Intensification of chemical absorption efficiency within optimized microfluidics

In the field of chemical engineering, optimization of many processes involving gas-liquid reactions such as direct fluorination of aromatics or chemical absorption of CO2 by monoethanolamine (MEA) represent significant industrial and / or environmental issues due to increasing energy costs and global warming. The use of microfluidic devices (like mini-channels of 1 mm width) enhance the mass transfer since the surface-to-volume ratio of spherical bubbles is dramatically increased at the millimeter scale. Moreover, microfluidics enables to get rid of towers or packed columns having huge volumes, low efficiencies, higher costs and safety concerns. Furthermore, optimization of the mini-channel design enables to intensify the chemical mass transfer while keeping the pressure drop within an acceptable range. The general objective of the proposed Ph.D. thesis is to design, manufacture and test, by means of optical investigations and computational post-treatment, an optimal minichannel carrying chemical absorption of a gaseous stream into a liquid absorbent solution. First, one has to understand the fundamental transport mechanisms (two-phase flow patterns, interfacial behaviors, coupled heat and mass transfer, etc.) for chemical absorption process in mini-channels. Then, the flow/temperature/concentration fields in the minichannel absorber are characterized using optical-based high-precision measurement techniques, while the mass transfer is enhanced by the geometry and surface properties (including roughness, wettability etc.) of the walls. Secondly, the observed liquid film between the wall and the bubbles shall be investigated at shorter scales (< 100 μm) because of the significant influence of its thickness upon the overall absorption rate, as it is taken into account by models. Its thickness depends on fluid properties, the flow velocity field, and the wettability of the liquid [1]; it is often nonuniform and thicker in the corners. LEMTA has already implemented both laser-induced fluorescence (LIF) and Chromatic Confocal Line Displacement (CCLD) techniques for the investigation of thin falling liquid films [2] and considers to apply such optical diagnostics within the gas-liquid absorption process to characterize the observed liquid film, using an appropriate chemical tracer. Finally, numbering-up of a laboratory-scale miniature device enclosing parallel microchannels shall enable to demonstrate industrial efficiency of the well-controlled developed process. In this extent, some nature or bio-inspired geometries (tree-like, vascular, meshed network, etc.) and innovative, i.e. additive manufacturing will be considered for the integrated absorption device. The experimental campaign should determine suitable operating parameters for achieving the highest throughput of gas absorption, especially at the exhaust of real-world industrial pilot processes such as sorption-enhanced gasification with limestone, or regeneration of CO2 within greenhouse.

[1] Colin Butler, Emmanuel Cid, Anne-Marie Billet, Benjamin Lalanne, Numerical simulation of mass transfer dynamics in Taylor flows, International Journal of Heat and Mass Transfer, Vol. 179, 2021.

[2] R. Collignon, O. Caballina, F. Lemoine et al. Simultaneous temperature and thickness measurements of falling liquid films by laser-induced fluorescence. Experiments in Fluids, Vol. 63, 2022.

The Laboratoire de Thermocinétique de Nantes (LTN) was created in 1967 as a joint laboratory between French CNRS (INSIS) and Nantes Université. Since January 2018, it has become the LTeN (Laboratoire de Thermique et Energie de Nantes).
The LTeN has a long history in the field of Heat Transfer, wich is widely known at both the french and international level. Its detailed experimental approach is based on recognized skills and in-house methods, and on an in-depth analysis and modelisation of the physical phenomena as well. Its activities are quite balanced between fundamental research and applied technological developments.
Its activities are composed of two main topics :
- Heat transfer within materials and through interfaces : The goal is to analyse, at different scales of space and time, heat transfer within solid materials in order to control their properties that can be inhomogeneous. Numerous industrial applications are then developed in the field of material engineering.
- Heat and mass transfer within fluids and energy systems : The goal is to efficiently manage energy and heat transfer at different scales from local to the whole facility, in order to improve the overall performance of the process. For instance, temperature distribution within multi-functional heat exchangers, energy storage through Phase Change Materials (PCMs), or management of fluids within Fuel Cells are studied in the frame of sustainable development.
The LTeN included 74 people in 2020, including 30 permanent researchers and 32 Ph.D. students and post-doctoral fellows. Around 1 student is graduating their Ph.D. every year. It publishes around 30 articles in peer-reviewed international journals per year. It is located on an area of 2600 sq. meters, including 600 sq. meters of offices, 1000 sq. meters of experimental rooms, and 1000 sq. meters of storage facility.

The student (Master degree) should have skills in Fluid Mechanics, Basic programming skills, Optics and photography, Chemical engineering, image processing