Title: Gaseous microfluidics: molecular tagging as an experimental tool for analyzing its particularities
Speaker: Prof. Stéphane COLIN
Affiliation: Institut Clément Ader, University of Toulouse, France
Date: Friday March 25th
***This is an online event. To obtain Zoom link and password, please contact to the department.
The last decades have witnessed a rapid development of fluidic micro-electro-mechanical systems (MEMS), among which fluidic microsystems that involve gas microflows. These microsystems require an accurate control of the flow rate and temperature, for a lot of applications: micro-heat exchangers, micronozzles for picosats propulsion, fluidic micro-actuators for active control of aerodynamic flows, mass flow and temperature micro-sensors, micropumps and microsystems for mixing or separation for local gas analysis… Following a rapid overview of these various applications, the properties of gas microflows will be introduced. Their main particularity is the local thermodynamic disequilibrium which appears first at the walls, in the so-called Knudsen layer. It is a consequence of rarefaction resulting from an increase of the Knudsen number, which represents the ratio of the mean free path over a characteristics length of the fluidic microsystem. At a macroscopic level, the thermodynamic disequilibrium observed in the Knudsen layer leads to a velocity slip and a temperature jump at the wall. Rarefaction also allows generating temperature-driven microflows which can be exploited in Knudsen micropumps. These pumps are able to operate without any moving element and are consequently very reliable: they do not require any maintenance and are adapted for use in critical environments, such as in space. Several designs will be presented and discussed. For developing efficient fluidic microsystems, new experimental tools are required to locally analyze the specific phenomena of confined rarefied flows and help developing accurate models of velocity slip and temperature jump boundary conditions. The presentation will then focus on recent developments for implementing molecular tagging techniques to analyze velocity, density and temperature fields in gaseous pressure- or temperature-driven microflows. Experimental issues are numerous and varied, and analyzing the slip-flow regime is very challenging and requires treating a series of compromises and coupling numerical and experimental analysis.
Stéphane Colin is a Professor in the Mechanical Engineering Department of the National Institute of Applied Sciences (INSA) in the University of Toulouse, France, since 2002. He obtained an Engineer degree from ENSEEIHT in 1987 and received his PhD in Fluid Mechanics from the Polytechnic National Institute of Toulouse in 1992. He created in 1999 the Microfluidics Group of the Hydrotechnic Society of France. Stéephane Colin initiated and co-chaired the series of Microfluidics French Conferences (μFlu’02 to μFlu’06) and the series of Microfluidics European Conferences (μFlu’08 to μFlu’18). His current research in microfluidics is mainly focused on gas microflows, with a particular interest in the experimental analysis of rarefied flows. He was the coordinator of the GASMEMS European Initial Training Network aimed at training young researchers in the field of rarefied gas flows in MEMS. He is the author of more than 140 scientific papers in international journals or conference proceedings and the editor or co-author of four text books. He is an Associate Editor of Microfluidics and Microfluidics and a member of the Editorial Board of Micromachines. He is currently the Head of the Modeling and Simulation of System and Microsystem Group of Institut Cl ́ement Ader, which includes the Microfluidics Research Team.