Mechanics (Fluid Mechanics I)

Supervised Theses

  • "Design of a transparent MRI ready setup for the determination of bubble surfaces" [working title], Ole Simmering, Master thesis, in collaboration with Hannah Buchholz (IPI)

  • "Vergleich von Strömungs- und Konzentrationsfeldern in einem Flachbettreaktor mittels Particle Image Velocimetry und Laserinduzierter Fluoreszenz", Rene Weglewski, Master thesis, 2023

  • "Experimentelle Untersuchung von Konzentrations- und Strömungsfeldern im Nachlauf einer reaktiven Taylor Blase", Anahita Radmehr, Master thesis, 2023

  • "Experimentelle Untersuchung der 3–dimensionalen Strömungsstrukturen in einer Blasenströmung mittels 4D–PTV", Yara Kappes, Master thesis, 2022

  • "Taylor Bubbles in Organic Solvents", Sina Bertram, Bachelor thesis, 2022

  • "Computation of Unsteady Mass Transfer in Bubble Wakes by Means of 2D Lagrangian Analysis", Lotta Kursula, Master thesis, 2022

  • "Anwendung der Penetrationstheorie auf lokale Stofftransportprozesse an Taylor Blasen", Benjamin Rahimian, Bachelor thesis, 2022

  • "Characterization of the fluid dynamic properties of a Methanol based chemical reaction", Noah von Schnitzler, Bachelor thesis, 2021

  • "Taylor Bubble Generation Using a Solenoid Valve", Tarlan Ramazanli, Project Work 2021

  • "Detailed investigations of bubble trajectories in clean and contaminated systems", Sam Dors, Bachelor thesis, 2020

  • "Determination of mass transfer coefficients from single Taylor bubbles in contaminated systems – a study for industrial applications", Aaron Kaulbarsch, Bachelor thesis, 2019

  • "Experimentelle Analyse des Einflusses von organischen Lösemitteln auf die Hydrodynamik von Taylorblasen am Bespiel von Acetonitril", Carolin Lohmann, Bachelor thesis, 2019

Oral and Poster Presentations


  • Fitschen, J.; Kexel, F.; Hofmann, S.; Kuschel, M.; Hoffmann M.; Wucherpfennig, T.; Schlüter, M.:" Hydrodynamic Characterization and Identification of Heterogeneities in Stirred Tank Reactory by Means of 4D Particle Trajectories", 11th International Conference on Multiphase Flows, Kobe, Japan, 2023, oral presentation

  • Radmehr, A; Kexel, F.; von Kameke, A.; Hoffmann, M.; Schlüter, M.: "Local Velocity Fields at Taylor Bubbles in Methanol" 11th Workshop Chemical and Biological Mico Laboratory Technology 2022, Ilmenau, 2022, oral presentation

  • Kexel, F.; von Kameke, A.; Hoffmann, M.; Schlüter, M.: "Fluid Dynamics of Taylor Bubbles in Organic Solvents" ProcessNet Jahrestreffen Mehrphasenströmungen, Mechanische Flüssigkeitsabtrennung & Zerkleinern und Klassieren 2022, virtual, 2022, oral presentation

  • Kexel, F.; von Kameke, A.; Hoffmann, M.; Schlüter, M.: "Investigation on Velocity and Concentration Fields at Taylor Bubbles in a Reactive Bubbly Flow" Dispersed Two-Phase Flows 2021, virtual, 2021, oral presentation

  • Kexel, F.; von Kameke, A.; Hoffmann, M.; Schlüter, M.: "Influence of Fluid Dynamics on the Selectivity of Competitive Consecutive Gas Liquid Reactions" 13th European Congress of Chemical Engineering (ECCE13), virtual, 2021, oral presentation

  • Kexel, F.; von Kameke, A.; Colombi, R.; Rüttinger, S.; Hoffmann, M.; Schlüter, M.: "Inverstigation of Reactive Mass Transfer Processes at Single Rising Bubbles by Means of Time-Resolved Scanning Laser Induced Fluorescence" 12th European Congress of Chemical Engineering (ECCE12), Florence, Italy, 2019, oral presentation

  • Kexel, F.; Rüttinger, S.; Kastens, S.; von Kameke, A.; Oßberger, M.; Hoffmann, M.; Schlüter, M.: "Does the wake structure in bubbly flows affect yield and selectivity of a competitive consecutive reaction? – A Taylor-Bubble study" ProcessNet Jahrestreffen Reaktionstechnik & Mehrphasenströmungen 2019, Würzburg, 2019, oral presentation

Poster Presentations

  • Merbach,T.; Mockus, B.; Minamitani, K.; Kexel, F.; Schlüter, M.; Valluri, P.; Hayashi, K.; Tomiyama, A.:" Development of a Correlation for the Terminal Rising Velocity for 2D-Bubbles in Unconfined Domain", 11th International Conference on Multiphase Flows, Kobe, Japan, 2023, poster presentation

  • Kexel, F.; Bertram, S.; Merbach, T.; von Kameke, A.; Hoffmann, M.; Tomiyama, A.; Schlüter, M.: "Influence of Taylor Bubble Shapes on Wake Structures", 4th International Symposium on Multiscale Multiphase Process Engineering, Berlin, 2022, poster presentation

  • Kexel, F.; von Kameke, A; Hoffmann, M.; Schlüter, M.: "Optimization of Chemical Reactions with Tailored Flow Strucures" ProcessNet Jahrestreffen Reaktionstechnik 2021, virtual, 2021, poster presentation

  • Kexel, F.; von Kameke, A; Hoffmann, M.; Schlüter, M.: "Investigation of the influence of fluid dynamics on the selectivity of fast gas-liquid reactions by means of high speed imaging UV/VIS spectroscopy at a Taylor bubble setup" ProcessNet Jahrestreffen Mehrphasenströmungen & CFD 2021, virtual, 2021, poster presentation


Title: Unsteady Mass Transfer in Bubble Wakes Analyzed by Lagrangian Coherent Structures in a Flat-Bed Reactor.
Written by: Kursula, L.; Kexel, F.; Fitschen, J.; Hoffmann, M.; Schlüter, M.; Kameke, A.v.;
in: <em>Processes</em>. (2022).
Volume: <strong>10</strong>. Number: (12),
on pages:
Publisher: MDPI:
how published:
DOI: https://doi.org/10.3390/pr10122686


Abstract: 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 Re=949 and Re=388 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.