Stéphane Colin
Université de Toulouse, Institut Clément Ader (ICA), Faculty Member
- Stéphane Colin has been a Professor at INSA since 2002 and currently leads the Modeling of Mechanical Systems and Mic... moreStéphane Colin has been a Professor at INSA since 2002 and currently leads the Modeling of Mechanical Systems and Microsystems Group of the Clément Ader Institute. He is a specialist in Microfluidics and is particularly interested in gas microflows and their applications. He is the author of several books on microfluidics and chairs the series of “Microfluidics” international conferences he initiated in 2008.edit
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Studying the gas flows at rarefied conditions is imperative in the fields of gas sensing, micro gas heat exchangers, reentry of space vehicles etc. The last couple of decades has witnessed a considerable progress in this domain on... more
Studying the gas flows at rarefied conditions is imperative in the fields of gas sensing, micro gas heat exchangers, reentry of space vehicles etc. The last couple of decades has witnessed a considerable progress in this domain on theoretical and numerical fronts. However, there is a clear lack of extensive experimental data, and the main underlying reason is the challenging nature of experimentation at rarefied conditions. In this regard, molecular tagging technique has the potential to become a significant experimental technique in the field of rarefied gas flows. In principle, molecular tagging approaches can be used for local measurements of velocity and temperature. The former is generally referred as molecular tagging velocimetry (MTV). The latter is the focus of this study, and is referred as molecular tagging thermometry (MTT). Due to the employment of molecules as tracers emitting light once excited by a light source, there is a minimal intrusion of these molecules with the overall flow behavior. Acetone and biacetyl are generally employed as tracers by researchers for MTV applications. However, works related to the temperature dependence of these tracers luminescent properties in rarefied conditions are scarce. Therefore, in this study, a preliminary investigation is carried on the behavior of these tracers molecules at different conditions of pressure and temperature. This study will be helpful in assessing the feasibility of these molecules as molecular tracers to map temperature profiles in gaseous rarefied flows.
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A novel configuration of Knudsen pump is numerically studied in this paper. The pumping element consists of two facing isothermal ratchet surfaces at different temperatures. Since the main practical difficulty associated with traditional... more
A novel configuration of Knudsen pump is numerically studied in this paper. The pumping element consists of two facing isothermal ratchet surfaces at different temperatures. Since the main practical difficulty associated with traditional Knudsen pumps which refers to the necessity to accurately control the temperature gradient imposed along the walls of the device, the possibility of independently heating or cooling two distinct surfaces can be considered as a turnaround point in the design simplification of such new generation pumps. The micrometric dimensions of the pump provide the necessary conditions for obtaining rarefied gas inside the device and the asymmetric saw-tooth-like surfaces provide the optimal geometrical conditions in order to create temperature inequalities along the flow that finally engender a macroscopic gas movement. The rarefied flow is numerically investigated by Direct Simulation Monte Carlo (DSMC) in a large range of Knudsen number. The mass flowrate reaches a maximum value for a Knudsen number around 0.1 and becomes negative for a Knudsen number close to unity. A bidirectional flow depending on the Knudsen number value is observed and described. The temperature distributions, flow patterns and generated flow rate are investigated for different Knudsen numbers and also with different accommodation coefficients on vertical and inclined walls of the ratchet surfaces. The results are sensitive to the local boundary conditions.
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Research Interests: Microfluidics, Gas Sensors, Kinetic Theory, Microfabrication, Microchannels, and 15 moreDSMC, FE Analysis, Compressibility, Measurement and Control, Analytical Solution, Miniaturization, Electronic cooling, Benzene, Micro Mixer, Computational Fluid Dynamics CFD, Heat Sinks, Capillary Tubes, BTEX, Microfluidic, and Gas mixtures
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The temperature driven rarefied gas flow and the pressure difference associated to this phenomenon have been numerically studied for the specific case of a multistage pump assembly consisting of a series of channels with linearly... more
The temperature driven rarefied gas flow and the pressure difference associated to this phenomenon have been numerically studied for the specific case of a multistage pump assembly consisting of a series of channels with linearly diverging, converging or uniform rectangular cross sections. Various combinations of these three geometrical configurations have been analyzed and key parameters of the pump, such as net mass flow rate and final pressure difference, have been compared. Modeling is based on the linearized Shakhov model kinetic equation with diffuse boundary conditions while the channels are modeled adequately long in order to justify the implemented infinite capillary methodology. In all configurations under investigation the characteristic curves of the net mass flow rate versus the pressure difference in terms of channel geometry, input pressure, imposed temperature ratio and number of stages have been obtained. By calculating the characteristic curves of the pump as a function of the geometry, operating conditions and number of stages, the present work provides a powerful modeling tool for the pre-sizing of a multistage Knudsen pump prototype meeting given pumping specifications. The next part of this work, which is under way, is the design of an experimental setup in order to confirm modeling results and to identify problems and constraints related to manufacturing and temperature control on the device.
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A novel configuration of Knudsen pump is numerically studied in this paper. The pumping element consists of two facing isothermal ratchet surfaces at different temperatures. Since the main practical difficulty associated with traditional... more
A novel configuration of Knudsen pump is numerically studied in this paper. The pumping element consists of two facing isothermal ratchet surfaces at different temperatures. Since the main practical difficulty associated with traditional Knudsen pumps which refers to the necessity to accurately control the temperature gradient imposed along the walls of the device, the possibility of independently heating or cooling two distinct surfaces can be considered as a turnaround point in the design simplification of such new generation pumps. The micrometric dimensions of the pump provide the necessary conditions for obtaining rarefied gas inside the device and the asymmetric saw-tooth-like surfaces provide the optimal geometrical conditions in order to create temperature inequalities along the flow that finally engender a macroscopic gas movement. The rarefied flow is numerically investigated by Direct Simulation Monte Carlo (DSMC) in a large range of Knudsen number. The mass flowrate reac...
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A series of new bi-stable fluidic oscillators which can generate discrete pulsed jets in a wide frequency range (50-300Hz) with maximum velocities of the order of 200 m/s has been developed for flow separation control purposes. A... more
A series of new bi-stable fluidic oscillators which can generate discrete pulsed jets in a wide frequency range (50-300Hz) with maximum velocities of the order of 200 m/s has been developed for flow separation control purposes. A preliminary experimental analysis of the prototypes has been performed and the results have shown that the oscillation frequency has a nearly linear relationship with the length of its feedback loops. Thus, a new function is proposed to estimate the oscillation frequency according to the experimental results. In addition, numerical simulations are carried out in order to better understand the jet switching mechanism inside the oscillator and identify the parameters controlling the dynamics of these oscillations. Then, it is verified that the switching process of the internal jet is not only controlled by the pressure difference between the two control ports, but also by the pressure difference between the two main branches of the oscillator. Finally, two me...
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Over the past two decades a large number of MEMS and micro-devices have been developed. These miniaturized systems, such as lab-on-chip sensors, gas chromatography analyzers, etc., require micro-pumps for air sampling through the testing... more
Over the past two decades a large number of MEMS and micro-devices have been developed. These miniaturized systems, such as lab-on-chip sensors, gas chromatography analyzers, etc., require micro-pumps for air sampling through the testing stages of the device. Additionally, some microscale components such as radio frequency switches, microscopic vacuum tubes and other parts that depend on electron or ion optics, require certain vacuum environment for proper operation. Simply sealing the devices is not sufficient because leaks and outgassing are excessively detrimental in vacuum devices at microscale level. Accordingly, such components may need vacuum pumping to maintain proper functionality. The thermal transpiration phenomenon has been extensively investigated; however, functional prototypes based on this phenomenon have been only recently developed. The Knudsen pump, which is one of the devices exploiting this well-known phenomenon, is able to generate a macroscopic gas flow by sol...
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For years, the thermal transpiration phenomenon has been widely studied but regarding its real application to pumping, functional prototypes have been developed only in the recent years. The Knudsen pump exploits the well-known thermal... more
For years, the thermal transpiration phenomenon has been widely studied but regarding its real application to pumping, functional prototypes have been developed only in the recent years. The Knudsen pump exploits the well-known thermal transpiration phenomenon, and is able to generate a macroscopic flow of gas by solely applying a tangential temperature gradient along a wall without any initial pressure gradient. Since the Knudsen pump allows gas movement only when the gas is under rarefied conditions, specific geometrical configurations need to be investigated to optimize the functionality of the pump in terms of its detailed geometry taking into consideration the operating pressure level in the system [1]. Thus, analytical and numerical solutions have been provided for different cases [2] and experimental works for measuring the thermal transpiration in simple configurations have been achieved [3]. However, when it comes to the particular point of fabricating a real working Knudse...
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This work is part of a larger effort to miniaturize a microfluidic formaldehyde sensing device recently developed and commercialized by InAirSolutions Strasbourg 1. The detector is already an innovation in the field being capable to... more
This work is part of a larger effort to miniaturize a microfluidic formaldehyde sensing device recently developed and commercialized by InAirSolutions Strasbourg 1. The detector is already an innovation in the field being capable to detect continuously formaldehyde concentrations lower than 1 ppb in stabilized conditions and long range campaigns, fulfilling the new imposed regulations in the field of indoor air pollution [1]. The sensing device works in four steps: i) gas sampling, ii) trapping of formaldehyde from air to a liquid reagent, iii) derivatization reaction with acetylacetone solution at 65°C producing a fluorescent compound (DDL), iv) colorimetric detection employing a commercial fluorescence detection system. Apart of increasing significantly the overall price of the system, the commercial fluorescence systems has a large dead volume decreasing the response time of the measurement process and increasing the necessary liquid flow rate. Starting from this current situatio...
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Fluidic oscillators are no-moving-part actuators that can be used to produce pulsating jets. The characteristics of these devices and of the flow fields they produce are of particular interest in the field of heat transfer, as pulsating... more
Fluidic oscillators are no-moving-part actuators that can be used to produce pulsating jets. The characteristics of these devices and of the flow fields they produce are of particular interest in the field of heat transfer, as pulsating impinging jets have been shown to improve heat transfer compared to steady jets. In this study, special focus is given to these characteristics as a preparation for a subsequent thermal study that will evaluate the performance of these pulsed jets against steady jets. The functioning of the device in response to different operating and design parameters is first considered. It was shown that a transition between different operating modes is possible, depending on both the inlet mass flowrate and the width of the feedback channel of the device. This was followed by a study of the velocity fields of the pulsed jets produced by the device. More specifically, attention is given to the developing characteristics and flow structures of the pulsating free j...
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Thermometry techniques have been widely developed during the last decades to analyze thermal properties of various fluid flows. Following the increasing interest for microfluidic applications, most of these techniques have been adapted to... more
Thermometry techniques have been widely developed during the last decades to analyze thermal properties of various fluid flows. Following the increasing interest for microfluidic applications, most of these techniques have been adapted to the microscale and some new experimental approaches have emerged. In the last years, the need for a detailed experimental analysis of gaseous microflows has drastically grown due to a variety of exciting new applications. Unfortunately, thermometry is not yet well developed for analyzing gas flows at the microscale. Thus, the present review aims at analyzing the main currently available thermometry techniques adapted to microflows. Following a rapid presentation and classification of these techniques, the review is focused on optical techniques, which are the most suited for application at microscale. Their presentation is followed by a discussion about their applicability to gas microflows, especially in confined conditions, and the current challe...
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Formaldehyde (HCHO), a chemical compound used in the fabrication process of a broad range of household products, is present indoors as an airborne pollutant due to its high volatility caused by its low boiling point ( T = − 19 °C).... more
Formaldehyde (HCHO), a chemical compound used in the fabrication process of a broad range of household products, is present indoors as an airborne pollutant due to its high volatility caused by its low boiling point ( T = − 19 °C). Miniaturization of analytical systems towards palm-held devices has the potential to provide more efficient and more sensitive tools for real-time monitoring of this hazardous air pollutant. This work presents the initial steps and results of the prototyping process towards on-chip integration of HCHO sensing, based on the Hantzsch reaction coupled to the fluorescence optical sensing methodology. This challenge was divided into two individually addressed problems: (1) efficient airborne HCHO trapping into a microfluidic context and (2) 3,5–diacetyl-1,4-dihydrolutidine (DDL) molecular sensing in low interrogation volumes. Part (2) was addressed in this paper by proposing, fabricating, and testing a fluorescence detection system based on an ultra-low light ...
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Miniaturization of continuous fluorescence detection is a challenging task due to the multiple and sensitive parameters intervening in the process. By analyzing fluorescence sensing architectures proposed during the last two years, this... more
Miniaturization of continuous fluorescence detection is a challenging task due to the multiple and sensitive parameters intervening in the process. By analyzing fluorescence sensing architectures proposed during the last two years, this work has the goal to identify some trends in the process of fluorescence miniaturization for in-time liquid detection. A lack of postulated strategies regarding the miniaturization process was observed and this review tries to answer partially to this need. The identified integration strategies excel in fulfilling partially the desired functions of a fully autonomous miniaturized detector and further research is needed in order to develop sensing micro-system being capable to step outside of the lab world.
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Gas behavior in systems at microscale has been receiving significant attention from researchers in the last two decades [1-4]. Today, there is an enhanced emphasis on developing new experimental techniques to capture the local temperature... more
Gas behavior in systems at microscale has been receiving significant attention from researchers in the last two decades [1-4]. Today, there is an enhanced emphasis on developing new experimental techniques to capture the local temperature profiles in gases at rarefied conditions. The main underlying reason behind this focus is the interesting physics exhibited by gases at these rarefied conditions, especially in the transition regime. There is the onset of local thermodynamic disequilibrium, which manifests as velocity slip and temperature jump [1-4] at the wall. However, there is limited experimental evidence on understanding these aforementioned phenomena. With the advances in experimental facilities, it is today possible, at least in principle, to map the local temperature profiles in gases at rarefied conditions. Molecular tagging approach is one such technique which has shown the potential to map the temperature profile in low pressure conditions [5]. In molecular tagging appro...
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In this work, a compact gas chromatograph prototype for near real-time benzene, toluene, ethylbenzene and xylenes (BTEX) detection at sub-ppb levels has been developed. The system is composed of an aluminium preconcentrator (PC) filled... more
In this work, a compact gas chromatograph prototype for near real-time benzene, toluene, ethylbenzene and xylenes (BTEX) detection at sub-ppb levels has been developed. The system is composed of an aluminium preconcentrator (PC) filled with Basolite C300, a 20 m long Rxi-624 capillary column and a photoionization detector. The performance of the device has been evaluated in terms of adsorption capacity, linearity and sensitivity. Initially, PC breakthrough time for an equimolar 1 ppm BTEX mixture has been determined showing a remarkable capacity of the adsorbent to quantitatively trap BTEX even at high concentrations. Then, a highly linear relationship between sample volume and peak area has been obtained for all compounds by injecting 100-ppb samples with volumes ranging from 5–80 mL. Linear plots were also observed when calibration was conducted in the range 0–100 ppb using a 20 mL sampling volume implying a total analysis time of 19 min. Corresponding detection limits of 0.20, 0....