Spatially resolved experimental analysis and modeling of mass transfer from rising gas bubbles under the influence of swarm turbulence with superimposed chemical reaction (DFG SPP 1740)
The SPP 1740 aims to describe the mass transport of rising gas bubbles quantitatively, based on experimentally gained local data. In the current project phase, an NMR spectrometer will be used to measure concentration and velocity distributions of single bubbles.
Photography of the experimental setup. The slide is placed inside the gradient tube of the MRI tomograph. In this, a strong magnetic field orients the nuclei of the sample. Due to this excitation, the sample emits a signal which can be detected by a set of measurement coils. The coils can be moved against each other to trim the signal detection. Cylindrical glass capillaries are used as measurement volume in which the multiphase liquid flows.
Superposition of the volumetric measurement and a model of the capillary. We measured a static phantom, which consists of a cylindrical capillary (I.D. 5mm) filled with water and air. The acquisition time is approx. 12 minutes. The color shows the intensity of the measured water signal while gray represents medium intensity. Coloured areas represent a change in thickness of the liquid layer and could indiciate inhomogeneities of the measurement. Clearly, the top part of the capillary contains trapped air, which is obvious because the water intensity signal is zero.
Comparison of different parameters during a fast imaging measurement sequence. The exposure time of each single image was approx. 50 ms with a 1 second distance between each frame. a) With a spin deflection angle of 60°, the relaxation time of the spin is larger than the time between two frames. This causes a saturation of the signal and a decrease in intensity with measurement progression. b) When the spin deflection is decreased to 10°, the saturation can be reduced. c) An additional measurement of the T2 signal gives high resolution information but also causes artefacts which can only be reduced using sequence optimization.
To quantify the influence of chemical reactions onto the mass transport of single bubbles under laminar flow onditions, an imaging method, based on the NMR spectrometer, will be developed. It will give insight into velocity distributions and flow profiles inside the wake of the bubble. Therefore a single bubble is held in place using a counter flow. The position of the bubble is determined by an array of optical fibers and controlled by adjusting the flow rate.
Maintaining laminar and homogeneous flow conditions of the counter flow is crucial. At first, the experimental setup needs to be planed and constructed. The complete setup needs to fulfill the hydrodynamic, as well as the MRI requirements.
The MRI can detect the used chemicals due to their different magnetic properties. Experiments regarding the mass transport will use a ferrous system (Fe-NO) whereas a copper system (Cu-O2) is used for experiments regarding the selectivity.
The obtained data is used to correlate and describe the mass transport of rising single bubbles. Furthermore, the data might be transferrable to bubble swarms.
Publications from the project
Helmers et al. (2022). Experiments in Fluids 63, 5. https://doi.org/10.1007/s00348-021-03358-6
Kemper et al. (2021) in Reactive Bubbly Flows, p. 137-162. https://doi.org/10.1007/978-3-030-72361-3_8
Kemper et al. (2021), Chemical Engineering & Technology 44(3), 456-476. https://doi.org/10.1002/ceat.202000509
Helmers et al. (2020) Experiments in Fluids 61(2), 64. https://doi.org/10.1007/s00348-020-2892-1
Helmers et al. (2019), Fluids 4(3), 162. https://doi.org/10.3390/fluids4030162
Kemper, Philip, M. Sc.
Room UFT 2100
Fon 0421- 218 - 63466
DFG Priority Program Reactive bubbly flows (SPP 1740)
In-vivo MR group