Papers by Xavier Chavanne
The Turbulent Regimes of Rayleigh-Benard Convection
Fluid Mechanics and Its Applications, 1998
A Rayleigh-Benard convection experiment is performed with Helium at low temperature, as the worki... more A Rayleigh-Benard convection experiment is performed with Helium at low temperature, as the working one-phase fluid [1]. Helium is closed in a cylindrical cell 20 cm high and 10 cm in diameter. Three experimental parameters, independently adjustable, and accurately measured for each fixed condition, allow to study the Rayleigh Benard problem from the conductive regime up to the turbulent convective one. These parameters are: i) the average fluid density in the cell, measured with a 0.7% precision (from 8 g/m3 up to 135 kg/m3 as well as close to the critical point: 69.6 kg/m3, Tc = 5.1953 K, Pc = 2.275 bars); ii) the mean absolute temperature (from 2 K up to 8 K) controlled within a 0.1 mK stability and measured with a 2 mK absolute accuracy; iii) the temperature gradient along the cell height, ΔT (from less than 1 mK up to 5 K), adjusted via the heating power applied on the bottom cell plate, and measured with a 20 mK resolution, 1% uncertainty thermocouple. Two thermometers of 200.tm size and 2 mm vertically apart of each other are located in the cell, at half height and half way between the centre and the wall.
A New Device for <i>In Situ</i> Measurement of an Impedance Profile at 1–20 MHz
IEEE Transactions on Instrumentation and Measurement, Jul 1, 2010
This paper describes a new instrument dedicated to determining the vertical profile of the admitt... more This paper describes a new instrument dedicated to determining the vertical profile of the admittance of a sensor embedded in a medium, such as soil. The instrument consists of two conductive parallel cylinders with a separation between axes on the order of 10 cm to scan a large volume of the medium. The device works at frequencies in the range
Measurement of Relative Permittivity in Controlled Soils using Three Electromagnetic Sensors : HYMENET, TDR and Resonant Cavity
AGUFM, Dec 1, 2014
The Turbulent Regimes of Rayleigh-Benard Convection
Springer eBooks, 1998
A Rayleigh-Benard convection experiment is performed with Helium at low temperature, as the worki... more A Rayleigh-Benard convection experiment is performed with Helium at low temperature, as the working one-phase fluid [1]. Helium is closed in a cylindrical cell 20 cm high and 10 cm in diameter. Three experimental parameters, independently adjustable, and accurately measured for each fixed condition, allow to study the Rayleigh Benard problem from the conductive regime up to the turbulent convective one. These parameters are: i) the average fluid density in the cell, measured with a 0.7% precision (from 8 g/m3 up to 135 kg/m3 as well as close to the critical point: 69.6 kg/m3, Tc = 5.1953 K, Pc = 2.275 bars); ii) the mean absolute temperature (from 2 K up to 8 K) controlled within a 0.1 mK stability and measured with a 2 mK absolute accuracy; iii) the temperature gradient along the cell height, ΔT (from less than 1 mK up to 5 K), adjusted via the heating power applied on the bottom cell plate, and measured with a 20 mK resolution, 1% uncertainty thermocouple. Two thermometers of 200.tm size and 2 mm vertically apart of each other are located in the cell, at half height and half way between the centre and the wall.
Scientific methodology for Telecom services energy consumption and CO2 emission assessment including negative and positive impacts
ABSTRACT The France Telecom operator is highly involved in environmental preservation and part of... more ABSTRACT The France Telecom operator is highly involved in environmental preservation and part of it, is the scientific studies of ICT impacts associated with an active contribution to standardization bodies, observatories, groups, fora and initiatives such as ETSI and ITU-T. This paper describes France Telecom and university common research work in this field and how it can help standardization works. All these methods will help to determine holistic negative impact of ICT, but also the positive impact by dematerialization in a realistic way. Then it is possible to calculate the balance and the so-wished gain by using ICT. The paper will also compare the different Key Performance Indicators that can be calculated by using the impact results such as ICT power consumption reduction, ICT gain on other sectors, ICT contribution to the effort on global consumption and CO2 reduction targets. Finally, the paper should not be complete without indicating some new paradoxes that need much more studies: intensity decrease may hide an absolute value increase, manufacturing optimization and green label may increase the global consumption, the sustainable development level can limit the absolute reduction.
Turbulent Rayleigh–Bénard convection in gaseous and liquid He
Physics of Fluids, May 1, 2001
In this article we deal with the turbulent regimes of Rayleigh–Bénard convection, namely the 2/7 ... more In this article we deal with the turbulent regimes of Rayleigh–Bénard convection, namely the 2/7 regime and beyond. An experiment with He at low temperature allows us to explore a large Rayleigh number (Ra) range up to 2×1014, under Boussinesq conditions, while the Prandtl number (Pr) is equal to and larger than 0.7. Calorimetric measurements evidence a departure from the 2/7 regime above Ra=1011 toward a new regime where the heat transfer is enhanced. Local measurements with two nearby thermometers allows us to relate this change to a laminar–turbulent transition of the velocity boundary layer induced by the large-scale flow near the walls of the cell. The features of the observed new regime match those of the ultimate regime predicted by R. Kraichnan [Phys. Fluids 5, 1374 (1962)] at moderate Pr; in particular, our experimental data show that the thermal boundary layer lies inside the viscous sublayer of the turbulent boundary layer.
European Journal of Environmental and Civil Engineering, Oct 19, 2022
The article describes a modern system of control and communication integrated in an in-situ soil ... more The article describes a modern system of control and communication integrated in an in-situ soil sensor to make it autonomous in operation, energy and data transfer at low cost. Network of such sensors can monitor continuously soil moisture over a catchment with low maintenance. A recent industrial standard of radio communication, Long Range Wide Area Network (LoRaWAN) is presented. It permits rapid deployment of a sensor in a remote observatory, and the transfer in real time of sensor data to a central web-accessed database, via a LoRaWAN receiver, or gateway, 12 km away. In this situation transmission loss can reach a rate of 30%. Good quality antenna can lower it below 5% without extensive cost. Double messaging and other transmission algorithms are a possibility, taking into account consumption. Currently, sensors measuring one point every ten minutes can last seven months with four cheap AA alkaline batteries. Further gains would increase lifetime in same conditions by 30%.
Helium gas turbulence experiments in Grenoble: Techniques and Results
Springer eBooks, 1998
We discuss the new experimental approach of turbulence offered by the use of gaseous 4He around 4... more We discuss the new experimental approach of turbulence offered by the use of gaseous 4He around 4 K. Both the intrinsic properties of the working fluid and the possibilities of cryogenic instrumentation give access to a wide range of control parameters. Examples of new transitions are described in open jet flow and in Rayleigh-Benard experiments.
Cryogenic turbulence experiments
HAL (Le Centre pour la Communication Scientifique Directe), Jun 27, 2000
International audienceCryogenic turbulence experiments are presente
De la détermination du rendement des filières énergétiques
Comptes Rendus Geoscience, Jul 1, 2007
ABSTRACT
European Journal of Environmental and Civil Engineering, Jan 4, 2019
We have developed a permittivity-based sensor using a new and more accurate measurement technique... more We have developed a permittivity-based sensor using a new and more accurate measurement technique. We now investigate the optimum geometry of sensor electrodes to apply models of conversion of medium permittivity into its water content (and salinity), while accounting for field constraints of compactness and simplicity. Models assume medium volume sampled by sensor to be large enough to consider a quasiuniform permittivity. Using this hypothesis, and verifying ex-post its consistency, we carried out an exhaustive study of sample volume dependence on electrode geometry. In particular, we examine the role of electrode diameter, oversight by previous works. Besides, our approach permits a direct experimental validation with profiles of sensor sensitivity. For a two-rod design with electrode spacing D and diameter Φ, sample-volume size and localization is determined by the ratio α = Φ/D. For α lower than 0.25 or thin electrodes-a geometry extensively studied and commonly encountered-theory and measurements show that the volume is concentrated around electrode surface. As α is increased it becomes localized between electrodes with a more uniform sensitivity, like for a parallel-plate capacitor. Volume size at fixed D is also assessed, with its highest value between α = 0.30 and 0.50. We adopted this range for our sensors.
Biomass & Bioenergy, Oct 1, 2011
The article assesses the energy R required by a system to transform a cereal or sugar plant into ... more The article assesses the energy R required by a system to transform a cereal or sugar plant into ethanol. From the specific consumption r j of each process j and its weight w j in the system, process consumption share R j is deduced and hence R, sum of R j. Depending on w j definition, R j and R are relative to either 100 J of ethanol produced or 100 J of plant harvested. Depending on the nature of r j , R j and R represent either only primary external energies, or all fuel and electricity consumed directly, or external and internal energies. From one definition to another R for average sugar cane based industries is the best or the worst relative to other plants. This results also from the use of cane residues as fuels while operating outdated processes. Through r j the process based analysis allows to examine for each system the impact of modern processes or different use of residues. All systems benefit except sugar beet based industry close to its best efficiency. This flexibility permits even to build a self-sufficient system where existing processes produce from system resources substitutes to external energies. R becomes an unambiguous definition of a system efficiency. It shows that all agroethanol systems are more consuming than petroleum industry. The system can be expanded to the vehicle stage to compare with alternatives to ethanol such as electricity and biogas. Wheat straw burnt to produce electricity used in an electrical vehicle will present R close to that of petroleum industry.
Sensors, May 28, 2018
The article comments on claims made by Rêgo et al. about the sensor they developed to determine s... more The article comments on claims made by Rêgo et al. about the sensor they developed to determine soil water content and its salinity via the admittance measurement of electrodes embedded in the soil. Their sensor is not based on a self-balanced bridge, as stated, but on a more common technique relying on Ohm's law. A bridge is a zero method of measurement which can provide direct voltages proportional to soil permittivity and conductivity with a high resolution. Thanks to modern electronics the method can be adapted for fast and continuous monitoring in a remote site. Because of this confusion about the different measurement techniques among available admittance or capacitance sensors, we give a succinct review of them and indicate how they compare to the two techniques under discussion. We also question the ability of Rêgo et al.'s current sensor to determine both soil water content and salinity due first to instrument biases and then to the soil complexity as a dielectric medium. In particular, the choice of sensor frequencies is crucial in the two steps. In addition, the procedure to determine and account for temperature influences on readings is not presented clearly enough. It is important to distinguish between the effect resulting from electronics sensitivity, and those that are soil-specific. The comment does not invalidate the design of the sensor, but indicates points, especially parasitic contributions, which must be dealt with to avoid major errors.
Biomass & Bioenergy, Jul 1, 2011
The article assesses the energy R required by a system to transform a cereal or sugar plant into ... more The article assesses the energy R required by a system to transform a cereal or sugar plant into ethanol. From the specific consumption r j of each process j and its weight w j in the system, process consumption share R j is deduced and hence R, sum of R j. Depending on w j definition, R j and R are relative to either 100 J of ethanol produced or 100 J of plant harvested. Depending on the nature of r j , R j and R represent either only primary external energies, or all fuel and electricity consumed directly, or external and internal energies. From one definition to another R for average sugar cane based industries is the best or the worst relative to other plants. This results also from the use of cane residues as fuels while operating outdated processes. Through r j the process based analysis allows to examine for each system the impact of modern processes or different use of residues. All systems benefit except sugar beet based industry close to its best efficiency. This flexibility permits even to build a self-sufficient system where existing processes produce from system resources substitutes to external energies. R becomes an unambiguous definition of a system efficiency. It shows that all agroethanol systems are more consuming than petroleum industry. The system can be expanded to the vehicle stage to compare with alternatives to ethanol such as electricity and biogas. Wheat straw burnt to produce electricity used in an electrical vehicle will present R close to that of petroleum industry.
Comptes Rendus Geoscience, May 1, 2008
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright
Comptes Rendus Geoscience, Oct 1, 2009
Two original in situ HF techniques of dielectric characterization in two wide bands have been dev... more Two original in situ HF techniques of dielectric characterization in two wide bands have been developed in order to estimate the moisture content of soils by complex impedance measurement. These techniques are based on the capacitive effect (1-20 MHz) and on the propagation of electromagnetic waves at high frequencies (0.1-4 GHz). The two measurement techniques use straight conductors that are inserted into the soil. Specific inversion algorithms were developed to estimate the apparent real permittivity of the soil versus frequency from the complex impedance. The validation of both instruments was made in the laboratory in the presence of dry and wet sands. In situ experiments were also made at high frequencies. These complementary devices should enlarge the range of usual soil moisture measurement techniques. To cite this article:
Sensors, Aug 26, 2014
This paper describes a sensor dedicated to measuring the vertical profile of the complex permitti... more This paper describes a sensor dedicated to measuring the vertical profile of the complex permittivity and the temperature of any medium in which sensor electrodes are inserted. Potential applications are the estimate of the humidity and salinity in a porous medium, such as a soil. It consists of vertically-stacked capacitors along two conductive parallel cylinders of 5 cm in diameter and at a 10-cm distance to scan a significant volume of the medium (∼1 L). It measures their admittances owing to a self-balanced impedance bridge operating at a frequency in the range of 1-20 MHz, possibly 30 MHz. Thanks to accurate design and electronic circuit theory-based modeling, the determination of the admittances takes into account all distortions due to lead and bridge electromagnetic effects inside the sensor when working at high frequencies. Calibration procedures and uncertainties are presented. The article also describes developments to make the present sensor autonomous on digital acquisition, basic data treatment and energy, as well as able to transfer stored data by a radio link. These steps in progress are prerequisites for a wireless network of sensors.
Sensors, May 11, 2017
The article describes a new field sensor to monitor continuously in situ moisture and salinity of... more The article describes a new field sensor to monitor continuously in situ moisture and salinity of a porous medium via measurements of its dielectric permittivity, conductivity and temperature. It intends to overcome difficulties and biases encountered with sensors based on the same sensitivity principle. Permittivity and conductivity are determined simultaneously by a self-balanced bridge, which measures directly the admittance of sensor electrodes in medium. All electric biases are reduced and their residuals taken into account by a physical model of the instrument, calibrated against reference fluids. Geometry electrode is optimized to obtain a well representative sample of the medium. The sensor also permits acquiring a large amount of data at high frequency (six points every hour, and even more) and to access it rapidly, even in real time, owing to autonomy capabilities and wireless communication. Ongoing developments intend to simplify and standardize present sensors. Results of field trials of prototypes in different environments are presented.
European Physical Journal B, Oct 1, 2003
The focusing of acoustic waves is used to study nucleation phenomena in liquids. At large amplitu... more The focusing of acoustic waves is used to study nucleation phenomena in liquids. At large amplitude, non-linear effects are important so that the magnitude of pressure or density oscillations is difficult to predict. We present a calculation of these oscillations in a spherical geometry. We show that the main source of non-linearities is the shape of the equation of state of the liquid, enhanced by the spherical geometry. We also show that the formation of shocks cannot be ignored beyond a certain oscillation amplitude. The shock length is estimated by an analytic calculation based on the characteristics method. In our numerical simulations, we have treated the shocks with a WENO scheme. We obtain a very good agreement with experimental measurements which were recently performed in liquid helium. The comparison between numerical and experimental results allows in particular to calibrate the vibration of the ceramics used to produce the wave, as a function of the applied voltage.
Physical Review Letters, Jun 11, 2001
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Papers by Xavier Chavanne