Felix Kexel, M.Sc.

Eißendorfer Str. 40, Building N, Room 1.082

Telephone +49 40 42878-4663

E-Mail: Felix Kexel, M.Sc.


DFG Priority Project 1740 - "Reactive Bubbly Flows"


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

Applying measuring techniques as Particle Image Velocimetry (PIV), Laser Induced Fluorescence (LIF) or imaging UV-VIS Spectroscopy to obtain information on velocity and concentration fields of primary and secondary products in the wake of rising gas bubbles


Graduate Teaching Assistant

  • Fluid Mechanics in Process Engineering (Winter term)


Supervised Theses

Current Thesis:
  • "Experimentelle Untersuchung des Einflusses der Fluiddynamik auf eine kompetitiv-konsekutive Reaktion in einer Hele-Shaw Zelle" [Working Title], Rene Weglewski, Master thesis
Finished Thesis:
  • "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 Selonoid 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

  • Kexel, F.; Bertram, S.; Mehrbach, 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
  • 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; 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
  • 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


Title: A Novel Approach for Visualizing Mixing Phenomena of Reactive Liquid-Liquid Flows in Milli- and Micro-Channels.
Written by: Frey T.; Kexel F.; Dittmer K.R.; Bohne S.; Hoffmann M.; Trieu H.K.; Schlüter M.
in: <em>Frontiers in Chemical Engineering</em>. (2022).
Volume: <strong>4</strong>. Number:
on pages: 874019
how published:
DOI: https://doi.org/10.3389/fceng.2022.874019


Abstract: Modular milli- and micro-structured systems represent a promising approach to exploit the potential of micro-process technology, including precise reaction control and scale-up. A major drawback of micro-structured devices is fouling and mixing mechanisms need to be investigated phenomenologically to better understand the processes that lead to fouling. Previous work was conducted to resolve 3D concentration fields by means of Laser-Induced Fluorescence (LIF) using a Confocal Laser Scanning Microscope (CLSM) (Frey et al., J Flow Chem, 2021, 11, 599–609). While the CLSM-LIF method yields detailed insight into concentration fields down to a few micrometers, it is limited to stationary flow structures only. Aubin et al. (Chemical Engineering Science, 2010, 65, 2065–2093) give a comprehensive review of methods to analyze mixing behavior. Most recent optical measurement methods rely on the detection of a single compound in mixtures. In case of reactive mixing, Tthe state of the art procedures to locally visualize micro mixing relies on tracking a reaction product which forms on molecular scale. In literature, only small micro-structures are manufactured from transparent materials, however larger milli-structures often lack optical accesses with sufficient quality. Selective laser-induced etching (SLE) is a new technique which enables the fabrication of larger milli-structures in transparent materials that are relevant for industry-scale applications. This work develops a method based on a concept of Kexel et al. (Chemie Ingenieur Technik, 2021, 93, 830–837) visualizing the selectivity of a competitive-consecutive gas-liquid reaction in a Taylor bubble flow. The main goal of this work is the analysis of the absorbance spectra of bromothymol blue (BTB) at different pH values in a miscible liquid-liquid system in a fused silica split-and-recombine mixer. The milli-structure of the mixer is manufactured by means of SLE. Backlight at different wavelengths is pulsed matching the recording frequency. In contrast to conventional UV/Vis setups, the absorbance is recorded locally within the mixer. The proposed method yields the 2D concentration distribution of multiple species with high spatial resolution. The spatially resolved reactant and product distribution unveils micro mixing and can yield important information about local root causes of fouling.