Two-phase flow in narrow channels
Two-phase flow in narrow channels with hydraulic diameters of a few millimeters are relevant for micro reactors and structured reactors, compact heat exchangers, micro condensation units or fuel cells due to the low heat and mass transfer resistance between the fluidic layers.
The Taylor flow is a beneficial flow regime due its intensive gas-liquid contact at the interface of the film surrounding the Taylor bubbles and due to the enhanced mixing in the liquid slugs downstream the Taylor bubbles.
Knowledge of the flow topology and precise measurement of liquid film thickness and Taylor bubble shape at microscopic length scales are of primary importance for the development and validation of interface resolving computational flow simulation tools.
These allow developing transport models and proposing process intensification concepts. Further objectives cover the scale-up and design of large-scale applications and related technological aspects such as to ensure homogeneous phase distribution in multi-channel configurations in order to obtain a better overall process understanding.
Current research activities comprise:
X-ray tomographic analysis of Taylor bubble shape in small channels (Taylor bubble benchmark)
Liquid flow with Taylor bubbles are characterized by an intensified gas-liquid contact in the liquid film surrounding the Taylor bubbles and by an enhanced mixing in the liquid slugs downstream the Taylor bubbles. To disclose the three-dimensional shape of Taylor bubbles in small channels, enhanced X-ray radioscopic and X-ray tomographic measurement techniques were developed and qualified. These techniques provide benchmark validation data numerical flow models.
Mass transfer in small channels and process intensification concepts
Integral and local mass transfer for Taylor flow in channels with different diameters as well as different shapes and roughness can be achieved 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. 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.
Two-phase flow in ceramic monoliths
An intensification of heterogeneous catalytic reaction processes can be achieved by monolithic structures operated in the Taylor flow regime. To benefit from the excellent gas-liquid mass transfer behavior and tunable residence time of the Taylor flow regime in monolithic structures, homogeneous and well defined gas-liquid distribution patterns are required. A new methodology to evaluate the impact of flow maldistribution from the targeted process configuration using the ultrafast electron beam X-ray modality and a pseudo 2D reactor model is proposed.