Contact

Mohammadreza Haghnegahdar
Experimental Thermal Fluid Dynamics
m.haghnegahdarAthzdr.de
Phone: +49 351 260 - 3767

Dr. Markus Schubert
Experimental Thermal Fluid Dynamics
m.schubertAthzdr.de
Phone: +49 351 260 - 2627
Fax: +49 351 260 - 2383

Mass transfer in small channels and process intensification concepts

Micro- and mini-structured devices are of particular interest for reaction as well as heat and mass transfer in the process engineering area. For two-phase operation, the Taylor flow is a preferable flow regime, where high gas-liquid mass transfer and well defined residence times can be achieved.

The project aims at integral and local mass transfer for Taylor flow in channels with different diameters ranging from 0.5 mm to 10 mm as well as different shapes and roughness via reduction of bubble volume over time. In particular, the effect of surfactants on mass transfer is clarified and explained by analyzing interface surfactant concentration and surface tension locally.

The dissolution rate of single immobilized CO2 Taylor bubbles into water was unceasingly monitored using microfocus X-ray radiography and tomography techniques. The liquid-side mass transfer coefficient is calculated by measuring the change in the size of the bubble at constant pressure and correlated in terms of a modified Sherwood number.



The presence of surfactants causes a change of the bubble shape with slightly increased film thickness and bubble elongation. The addition of surfactants decreases the dissolution rate of small bubbles until a high bubble surface coverage ratio is reached.

In addition, a new concept for mass transfer intensification in small channels was studied using low-frequency horizontal vibrations of the mini-channel operated with freely rising Taylor bubbles in stationary water.



Bubble size and dissolution rate were determined from microfocus X-ray radiographs and the liquid-side mass transfer coefficient was calculated from the shrinking rate. The rise velocity of the bubbles and the surface wave motion were analyzed using a videometric technique. The comparison of the results for the stationary and the oscillating channel showed that mechanical vibration of the channel is able to enhance the mass transfer coefficient from gas to the liquid phase by 80 % to 186 %, depending on frequency and amplitude of the vibration, which is mainly attributed to the development of propelling surface waves and to the increase of the liquid film flow rate. Furthermore, analyzing the surface wave motion of the bubbles revealed that the enlargement of the contact area between the phases and the increased mixing enhance the mass transfer additionally up to 30 % compared to non-agitated bubbles of similar Péclet number.

Cooperation

  • TU Darmstadt,
  • RWTH Aachen,
  • TU Hamburg-Harburg,
  • TU Dresden

Funding

Deutsche Forschungsgemeinschaft (DFG, HA3088/7–1)

References



Contact

Mohammadreza Haghnegahdar
Experimental Thermal Fluid Dynamics
m.haghnegahdarAthzdr.de
Phone: +49 351 260 - 3767

Dr. Markus Schubert
Experimental Thermal Fluid Dynamics
m.schubertAthzdr.de
Phone: +49 351 260 - 2627
Fax: +49 351 260 - 2383