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Harald Pasch - One of the best experts on this subject based on the ideXlab platform.

  • comprehensive High Temperature two dimensional liquid chromatography combined with High Temperature Gradient chromatography infrared spectroscopy for the analysis of impact polypropylene copolymers
    Journal of Chromatography A, 2013
    Co-Authors: Sadiqali Cheruthazhekatt, Gareth W Harding, Harald Pasch
    Abstract:

    Abstract Impact polypropylene copolymers (IPC) are extremely complex materials that can only be effectively analysed by multidimensional analytical approaches. IPC consists of isotactic polypropylene (iPP) as the major phase, ethylene–propylene (EP) copolymers of various compositions and small amounts of polyethylene. The molecular heterogeneity of two IPC samples having different ethylene contents was studied by using a novel cross-fractionation technique, developed from a combination of various analytical separation methods into an effective characterisation tool for complex polyolefins. The initial step involves the fractionation of the sample into EP rubber, EP segmented copolymer, and iPP, by preparative Temperature rising elution fractionation (TREF). The resulting fractions are still distributed with regards to chemical composition and molar mass. The separation with respect to these parameters is conducted by comprehensive HT 2D-LC. This is the first time that the individual components in all TREF fractions of an IPC are separated and analysed mutidimensionally, by both SEC-FTIR, High-Temperature (HT) HPLC-FTIR, and HT 2D-LC. Molar mass analysis of the chemically homogeneous fractions from HT HPLC is accomplished by HT SEC in the second dimension of HT 2D-LC. The chemical composition of all species is determined by coupling FTIR spectroscopy to HT HPLC via an LC-transform interface. This novel approach reveals the capability of this hyphenated technique to determine the exact chemical composition of the individual components in the complex TREF fractions of IPCs. The HT HPLC-FTIR results confirm the separation mechanism in the given chromatographic system using a 1-decanol to TCB solvent Gradient and a Hypercarb stationary phase. The components of differing chemical composition are separated according to the nature and length of the propylene/ethylene segments, with their arrangement in the chains strongly affecting their adsorption/desorption on the stationary phase. FTIR analysis provides information on the ethylene and propylene contents of the fractions as well as on the ethylene and propylene crystallinities.

  • High-Temperature Gradient HPLC and LC-NMR for the analysis of complex polyolefins
    Pure and Applied Chemistry, 2008
    Co-Authors: Harald Pasch, Lars-christian Heinz, Tibor Macko, Wolf Hiller
    Abstract:

    The synthesis and characterization of polyolefins continues to be one of the most important areas for academic and industrial polymer research. One consequence of the de- velopment of new "tailor-made" polyolefins is the need for new and improved analytical techniques for the analysis of polyolefins with respect to molar mass and chemical composi- tion distribution. The present article briefly reviews different new and relevant techniques for polyolefin analysis. Crystallization analysis fractionation is a powerful new technique for the analysis of short-chain branching in linear low-density polyethylene (LLDPE) and the analy- sis of polyolefin blends and copolymers regarding chemical composition. For the fast analy- sis of the chemical composition distribution, a new High-Temperature Gradient High-perform- ance liquid chromatography (HPLC) system has been developed. The efficiency of this system for the separation of various olefin copolymers is demonstrated. The correlation be- tween molar mass and chemical composition can be accessed by on-line coupling of High- Temperature size exclusion chromatography (HT-SEC) and 1 H NMR spectroscopy. It is shown that the on-line NMR analysis of chromatographic fractions yields information on microstructure and tacticity in addition to molar mass and copolymer composition.

  • separation and characterization of ethylene propylene copolymers by High Temperature Gradient hplc coupled to ftir spectroscopy
    Macromolecular Symposia, 2007
    Co-Authors: Andreas Albrecht, Lars-christian Heinz, Dieter Lilge, Harald Pasch
    Abstract:

    The chromatographic separation of ethylene-propylene (EP) copolymers with regard to chemical composition was accomplished by a new technique - High-Temperature Gradient HPLC. Using a mobile phase of ethylene glycol monobutylether (EGMBE) and 1,2,4-trichlorobenzene (TCB), and silica gel as the stationary phase, copolymers with different ethylene contents were separated according to their chemical compositions. Using a sample solvent of n-decanol and a column Temperature of140°C, chromatographic conditions were established that correspond to separation in a precipitation-redissolution mechanism. With the aim to obtain further information on the separation process, the HPLC system was coupled to FTIR spectroscopy through a LC-Transform interface. The FTIR data confirmed that the copolymers were separated according to the ethylene content of the eluted samples.

  • separation of ethylene vinyl acetate copolymers by High Temperature Gradient liquid chromatography
    Macromolecules, 2007
    Co-Authors: Andreas Albrecht, Robert Brüll, And Tibor Macko, Harald Pasch
    Abstract:

    Ethylene−vinyl acetate (EVA) copolymers can be semicrystalline or amorphous materials, depending on their chemical composition. A variety of different methods were used for the analysis of the chemical composition distribution of these copolymers, which in general were time- and labor-consuming and could be applied only for a limited range of compositions. In the present work a novel chromatographic method is presented that can be used for chemical composition analysis regardless of the composition of the copolymer. High-Temperature Gradient HPLC has been found to be suitable for chemical composition separation of semicrystalline and amorphous EVA copolymers. In addition, separation is achieved from the respective homopolymers. We have found that Gradients of 1,2,4-trichlorobenzene/cyclohexanone, decalin/cyclohexanone, and decalin/1-decanol enable the selective elution of the copolymers from silica gel at 140 °C. The EVA copolymers elute in dependence of their content of the polar vinyl acetate comonomer....

  • Separation of Ethylene−Vinyl Acetate Copolymers by High-Temperature Gradient Liquid Chromatography
    Macromolecules, 2007
    Co-Authors: Andreas Albrecht, Robert Brüll, And Tibor Macko, Harald Pasch
    Abstract:

    Ethylene−vinyl acetate (EVA) copolymers can be semicrystalline or amorphous materials, depending on their chemical composition. A variety of different methods were used for the analysis of the chemical composition distribution of these copolymers, which in general were time- and labor-consuming and could be applied only for a limited range of compositions. In the present work a novel chromatographic method is presented that can be used for chemical composition analysis regardless of the composition of the copolymer. High-Temperature Gradient HPLC has been found to be suitable for chemical composition separation of semicrystalline and amorphous EVA copolymers. In addition, separation is achieved from the respective homopolymers. We have found that Gradients of 1,2,4-trichlorobenzene/cyclohexanone, decalin/cyclohexanone, and decalin/1-decanol enable the selective elution of the copolymers from silica gel at 140 °C. The EVA copolymers elute in dependence of their content of the polar vinyl acetate comonomer....

Philippe Pernod - One of the best experts on this subject based on the ideXlab platform.

  • High Temperature Gradient micro-sensors array for flow separation detection and control
    Smart Materials and Structures, 2019
    Co-Authors: Cécile Ghouila-houri, Abdelkrim Talbi, Romain Viard, Quentin Gallas, Eric Garnier, Alain Merlen, Philippe Pernod
    Abstract:

    This paper reports the use of an array of calorimetric micro-sensors that perform bidirectional measurement of wall shear stress, for flow separation detection and control. The sensors design is hot-wire like with three parallel micro wires suspended over a micro-cavity and mechanically supported using periodic perpendicular micro-bridges. The micro-sensors were implemented on a flexible packaging and characterized in a turbulent boundary layer wind tunnel on a flat plate. An array of twelve micro-sensors were then implemented in a flap model designed for active flow control experiments and equipped with pulsed jet actuators. The work included the design and manufacturing of appropriate miniaturized electronics. Without control, the micro-sensors successfully detected the natural flow separation and the flow separation point moving from the trailing edge to the leading edge as the angle of the flap increased. Finally, the micro-sensors characterized the efficiency of the active flow control for avoiding separation.

  • MEMS calorimetric transducers for flow separation detection and control
    2019
    Co-Authors: Cécile Ghouila-houri, Romain Viard, Quentin Gallas, Eric Garnier, Alain Merlen, Talbi Abdelkrim, Philippe Pernod
    Abstract:

    Robust micro machined High Temperature Gradient calorimetric (HTGC) transducers were developed for flow separation control. Based on thermal principle, the transducers measure the mean and fluctuating bidirectional shear stress that is particularly useful for flow separation detection. More than a hundred micro-sensors were simultaneously micro-machined using MEMS technology. A flexible array of calorimetric micro-sensors was implemented with miniaturized electronics on a flap model also equipped with pulsed jet actuators. Flow control experiments were successfully conducted as the natural separation occurring on the model was detected the HTGC micro sensors and controlled by pulsed jet actuation.

  • MEMS High Temperature Gradient sensor for skin-friction measurements in Highly turbulent flows
    2019 IEEE SENSORS, 2019
    Co-Authors: Cécile Ghouila-houri, Abdelkrim Talbi, Romain Viard, Quentin Gallas, Eric Garnier, Pascal Molton, Jérôme Delva, Alain Merlen, Philippe Pernod
    Abstract:

    This paper presents and discusses the results obtained with a MEMS High Temperature Gradient sensor for time-averaged and fluctuating skin-friction measurements in Highly turbulent flows. Designed as a robust wall-mounted suspended hot-wire structure, the micro-sensor showed a High Temperature variation for low power consumption. Successfully implemented into two air wind tunnels, the sensor was tested for velocities going up to 270 m/s, mean velocity of airliner cruise flights, and corresponding to a shear stress of 150 Pa. The microsensor thereby demonstrated its value for measuring turbulence in aerodynamic applications, particularly in aeronautics.

  • High Temperature Gradient nanogap-Pirani micro-sensor with maximum sensitivity around atmospheric pressure
    Applied Physics Letters, 2017
    Co-Authors: Cécile Ghouila-houri, Abdelkrim Talbi, Romain Viard, Quentin Gallas, Eric Garnier, Alain Merlen, Mohammed Moutaouekkil, Omar Elmazria, Philippe Pernod
    Abstract:

    This letter describes and discusses the design and testing of an effcient nanogap Pirani micro-sensor for pressure measurements in a wide range with a maximum sensitivity around atmospheric pressure. The structure combines a substrate-free heated wire and mechanical support using silicon oxide micro-bridges allowing both a constant nanoscale gap between the wire and the substrate and a 1 mm long and 3 µm wide wire. The High aspect ratio of wire provides a uniform heating profile along the wire and contributes to low pressure detection. At the opposite, both the nanoscale gap and the short wire length between two micro-bridges contributes to shift the High pressure limit. Tested between 10 kPa and 800 kPa, the sensor presents a wide measurement range, not fully reached by the experiments, with a maximum of sensitivity close to the atmospheric pressure and performances with up to 38 %/dec sensitivity when operation in constant Temperature mode with an overheat of 20 °C.

  • High Temperature Gradient calorimetric wall shear stress micro-sensor for flow separation detection
    Sensors and Actuators A: Physical, 2017
    Co-Authors: Cécile Ghouila-houri, Abdelkrim Talbi, Romain Viard, Quentin Gallas, Eric Garnier, Alain Merlen, Philippe Pernod
    Abstract:

    The paper describes and discusses the design and testing of an efficient and High-sensitivity calorimetricthermal sensor developed for bi-directional wall shear stress measurements in aerodynamic flows. Themain technical application targeted is flow separation detection. The measurement principle is basedon the forced convective heat transfer from a heater element. The sensor structure is composed of threeparallel substrate-free wires presenting a High aspect ratio and supported by periodic perpendicular SiO2micro-bridges. This hybrid structure takes advantages from both conventional hot-films and hot-wires,ensuring near-wall and non-intrusive measurement, mechanical toughness and thermal insulation tothe bulk substrate, and it allowed to add the calorimetric sensor functionality to detect simultaneouslythe wall shear stress amplitude and direction. The central wire is made of a multilayer structure com-posed of a heater element (Au/Ti) and a thermistor (Ni/Pt/Ni/Pt/Ni) enabling measurement of the heaterTemperature and a layer of SiO2 between them for electrical insulation. The upstream and downstreamwires are thermistors enabling operation in the calorimetric mode. This design provides a High tempera-ture Gradient and a homogeneous Temperature distribution along the wires. The sensor operates in bothconstant current and constant Temperature modes, with a feedback on current enabled by uncouplingheating and measurement. Welded on a flexible printed circuit, the sensor was flush mounted on the wallof a turbulent boundary layer wind tunnel. The experiments, conducted in both attached and separatedflow configurations, quantify the sensor response to a bi-directional wall shear stress up to 2.4 Pa anddemonstrate the sensor ability to detect flow separation.

Robert Brüll - One of the best experts on this subject based on the ideXlab platform.

  • characterization of ethylene propylene copolymers with High Temperature Gradient adsorption liquid chromatography and crystaf
    Journal of Applied Polymer Science, 2011
    Co-Authors: Tibor Macko, Robert Brüll, Yongmei Wang, Baudilio Coto, Inmaculada Suárez
    Abstract:

    Blends of linear polyethylene (PE) and isotactic polypropylene (iPP) with different average molar masses and a series of ethylene-propylene (EP) copolymers with different chemical composition as well as blends of PE, Ipp, and EP copolymers were separated using a carbon-column packing (Hypercarb®) and Gradients of 1-decanol or 2-ethyl-1-hexanol 1,2,4-trichlorobenzene (TCB). The separation is based on full adsorption of linear PE on the carbon sorbent at Temperature 160°C. However, iPP is not adsorbed and elutes in size exclusion mode. The random EP copolymers have been adsorbed in the column packing and separated according to their average chemical composition after application of the Gradient starting with alcohol and ending with pure TCB. The elution volumes of the copolymers depended linearly on the average concentration of ethylene in the copolymers. The HPLC elution profiles were correlated with the CRYSTAF elution profiles. In contrast to CRYSTAF, fully amorphous polyolefin samples were separated with the High-Temperature adsorption liquid chromatography. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

  • Characterization of ethylene‐propylene copolymers with High‐Temperature Gradient adsorption liquid chromatography and CRYSTAF
    Journal of Applied Polymer Science, 2011
    Co-Authors: Tibor Macko, Robert Brüll, Yongmei Wang, Baudilio Coto, Inmaculada Suárez
    Abstract:

    Blends of linear polyethylene (PE) and isotactic polypropylene (iPP) with different average molar masses and a series of ethylene-propylene (EP) copolymers with different chemical composition as well as blends of PE, Ipp, and EP copolymers were separated using a carbon-column packing (Hypercarb®) and Gradients of 1-decanol or 2-ethyl-1-hexanol 1,2,4-trichlorobenzene (TCB). The separation is based on full adsorption of linear PE on the carbon sorbent at Temperature 160°C. However, iPP is not adsorbed and elutes in size exclusion mode. The random EP copolymers have been adsorbed in the column packing and separated according to their average chemical composition after application of the Gradient starting with alcohol and ending with pure TCB. The elution volumes of the copolymers depended linearly on the average concentration of ethylene in the copolymers. The HPLC elution profiles were correlated with the CRYSTAF elution profiles. In contrast to CRYSTAF, fully amorphous polyolefin samples were separated with the High-Temperature adsorption liquid chromatography. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

  • Separation of short-chain branched polyolefins by High-Temperature Gradient adsorption liquid chromatography
    Analytical and bioanalytical chemistry, 2010
    Co-Authors: Tibor Macko, Robert Brüll, Rufina G. Alamo, Florian J. Stadler, Simone Losio
    Abstract:

    A new separation principle was recently introduced into the analytical characterization of polyolefins by researchers from the German Institute for Polymers in Darmstadt. It was demonstrated that polyolefins can be selectively separated via High-performance liquid chromatography on the basis of their adsorption/desorption behaviours at Temperatures as High as 160 °C. A Hypercarb® column packed with porous graphite gave the best results. The mobile phase consisted of a mixture of 1-decanol and 1,2,4-trichlorobenzene. In this work, the same chromatographic system is applied to the separation of ethylene/alkene and ethylene/norbornene copolymers. It was found that the elution volumes of the samples correlate linearly with the average chemical composition of samples. The elution volume is indirectly proportional to the concentration of branches in the ethylene/alkene copolymer. Branching shortens the length of continuous methylene sequences of the polymer backbone, thus decreasing the probability of orientation of a methylene sequence in a flat conformation on the graphite surface, which enables the most intensive van der Waals interactions between the methylene backbone and the carbon surface. An opposite trend in the elution order has been found for ethylene/norbornene copolymers. The elution volume of the ethylene/norbornene copolymers increased with the concentration of norbornene. It indicates pronounced attractive interactions between graphite and the cyclic comonomer.

  • separation of ethylene vinyl acetate copolymers by High Temperature Gradient liquid chromatography
    Macromolecules, 2007
    Co-Authors: Andreas Albrecht, Robert Brüll, And Tibor Macko, Harald Pasch
    Abstract:

    Ethylene−vinyl acetate (EVA) copolymers can be semicrystalline or amorphous materials, depending on their chemical composition. A variety of different methods were used for the analysis of the chemical composition distribution of these copolymers, which in general were time- and labor-consuming and could be applied only for a limited range of compositions. In the present work a novel chromatographic method is presented that can be used for chemical composition analysis regardless of the composition of the copolymer. High-Temperature Gradient HPLC has been found to be suitable for chemical composition separation of semicrystalline and amorphous EVA copolymers. In addition, separation is achieved from the respective homopolymers. We have found that Gradients of 1,2,4-trichlorobenzene/cyclohexanone, decalin/cyclohexanone, and decalin/1-decanol enable the selective elution of the copolymers from silica gel at 140 °C. The EVA copolymers elute in dependence of their content of the polar vinyl acetate comonomer....

  • Separation of Ethylene−Vinyl Acetate Copolymers by High-Temperature Gradient Liquid Chromatography
    Macromolecules, 2007
    Co-Authors: Andreas Albrecht, Robert Brüll, And Tibor Macko, Harald Pasch
    Abstract:

    Ethylene−vinyl acetate (EVA) copolymers can be semicrystalline or amorphous materials, depending on their chemical composition. A variety of different methods were used for the analysis of the chemical composition distribution of these copolymers, which in general were time- and labor-consuming and could be applied only for a limited range of compositions. In the present work a novel chromatographic method is presented that can be used for chemical composition analysis regardless of the composition of the copolymer. High-Temperature Gradient HPLC has been found to be suitable for chemical composition separation of semicrystalline and amorphous EVA copolymers. In addition, separation is achieved from the respective homopolymers. We have found that Gradients of 1,2,4-trichlorobenzene/cyclohexanone, decalin/cyclohexanone, and decalin/1-decanol enable the selective elution of the copolymers from silica gel at 140 °C. The EVA copolymers elute in dependence of their content of the polar vinyl acetate comonomer....

Andreas Albrecht - One of the best experts on this subject based on the ideXlab platform.

  • separation and characterization of ethylene propylene copolymers by High Temperature Gradient hplc coupled to ftir spectroscopy
    Macromolecular Symposia, 2007
    Co-Authors: Andreas Albrecht, Lars-christian Heinz, Dieter Lilge, Harald Pasch
    Abstract:

    The chromatographic separation of ethylene-propylene (EP) copolymers with regard to chemical composition was accomplished by a new technique - High-Temperature Gradient HPLC. Using a mobile phase of ethylene glycol monobutylether (EGMBE) and 1,2,4-trichlorobenzene (TCB), and silica gel as the stationary phase, copolymers with different ethylene contents were separated according to their chemical compositions. Using a sample solvent of n-decanol and a column Temperature of140°C, chromatographic conditions were established that correspond to separation in a precipitation-redissolution mechanism. With the aim to obtain further information on the separation process, the HPLC system was coupled to FTIR spectroscopy through a LC-Transform interface. The FTIR data confirmed that the copolymers were separated according to the ethylene content of the eluted samples.

  • separation of ethylene vinyl acetate copolymers by High Temperature Gradient liquid chromatography
    Macromolecules, 2007
    Co-Authors: Andreas Albrecht, Robert Brüll, And Tibor Macko, Harald Pasch
    Abstract:

    Ethylene−vinyl acetate (EVA) copolymers can be semicrystalline or amorphous materials, depending on their chemical composition. A variety of different methods were used for the analysis of the chemical composition distribution of these copolymers, which in general were time- and labor-consuming and could be applied only for a limited range of compositions. In the present work a novel chromatographic method is presented that can be used for chemical composition analysis regardless of the composition of the copolymer. High-Temperature Gradient HPLC has been found to be suitable for chemical composition separation of semicrystalline and amorphous EVA copolymers. In addition, separation is achieved from the respective homopolymers. We have found that Gradients of 1,2,4-trichlorobenzene/cyclohexanone, decalin/cyclohexanone, and decalin/1-decanol enable the selective elution of the copolymers from silica gel at 140 °C. The EVA copolymers elute in dependence of their content of the polar vinyl acetate comonomer....

  • Separation of Ethylene−Vinyl Acetate Copolymers by High-Temperature Gradient Liquid Chromatography
    Macromolecules, 2007
    Co-Authors: Andreas Albrecht, Robert Brüll, And Tibor Macko, Harald Pasch
    Abstract:

    Ethylene−vinyl acetate (EVA) copolymers can be semicrystalline or amorphous materials, depending on their chemical composition. A variety of different methods were used for the analysis of the chemical composition distribution of these copolymers, which in general were time- and labor-consuming and could be applied only for a limited range of compositions. In the present work a novel chromatographic method is presented that can be used for chemical composition analysis regardless of the composition of the copolymer. High-Temperature Gradient HPLC has been found to be suitable for chemical composition separation of semicrystalline and amorphous EVA copolymers. In addition, separation is achieved from the respective homopolymers. We have found that Gradients of 1,2,4-trichlorobenzene/cyclohexanone, decalin/cyclohexanone, and decalin/1-decanol enable the selective elution of the copolymers from silica gel at 140 °C. The EVA copolymers elute in dependence of their content of the polar vinyl acetate comonomer....

  • Polyolefin Characterization: The First International Conference on Polyolefin Characterization - Separation and Characterization of Ethylene‐Propylene Copolymers by High‐Temperature Gradient HPLC Coupled to FTIR Spectroscopy
    Macromolecular Symposia, 2007
    Co-Authors: Andreas Albrecht, Lars-christian Heinz, Dieter Lilge, Harald Pasch
    Abstract:

    The chromatographic separation of ethylene-propylene (EP) copolymers with regard to chemical composition was accomplished by a new technique - High-Temperature Gradient HPLC. Using a mobile phase of ethylene glycol monobutylether (EGMBE) and 1,2,4-trichlorobenzene (TCB), and silica gel as the stationary phase, copolymers with different ethylene contents were separated according to their chemical compositions. Using a sample solvent of n-decanol and a column Temperature of140°C, chromatographic conditions were established that correspond to separation in a precipitation-redissolution mechanism. With the aim to obtain further information on the separation process, the HPLC system was coupled to FTIR spectroscopy through a LC-Transform interface. The FTIR data confirmed that the copolymers were separated according to the ethylene content of the eluted samples.

Abdelkrim Talbi - One of the best experts on this subject based on the ideXlab platform.

  • High Temperature Gradient micro-sensors array for flow separation detection and control
    Smart Materials and Structures, 2019
    Co-Authors: Cécile Ghouila-houri, Abdelkrim Talbi, Romain Viard, Quentin Gallas, Eric Garnier, Alain Merlen, Philippe Pernod
    Abstract:

    This paper reports the use of an array of calorimetric micro-sensors that perform bidirectional measurement of wall shear stress, for flow separation detection and control. The sensors design is hot-wire like with three parallel micro wires suspended over a micro-cavity and mechanically supported using periodic perpendicular micro-bridges. The micro-sensors were implemented on a flexible packaging and characterized in a turbulent boundary layer wind tunnel on a flat plate. An array of twelve micro-sensors were then implemented in a flap model designed for active flow control experiments and equipped with pulsed jet actuators. The work included the design and manufacturing of appropriate miniaturized electronics. Without control, the micro-sensors successfully detected the natural flow separation and the flow separation point moving from the trailing edge to the leading edge as the angle of the flap increased. Finally, the micro-sensors characterized the efficiency of the active flow control for avoiding separation.

  • MEMS High Temperature Gradient sensor for skin-friction measurements in Highly turbulent flows
    2019 IEEE SENSORS, 2019
    Co-Authors: Cécile Ghouila-houri, Abdelkrim Talbi, Romain Viard, Quentin Gallas, Eric Garnier, Pascal Molton, Jérôme Delva, Alain Merlen, Philippe Pernod
    Abstract:

    This paper presents and discusses the results obtained with a MEMS High Temperature Gradient sensor for time-averaged and fluctuating skin-friction measurements in Highly turbulent flows. Designed as a robust wall-mounted suspended hot-wire structure, the micro-sensor showed a High Temperature variation for low power consumption. Successfully implemented into two air wind tunnels, the sensor was tested for velocities going up to 270 m/s, mean velocity of airliner cruise flights, and corresponding to a shear stress of 150 Pa. The microsensor thereby demonstrated its value for measuring turbulence in aerodynamic applications, particularly in aeronautics.

  • High Temperature Gradient nanogap-Pirani micro-sensor with maximum sensitivity around atmospheric pressure
    Applied Physics Letters, 2017
    Co-Authors: Cécile Ghouila-houri, Abdelkrim Talbi, Romain Viard, Quentin Gallas, Eric Garnier, Alain Merlen, Mohammed Moutaouekkil, Omar Elmazria, Philippe Pernod
    Abstract:

    This letter describes and discusses the design and testing of an effcient nanogap Pirani micro-sensor for pressure measurements in a wide range with a maximum sensitivity around atmospheric pressure. The structure combines a substrate-free heated wire and mechanical support using silicon oxide micro-bridges allowing both a constant nanoscale gap between the wire and the substrate and a 1 mm long and 3 µm wide wire. The High aspect ratio of wire provides a uniform heating profile along the wire and contributes to low pressure detection. At the opposite, both the nanoscale gap and the short wire length between two micro-bridges contributes to shift the High pressure limit. Tested between 10 kPa and 800 kPa, the sensor presents a wide measurement range, not fully reached by the experiments, with a maximum of sensitivity close to the atmospheric pressure and performances with up to 38 %/dec sensitivity when operation in constant Temperature mode with an overheat of 20 °C.

  • High Temperature Gradient calorimetric wall shear stress micro-sensor for flow separation detection
    Sensors and Actuators A: Physical, 2017
    Co-Authors: Cécile Ghouila-houri, Abdelkrim Talbi, Romain Viard, Quentin Gallas, Eric Garnier, Alain Merlen, Philippe Pernod
    Abstract:

    The paper describes and discusses the design and testing of an efficient and High-sensitivity calorimetricthermal sensor developed for bi-directional wall shear stress measurements in aerodynamic flows. Themain technical application targeted is flow separation detection. The measurement principle is basedon the forced convective heat transfer from a heater element. The sensor structure is composed of threeparallel substrate-free wires presenting a High aspect ratio and supported by periodic perpendicular SiO2micro-bridges. This hybrid structure takes advantages from both conventional hot-films and hot-wires,ensuring near-wall and non-intrusive measurement, mechanical toughness and thermal insulation tothe bulk substrate, and it allowed to add the calorimetric sensor functionality to detect simultaneouslythe wall shear stress amplitude and direction. The central wire is made of a multilayer structure com-posed of a heater element (Au/Ti) and a thermistor (Ni/Pt/Ni/Pt/Ni) enabling measurement of the heaterTemperature and a layer of SiO2 between them for electrical insulation. The upstream and downstreamwires are thermistors enabling operation in the calorimetric mode. This design provides a High tempera-ture Gradient and a homogeneous Temperature distribution along the wires. The sensor operates in bothconstant current and constant Temperature modes, with a feedback on current enabled by uncouplingheating and measurement. Welded on a flexible printed circuit, the sensor was flush mounted on the wallof a turbulent boundary layer wind tunnel. The experiments, conducted in both attached and separatedflow configurations, quantify the sensor response to a bi-directional wall shear stress up to 2.4 Pa anddemonstrate the sensor ability to detect flow separation.

  • High Temperature Gradient micro sensor for wall shear stress and flow direction measurements
    Applied Physics Letters, 2016
    Co-Authors: Cecile Ghouilahouri, Abdelkrim Talbi, Romain Viard, Eric Garnier, Alain Merlen, J Claudel, J C Gerbedoen, Q Gallas, P Pernod
    Abstract:

    We present an efficient and High-sensitive thermal micro-sensor for near wall flow parameters measurements. By combining substrate-free wire structure and mechanical support using silicon oxide micro-bridges, the sensor achieves a High Temperature Gradient, with wires reaching 1 mm long for only 3 μm wide over a 20 μm deep cavity. Elaborated to reach a compromise solution between conventional hot-films and hot-wire sensors, the sensor presents a High sensitivity to the wall shear stress and to the flow direction. The sensor can be mounted flush to the wall for research studies such as turbulence and near wall shear flow analysis, and for technical applications, such as flow control and separation detection. The fabrication process is CMOS-compatible and allows on-chip integration. The present letter describes the sensor elaboration, design, and micro-fabrication, then the electrical and thermal characterizations, and finally the calibration experiments in a turbulent boundary layer wind tunnel.