This paper presents a numerical analysis of the behavior of synthetic jets with submillimetric (m... more This paper presents a numerical analysis of the behavior of synthetic jets with submillimetric (mini jet) and micrometric (micro jet) dimensions, conducted with the CFD code Fluent. The mini jet is also experimentally studied being operated by a pneumatic signal generator and the velocities measured by hot-wire anemometry techniques. The experiments allow to discuss and to validate the numerical simulation for the mini jet which leads to conclusions relative to the micro jet real performances. L'article présente une analyse numérique du comportement de jets synthétiques ayant des dimensions millimétriques (mini jet) ou submillimétriques (micro jet). Le mini-jet étudié aussi expérimentalement est produit par un système pneumatique et les vitesses sont mesurées par anémométrie à fil chaud. Les expériences permettent de discuter et de valider la simulation numérique pour le mini-jet qui conduit aux conclusions sur les performances du micro-jet.
This chapter examines various measurement techniques adaptable to the experimental study of the b... more This chapter examines various measurement techniques adaptable to the experimental study of the behavior of fluidic microsystems. It only considers measurements in single-phase flows. Some of the characteristic quantities such as pressure, temperature, flow rate or velocity, are often of the same order in microflows as with classic macroflows. However, their determination at the microscale, particularly when local measurements are needed, is strongly dependant on the geometric configuration of the microsystem. On the contrary, typical flow rates in microsystems are often very low and their measurement requires specific techniques. Fluidic connections can add non-negligible fluid volumes that have to be taken into account in measurement analysis, particularly for unsteady flow studies, to the system studied. Thus, for each characteristic quantity, steady flow measurements and - when possible - unsteady flow measurements are both presented in the chapter.Controlled Vocabulary Termsflu...
The active flow control is a research field in broad expansion. Its main objective is the improve... more The active flow control is a research field in broad expansion. Its main objective is the improvement of vehicles aerodynamics by controlling the flow in the boundary layer. The control is made by modifying the flow in the boundary layer by means of actuators. This control may increase the lift, decrease the drag and improve the stability of the vehicle. This study is focused on a microfluidic oscillator used as an actuator for flow separation control. It consists, essentially, in a nozzle, two exits of sub-millimetric dimensions and two feedback loops. We present here the design and fabrication of a bi-stable fluidic oscillator. To develop and design this oscillator, CFD calculations have been used. The obtained prototype has been characterized experimentally in a quiescent environment by using a hot wire. The interaction of the produced microjets with a transversal flow has also been analyzed using the particle image velocimetry (PIV) technique.
ABSTRACT Fluidic microdiodes are devices with no mobile parts, which can be used to replace check... more ABSTRACT Fluidic microdiodes are devices with no mobile parts, which can be used to replace check valves in micropumps in order to increase their reliability. In this paper, the influence of the divergence angle on the efficiency of convergent/divergent diodes with constant depth is studied. Our numerical model built up with the CFD code Fluent is first validated thanks to experimental results available in the literature. The numerical study shows then that the preferential direction of the flow in the diode is dependant both on the divergence angle and on the pressure drop imposed through the device. The same parametrical study is done on convergent/divergent pyramid-shaped diodes. Behaviour differences are outlined and conclusions about the optimisation of such microdiodes used in micropumps are deducted from these results.
Analysis of gas and liquid flows in micro-ducts: delinking of the experimental uncertainties » Th... more Analysis of gas and liquid flows in micro-ducts: delinking of the experimental uncertainties » The different sources of uncertainty that occur during the experimental study of steady flows through micro-ducts is analyzed. It is noticed that the lack of precision when measuring the geometrical dimensions of the sections plays a crucial role. A method is proposed to avoid this source
Volume 6: Fluids and Thermal Systems; Advances for Process Industries, Parts A and B, 2011
ABSTRACT A new setup was developed for gas mixing analysis in T-shaped microchannels. The princip... more ABSTRACT A new setup was developed for gas mixing analysis in T-shaped microchannels. The principle of the flow rate measurement was based on the Constant Volume (CV) method [1]. The mass flow rate measurements of two gases N2 / CO2 mixing in a T mixer were carried out in the slip flow regime and followed by a simulation work for comparison. The mass flow rate has a magnitude of 10−8 or 10−7 kg/s and has good agreement with simulation for the lowest inlet over outlet pressures ratios and moderate agreement for the highest inlet over outlet pressures ratios.
This paper presents a numerical analysis of the behavior of synthetic jets with submillimetric (m... more This paper presents a numerical analysis of the behavior of synthetic jets with submillimetric (mini jet) and micrometric (micro jet) dimensions, conducted with the CFD code Fluent. The mini jet is also experimentally studied being operated by a pneumatic signal generator and the velocities measured by hot-wire anemometry techniques. The experiments allow to discuss and to validate the numerical simulation for the mini jet which leads to conclusions relative to the micro jet real performances. L'article présente une analyse numérique du comportement de jets synthétiques ayant des dimensions millimétriques (mini jet) ou submillimétriques (micro jet). Le mini-jet étudié aussi expérimentalement est produit par un système pneumatique et les vitesses sont mesurées par anémométrie à fil chaud. Les expériences permettent de discuter et de valider la simulation numérique pour le mini-jet qui conduit aux conclusions sur les performances du micro-jet.
The active flow control is a research field in broad expansion. Its main objective is the improve... more The active flow control is a research field in broad expansion. Its main objective is the improvement of vehicles aerodynamics by controlling the flow in the boundary layer. The control is made by modifying the flow in the boundary layer by means of actuators. This control may increase the lift, decrease the drag and improve the stability of the vehicle. This study is focused on a microfluidic oscillator used as an actuator for flow separation control. It consists, essentially, in a nozzle, two exits of sub-millimetric dimensions and two feedback loops. We present here the design and fabrication of a bi-stable fluidic oscillator. To develop and design this oscillator, CFD calculations have been used. The obtained prototype has been characterized experimentally in a quiescent environment by using a hot wire. The interaction of the produced microjets with a transversal flow has also been analyzed using the particle image velocimetry (PIV) technique.
Comptes Rendus de l'Académie des Sciences - Series IIB - Mechanics-Physics-Chemistry-Astronomy, 1997
ABSTRACT Les systèmes de préhension par le vide utilisant un ensemble de ventouses ont de nombreu... more ABSTRACT Les systèmes de préhension par le vide utilisant un ensemble de ventouses ont de nombreux avantages. Cependant un problème important apparaît lorsque certaines d'entre elles n'ont pas de pièce en vis-à-vis. En effet, le débit inutilement aspiré induit une forte consommation énergétique et le taux de vide peut devenir insuffisant. Il est donc nécessaire de désactiver toutes les ventouses inutilisées pour la préhension. Nous proposons dans cette note la présentation d'une solution originale, utilisant le débit aspiré pour détecter et actionner l'obturation des ventouses non utilisées.AbstractVacuum prehensile systems using a set of suction cups offer many advantages. However, an important problem appears when there is no matter in front of some suction cups. Indeed the flow rate sucked up in vain induces a considerable waste of energy and the vacuum level may become insufficient for gripping. Therefore it is very useful to disconnect all the suction cups that are not being used for gripping. In this paper, we present a new solution using the sucked up flow rate to detect and to drive the closing of unused suction cups.
ABSTRACT Many experimental works which appeared in the last decade in the open literature conclud... more ABSTRACT Many experimental works which appeared in the last decade in the open literature concluded that for channel having a hydraulic diameter less than 1 mm the conventional theory can no longer be considered as able to predict the pressure drop and convective heat transfer coefficients. From a chronological analysis of these experimental results, it is possible to remark that the observed deviations from the prediction of the conventional theory are decreasing. This fact can be explained by considering the dramatic improvement in the microfabrication techniques with the consequent more appropriate control of the channels' cross-section and the increase in the reliability/accuracy of the recent experimental data. In this paper the conventional theory is used to calculate numerically the Poiseuille numbers and the Nusselt numbers for trapezoidal and rectangular microchannels in which a liquid flows in laminar regime. It is evidenced the role of the cross-section geometry on the pressure drops and the local values of the convective heat transfer coefficients by taking into account the viscous dissipation inside the fluid. The numerical results presented in this paper have evidenced that the conventional theory is able to explain the experimental results obtained for trapezoidal microchannels in terms of friction factors for microchannels with hydraulic diameters greater than 30 μm. It has been demonstrated that for liquid flows, if the microchannel hydraulic diameter becomes less than 50 μm, viscous dissipation effects cannot be ignored for large Reynolds numbers.
ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels, 2012
ABSTRACT The Molecular Tagging Velocimetry (MTV) technique has been widely used for analyzing vel... more ABSTRACT The Molecular Tagging Velocimetry (MTV) technique has been widely used for analyzing velocity fields in liquid mini- and microflows. Concerning gaseous flows, only few works describe the implementation of MTV at millimetric scale, and these studies are limited to the analysis of external flows, such as jet flows. The goal of the present work is to develop this technique for the analysis of internal gas flows in minichannels. It is a first step toward the visualization of velocity profiles in rarefied conditions, and direct measurement of velocity slip at the walls.A specific experimental setup has been designed. Its features are detailed. Velocity profiles are obtained in a pressure driven steady flow of argon through a long rectangular minichannel of 1.2 × 5 mm2 cross-section and 15 cm length using acetone molecules as tracer. Experiments are carried out at atmospheric pressure, in a laminar continuum flow regime. The accuracy of the method is discussed by comparison between experimental and theoretical velocity profiles.The potential of the MTV technique for analyzing mini or micro gaseous internal flows is commented on. Perspectives of the work for discussing the validity of boundary conditions in the slip flow regime are presented.
This paper presents a numerical analysis of the behavior of synthetic jets with submillimetric (m... more This paper presents a numerical analysis of the behavior of synthetic jets with submillimetric (mini jet) and micrometric (micro jet) dimensions, conducted with the CFD code Fluent. The mini jet is also experimentally studied being operated by a pneumatic signal generator and the velocities measured by hot-wire anemometry techniques. The experiments allow to discuss and to validate the numerical simulation for the mini jet which leads to conclusions relative to the micro jet real performances. L'article présente une analyse numérique du comportement de jets synthétiques ayant des dimensions millimétriques (mini jet) ou submillimétriques (micro jet). Le mini-jet étudié aussi expérimentalement est produit par un système pneumatique et les vitesses sont mesurées par anémométrie à fil chaud. Les expériences permettent de discuter et de valider la simulation numérique pour le mini-jet qui conduit aux conclusions sur les performances du micro-jet.
This chapter examines various measurement techniques adaptable to the experimental study of the b... more This chapter examines various measurement techniques adaptable to the experimental study of the behavior of fluidic microsystems. It only considers measurements in single-phase flows. Some of the characteristic quantities such as pressure, temperature, flow rate or velocity, are often of the same order in microflows as with classic macroflows. However, their determination at the microscale, particularly when local measurements are needed, is strongly dependant on the geometric configuration of the microsystem. On the contrary, typical flow rates in microsystems are often very low and their measurement requires specific techniques. Fluidic connections can add non-negligible fluid volumes that have to be taken into account in measurement analysis, particularly for unsteady flow studies, to the system studied. Thus, for each characteristic quantity, steady flow measurements and - when possible - unsteady flow measurements are both presented in the chapter.Controlled Vocabulary Termsflu...
The active flow control is a research field in broad expansion. Its main objective is the improve... more The active flow control is a research field in broad expansion. Its main objective is the improvement of vehicles aerodynamics by controlling the flow in the boundary layer. The control is made by modifying the flow in the boundary layer by means of actuators. This control may increase the lift, decrease the drag and improve the stability of the vehicle. This study is focused on a microfluidic oscillator used as an actuator for flow separation control. It consists, essentially, in a nozzle, two exits of sub-millimetric dimensions and two feedback loops. We present here the design and fabrication of a bi-stable fluidic oscillator. To develop and design this oscillator, CFD calculations have been used. The obtained prototype has been characterized experimentally in a quiescent environment by using a hot wire. The interaction of the produced microjets with a transversal flow has also been analyzed using the particle image velocimetry (PIV) technique.
ABSTRACT Fluidic microdiodes are devices with no mobile parts, which can be used to replace check... more ABSTRACT Fluidic microdiodes are devices with no mobile parts, which can be used to replace check valves in micropumps in order to increase their reliability. In this paper, the influence of the divergence angle on the efficiency of convergent/divergent diodes with constant depth is studied. Our numerical model built up with the CFD code Fluent is first validated thanks to experimental results available in the literature. The numerical study shows then that the preferential direction of the flow in the diode is dependant both on the divergence angle and on the pressure drop imposed through the device. The same parametrical study is done on convergent/divergent pyramid-shaped diodes. Behaviour differences are outlined and conclusions about the optimisation of such microdiodes used in micropumps are deducted from these results.
Analysis of gas and liquid flows in micro-ducts: delinking of the experimental uncertainties » Th... more Analysis of gas and liquid flows in micro-ducts: delinking of the experimental uncertainties » The different sources of uncertainty that occur during the experimental study of steady flows through micro-ducts is analyzed. It is noticed that the lack of precision when measuring the geometrical dimensions of the sections plays a crucial role. A method is proposed to avoid this source
Volume 6: Fluids and Thermal Systems; Advances for Process Industries, Parts A and B, 2011
ABSTRACT A new setup was developed for gas mixing analysis in T-shaped microchannels. The princip... more ABSTRACT A new setup was developed for gas mixing analysis in T-shaped microchannels. The principle of the flow rate measurement was based on the Constant Volume (CV) method [1]. The mass flow rate measurements of two gases N2 / CO2 mixing in a T mixer were carried out in the slip flow regime and followed by a simulation work for comparison. The mass flow rate has a magnitude of 10−8 or 10−7 kg/s and has good agreement with simulation for the lowest inlet over outlet pressures ratios and moderate agreement for the highest inlet over outlet pressures ratios.
This paper presents a numerical analysis of the behavior of synthetic jets with submillimetric (m... more This paper presents a numerical analysis of the behavior of synthetic jets with submillimetric (mini jet) and micrometric (micro jet) dimensions, conducted with the CFD code Fluent. The mini jet is also experimentally studied being operated by a pneumatic signal generator and the velocities measured by hot-wire anemometry techniques. The experiments allow to discuss and to validate the numerical simulation for the mini jet which leads to conclusions relative to the micro jet real performances. L'article présente une analyse numérique du comportement de jets synthétiques ayant des dimensions millimétriques (mini jet) ou submillimétriques (micro jet). Le mini-jet étudié aussi expérimentalement est produit par un système pneumatique et les vitesses sont mesurées par anémométrie à fil chaud. Les expériences permettent de discuter et de valider la simulation numérique pour le mini-jet qui conduit aux conclusions sur les performances du micro-jet.
The active flow control is a research field in broad expansion. Its main objective is the improve... more The active flow control is a research field in broad expansion. Its main objective is the improvement of vehicles aerodynamics by controlling the flow in the boundary layer. The control is made by modifying the flow in the boundary layer by means of actuators. This control may increase the lift, decrease the drag and improve the stability of the vehicle. This study is focused on a microfluidic oscillator used as an actuator for flow separation control. It consists, essentially, in a nozzle, two exits of sub-millimetric dimensions and two feedback loops. We present here the design and fabrication of a bi-stable fluidic oscillator. To develop and design this oscillator, CFD calculations have been used. The obtained prototype has been characterized experimentally in a quiescent environment by using a hot wire. The interaction of the produced microjets with a transversal flow has also been analyzed using the particle image velocimetry (PIV) technique.
Comptes Rendus de l'Académie des Sciences - Series IIB - Mechanics-Physics-Chemistry-Astronomy, 1997
ABSTRACT Les systèmes de préhension par le vide utilisant un ensemble de ventouses ont de nombreu... more ABSTRACT Les systèmes de préhension par le vide utilisant un ensemble de ventouses ont de nombreux avantages. Cependant un problème important apparaît lorsque certaines d'entre elles n'ont pas de pièce en vis-à-vis. En effet, le débit inutilement aspiré induit une forte consommation énergétique et le taux de vide peut devenir insuffisant. Il est donc nécessaire de désactiver toutes les ventouses inutilisées pour la préhension. Nous proposons dans cette note la présentation d'une solution originale, utilisant le débit aspiré pour détecter et actionner l'obturation des ventouses non utilisées.AbstractVacuum prehensile systems using a set of suction cups offer many advantages. However, an important problem appears when there is no matter in front of some suction cups. Indeed the flow rate sucked up in vain induces a considerable waste of energy and the vacuum level may become insufficient for gripping. Therefore it is very useful to disconnect all the suction cups that are not being used for gripping. In this paper, we present a new solution using the sucked up flow rate to detect and to drive the closing of unused suction cups.
ABSTRACT Many experimental works which appeared in the last decade in the open literature conclud... more ABSTRACT Many experimental works which appeared in the last decade in the open literature concluded that for channel having a hydraulic diameter less than 1 mm the conventional theory can no longer be considered as able to predict the pressure drop and convective heat transfer coefficients. From a chronological analysis of these experimental results, it is possible to remark that the observed deviations from the prediction of the conventional theory are decreasing. This fact can be explained by considering the dramatic improvement in the microfabrication techniques with the consequent more appropriate control of the channels' cross-section and the increase in the reliability/accuracy of the recent experimental data. In this paper the conventional theory is used to calculate numerically the Poiseuille numbers and the Nusselt numbers for trapezoidal and rectangular microchannels in which a liquid flows in laminar regime. It is evidenced the role of the cross-section geometry on the pressure drops and the local values of the convective heat transfer coefficients by taking into account the viscous dissipation inside the fluid. The numerical results presented in this paper have evidenced that the conventional theory is able to explain the experimental results obtained for trapezoidal microchannels in terms of friction factors for microchannels with hydraulic diameters greater than 30 μm. It has been demonstrated that for liquid flows, if the microchannel hydraulic diameter becomes less than 50 μm, viscous dissipation effects cannot be ignored for large Reynolds numbers.
ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels, 2012
ABSTRACT The Molecular Tagging Velocimetry (MTV) technique has been widely used for analyzing vel... more ABSTRACT The Molecular Tagging Velocimetry (MTV) technique has been widely used for analyzing velocity fields in liquid mini- and microflows. Concerning gaseous flows, only few works describe the implementation of MTV at millimetric scale, and these studies are limited to the analysis of external flows, such as jet flows. The goal of the present work is to develop this technique for the analysis of internal gas flows in minichannels. It is a first step toward the visualization of velocity profiles in rarefied conditions, and direct measurement of velocity slip at the walls.A specific experimental setup has been designed. Its features are detailed. Velocity profiles are obtained in a pressure driven steady flow of argon through a long rectangular minichannel of 1.2 × 5 mm2 cross-section and 15 cm length using acetone molecules as tracer. Experiments are carried out at atmospheric pressure, in a laminar continuum flow regime. The accuracy of the method is discussed by comparison between experimental and theoretical velocity profiles.The potential of the MTV technique for analyzing mini or micro gaseous internal flows is commented on. Perspectives of the work for discussing the validity of boundary conditions in the slip flow regime are presented.
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Papers by Lucien Baldas