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International audience; À l’avenir, la culture de plantes supérieures sera un élément clé des systèmes de support de vie biorégénératifs. Cela nécessitera une compréhension approfondie des phénomènes qui jouent un rôle important au cœur du métabolisme des plantes et de leur interaction avec l’environnement. Les plantes sont des organismes complexes qui doivent être étudiés à l’aide de répliques de feuilles. Ceci permet l’étude des phénomènes physiques à la surface des feuilles, sans interactions biochimiques ou biologiques, ni variabilité génétique. Pour évaluer l’influence de la gravité, il est nécessaire de développer des modèles mécanistes précis du comportement des plantes dans l’espace. Cet article de synthèse présente l’état de l’art des répliques foliaires et des phénomènes concomitants, pour une application spatiale.

The aim of this work was to investigate mixing and liquid-to-gas mass transfer of hydrogen in relation to hydrogen production in the dark fermentation process as a function of agitation conditions and digestate viscosity. Experiments were carried out in a baffled mechanically-stirred reactor equipped with a dual-stage impeller using five levels of viscosity. Biohydrogen production was studied using glucose as substrate under controlled pH. Three experimental techniques, namely local conductimetry, chemical decolorization and Planar Laser Induced Fluorescence were used to measure mixing time t m and describe the flow pattern. The effects of inter-impeller clearance and tracer injection position were also studied. Then, k L a H 2 was deduced from dynamic deaeration/aeration experiments. Experimental results showed that biohydrogen production presented a maximum in the transitional flow regime ( Re about 200), and fell under turbulent flow ( Re > 1000). Similarly, the evolution of k L a H 2 was better described by Re than by the volumetric power input, contrary to literature data. Finally, the Damkohler number showed that hydrogen production was limited by liquid-to-gas mass transfer in the laminar regime and that maximum reaction rate could be reached only due to dissolved H2 supersaturation in the liquid phase. Conversely, the steep decrease of H2 production under turbulence conditions could be attributed neither to mass transfer, nor to mixing conditions, highlighting a probable negative interaction between turbulent eddies and biomass aggregates. Regarding k L a ∙ t m , the transitional flow region also approached ideal mixing, which strengthened the conclusion that H2 production was optimized in the transition region in the dark fermentation process.

The water vapor present in the atmosphere may be one of the sources of fresh and clean water. It is well known that 70% of the earth is covered with water. However, only less than 1% of fresh water is of direct use for humankind on earth. Several techniques have been devised to mitigate the availability of fresh water for humans. In this paper, a novel approach has been discussed to study the mass transfer from water vapor on a flat surface, and a moisture harvesting technique has been developed as a non-conventional source using the Peltier module to produce water condensate. The characterization of the flat surfaces has been done for the thermal homogeneity and the temperature gradient. The droplet nucleation process and the mass flux of water vapor from the air on the vertical surface at different temperatures have been devised. The results have been discussed for the mathematical calculation of the Reynolds number, Schmidt number, and Sherwood number using the experimental data. The comparison of experimental and theoretical mass fluxes was presented with an airflow velocity of less than 1.0 ms−1. The airflow on the condensing surface was a mixed type, and the coefficient of proportionality of the fluid flow was calculated as 0.23 for the proposed blunt-faced structure. The outcome was theoretically validated for the rate of condensation of water vapor from humid air and the mass flux produced. The technique developed may have several applications ranging from mass transfer in biotechnology to the nonconventional source of water production.

This work is a contribution to the improvement of the thermal and the dynamic fields of a natural convection indirect solar dryer, composed of a solar flat air heater and a drying chamber, intended for drying agricultural products and medicinal plants. We have studied the effects of size and position of the outlet on the distribution of air and temperature within the drying chamber, containing the figs as a product to be dried. To be more realistic, we have used a user defined function (UDF) subroutine written in [Formula: see text] to integrate the unsteady evolution of a day’s climate data in the Oujda region. This study was achieved by numerical simulations using the ANSYS FLUENT software, in order to optimize the distribution of air and temperature inside the drying chamber, and to choose the best outlet’s position and size for the best efficiency of the dryer. The results show that the optimal outlet position found is in the right corner with a size range of 0.07 to 0.15[Formula: see text]m. The effects of the position and size of the outlet on the air deflection along the trays were also presented and discussed.

JTHT-T6373; International audience

Growing plants in space during long-duration missions will be crucial to ensure functions such as food production, air revitalization, and water purification, and requires an in-depth understanding of plant growth and development processes in reduced gravity. In particular, gas exchange at the leaf surface is considerably reduced because of lack or reduction of buoyancy-driven convection, which can translate into reduced biomass production in the long run. To quantify this impaired gas exchange and biomass production, this study formulates a mechanistic model of these variables in low gravity following a chemical engineering approach. The emphasis here is set on short-term physical response of gas exchange at the leaf surface to gravity and airspeed. A mass balance with stoichiometric limitations enables the computation of mass exchange fluxes, and an energy balance relates them to heat transfer fluxes. Leaf surface temperature and biomass production in the form of dry mass and free water mass are then subsequently computed. The validation of this model on sets of independent data from published parabolic flight experiments is presented and a sensitivity study to different parameters highlights the existence of threshold values for gravity, ventilation, light, and stomatal conductance, which dictate the magnitude of changes in leaf surface temperature and photosynthesis rate. These results show that a mechanistic modeling approach coupled to a dedicated experimental approach are key to identify adequate growth conditions for plants in reduced gravity environments.

International audience; The SPALAX-NG is a new-generation system that is designed to detect radioactive xenon at trace levels in the atmosphere following a nuclear explosion or civilian source release. This new system formed part of a validation program led by the Provisional Technical Secretary of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) Organization. In this study, the first SPALAX-NG unit was tested for six months between October 2018 and April 2019 at the CEA/DIF premises near Paris, France. This test period provided an outstanding opportunity to illustrate the high level of detectability and reliability of the system. The data availability obtained over this period was approximately 99%, which was well above the CTBT Data Availability criteria of 95%. The data reliability was demonstrated by a comparison with a collocated SPALAX-1 unit (former version of SPALAX) and by re-measuring several samples at the CTBT-certified French laboratory FRL08. The high sensitivity to the detection of the four relevant radioxenon isotopes was fully demonstrated and enabled the recording of a major dataset for western Europe. A large set of isotopic ratios was measured, which enabled the discrimination criteria between civilian sources and nuclear test signatures to be refined.

Including plants in bioregenerative life-support systems enables simultaneous food production and water and air recycling, while closing cycles for water, oxygen, nitrogen, and carbon. To understand and predict higher plant behavior for a wide range of environmental conditions, including reduced gravity levels, a mechanistic physical model is being developed. The emphasis is set on the influence of gravity levels and forced convection on higher plant leaf gas exchanges, which are altered by reduction of free convection in lower gravity environments, such as microgravity or martian and lunar gravities. This study highlights the significance of understanding leaf boundary layer limitations and ultimately will lead to complete mechanistic modeling of mass and energy balances on plant growth in reduced gravity environments.

The present work focuses on the numerical simulation of isothermal and weakly compressible Poiseuille flow in a planar channel using the Lattice Boltzmann method with multiple times of relaxation (MRT-LBE) coupled to the Finite Difference method (FDM). The active fluid considered is the air under low Mach number assumption. The flow is two-dimensional, laminar and all the physical properties are constants except the density which varies in the sense of the Boussinesq approximation. The effects of the compressibility, the inclination angle and the Reynolds number on the dynamical and thermal fields are studied numerically. The results are presented in terms of streamlines, isotherms and transverse velocity.

International audience; An ultra-compact and unshielded spectrometer for analysis of atmospheric xenon radionuclides has been developed: the MARGOT system. This system works at ambient temperature and high pressure, and has a 54.3 cm$^3$ inner active volume. Atmospheric xenon radionuclide activities are determined with the electron-photon coincidence technique using both NaI(Tl) detectors and large pixellized Si-PIN detectors. The MARGOT system integrates an enhanced version of the PIPSBox™, Geant4 simulation and first calibration results are discussed.

Hydrogen production by dark fermentation (DF) from wastewater, food waste, and agro-industrial waste combines the advantages to be renewable, sustainable and environmentally friendly. But this attractive process involves a three-phase gas-liquid-solid system highly sensitive to mixing conditions. However, mixing is usually disregarded in the conventional strategies for enhancing biohydrogen productivity, even though H 2 production can be doubled, e.g. versus of reactor design (0.6–1.5 mol H 2 /mol hexose). The objective of this review paper is, therefore, to highlight the key effects of mixing on biohydrogen production among the abiotic parameters of DF. First, the pros and cons of the different modes of mixing in anaerobic digesters are described. Then, the influence of mixing on DF is discussed using recent data from the literature and theoretical analysis, focusing on the multiphase and multiscale aspects of DF. The methods and tools available to quantify experimentally the role of mixing both at the local and global scales are summarized. The 0-D to 3-D strategies able to implement mixing in fermentation modeling and scale-up procedures are examined. Finally, the perspectives in terms of process intensification and scale-up tools using mixing optimization are discussed with the issues that are still to be solved.

The study of higher plant growth in space started in the 1950s both on the Russian and the American sides. The first experiments were intended to assess whether plants could grow outside Earth and to determine what differences there were between spaceflight-grown and Earth-grown plants. As plant-growth hardware started to adapt to spaceflight, more opportunities for plant experiments in space became available. Direct microgravity effects started being differentiated from confinement effects and Earth orbit started to become a laboratory where plants could be grown without the influence of Earth gravity. Experiments have shown that, with adapted ventilation, plant growth in space is similar to plant growth on Earth in 1 g, except for some morphological traits. However, only small-scale experiments on plant growth were performed in Earth orbit, which provided insufficient data on crop yield for reduced gravity environments. Challenges remain to grow plants in space, in terms of nutrient delivery, li...

Nowadays, many performing insulation materials are available on the market. However, their expected thermal performance can be affected by many sources of uncertainty due to random errors that can occur during the manufacturing and the measurement processes. In addition, the thermal performance is strongly affected by another source of uncertainty related to the insulation laying process. As a matter of fact, defects in insulation panels are introduced either for practical reasons or due to a lack of rigor of workers. These errors are still not yet properly considered for simulation, although they result in significant heat losses. This work aims at investigating the impact of four common workmanship errors on the thermal performance of insulation panels. A coupling between experimental measurements and finite element modeling allows us to evaluate the effective thermal conductivity of insulations in presence of defects. The uncertainty analysis allows us to quantify the dispersion of insulation conductivity according to different types and sizes of defects, showing that flexible materials seem to be more affected by the defects. For simulation purpose, analytical models are proposed to assess the effective thermal conductivity in terms of size and type of defects. The numerical application to insulated wall shows the impact of each defect on the energy consumption, where deep grooves and openings are found to be strongly affecting the insulation performance.

The purpose of this paper is to develop a numerical scheme based on the MRT-D2Q9 model for fluid velocity and the MRT-D2Q5 cross model for the temperature to study the natural convection phenomenon in a differentially heated square enclosure containing air. The present work aims to prove the accuracy and the capacity of this model to predict the thermodynamics phenomena. In fact, the main goal consists to demonstrate the efficiency of the double population approach based on new MRT-LBM scheme in the assessment of laminar and transitional flows in natural convection case for different Rayleigh numbers (up to 108). The numerical results of the present work were successfully checked for accuracy and are in satisfactory agreement with those available in literature. The results analysis shows that the present method has proven its ability to handle similar problem.

An ultra-compact and unshielded spectrometer for analysis of atmospheric radioxenons has been developed. This system works at ambient temperature and has a 58 cm3 inner active volume. Atmospheric radioxenons activities are determined with electron/photon coincidence technique using both NaI(Tl) detector and large pixellized Si-PIN detector. The performances of the detection system without shielding in terms of Minimal Detectable Activities are below 65 mBq for a 12 h acquisition, for all radioxenons of interest. An enhanced version of the prototype presented here is already under development: the Mobile Analyzer for Radioactive Gases OuTflows (MARGOT) system.

In mechanically stirred tanks, turbulent flow conditions have already been shown to impair biohydrogen production through dark fermentation even when the dimensionless Reynolds number ( Re ) is between 103 and 104. The aim was, therefore, to investigate the local hydrodynamic conditions encountered by bacterial aggregates in a fully baffled 2-L bioreactor equipped with a double stage Rusthton turbine in which dark fermentation had already been extensively studied. Both experimental and numerical tools (namely, Particle Image Velocimetry and Computational Fluid Dynamics) were applied to analyze the flow pattern and determine the main features of the turbulent flow. Experiments and simulations involved two levels of viscosity and three levels of agitation speed, corresponding to Re between 2.2·103 and 1.1·104 and power requirements P / V between 0.6 and 87 W/m3. A good agreement between simulated and experimental data was achieved, including velocity, turbulent kinetic energy and turbulent dissipation rate. Comparing the size of bacterial aggregates to Kolmogorov length scale, experimental and numerical results demonstrated that bacterial aggregates could be exposed to potentially damaging hydromechanical stress under turbulent flow in the vicinity of the impeller when Re = 2.2·103 and that this region rapidly expanded to the whole bioreactor when Re increased, which could explain the rapid fall of biohydrogen production vs. Re in the turbulent flow regime.

The PIPSBox is a new high resolution electron spectrometer composed of two Si-PIN detectors developed by CEA. It is designed for the measurement of radioxenons by means electron/photon coincidences when coupled to a NaI(Tl) or HPGe detector. Alternatively, electron/electron (or Si/Si) coincidences can be studied when focusing on events depositing energy in its two Si-PIN detectors simultaneously. In this paper, such Si/Si coincidence measurements are studied. Especially, it is shown (using Monte-Carlo simulations) that the Si/Si background coincidence spectrum is dominated by secondary cosmic muons. Finally, the cosmic veto efficiency of the γ3 spectrometer (a recently developed low-background ground-based photon spectrometer (Cagniant et al., 2015)) was estimated to be 99.0±0.7% thanks to Si/Si coincidence measurements inside its shielding.

In the context of the verification regime of the Comprehensive nuclear Test ban Treaty (CTBT), CEA is developing a new generation (NG) of SPALAX™ system for atmospheric radioxenon monitoring. These systems are able to extract more than 6cm(3) of pure xenon from air samples each 12h and to measure the four relevant xenon radioactive isotopes using a high resolution detection system operating in electron-photon coincidence mode. This paper presents the performances of the SPALAX™ NG prototype in operation at Bruyères-le-Châtel CEA centre, integrating the most recent CEA developments. It especially focuses on an innovative detection system made up of a gas cell equipped with two face-to-face silicon detectors associated to one or two germanium detectors. Minimum Detectable activity Concentrations (MDCs) of environmental samples were calculated to be approximately 0.1 mBq/m(3) for the isotopes (131m)Xe, (133m)Xe, (133)Xe and 0.4 mBq/m(3) for (135)Xe (single germanium configuration). The detection system might be used to simultaneously measure particulate and noble gas samples from the CTBT International Monitoring System (IMS). That possibility could lead to new capacities for particulate measurements by allowing electron-photon coincidence detection of certain fission products.

The γ(3) setup has been designed as a versatile, high sensitivity spectrometry platform. State-of-the art techniques have been implemented to reduce its background to minimum level even though the system is installed at ground level. The shield design and background performance of the setup are presented. The spectrometer is composed of three identical HPGe detectors for high detection efficiency or coincidence measurement and can accommodate several sample geometries. Its shield includes three layers of increasing purity lead, a cosmic veto, an inner borated polyethylene layer, and a radon-free gas injection system. The spectrometer normalized background count rate is 4.4 counts per minutekgGe(-1) (in the 40-2500keV energy range). Its background characteristics, cosmic veto efficiency, and radon-free gas injection performances are discussed.

The aim was to investigate the influence of mixer design and operating conditions in an anaerobic digester designed for BioH 2 production. Distributive mixing was studied through different dual-impeller configurations with various impeller size, clearance and types. Advanced optical experimental techniques, such as Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) were used to determine mixing time and the flow pattern in the bioreactor. PLIF, decolorization and conductimetric methods were compared for mixing analysis. CFD was used to achieve a more detailed analysis of hydrodynamics and mixing. Experiments and simulations were limited to power input lower than 10 W/m 3 , which is a necessary condition to achieve sustainability and corresponds to 50–150 rpm in this work. Nine designs of dual-impeller configurations were compared in an unbaffled tank. Experimental results suggest that mixing was strongly modified by changing the geometry of the lower impeller and, to a lesser extent, the off-bottom clearance and the injection position for dual-impeller devices. Macromixing time t m derived from the conductimetric technique always agreed with PLIF, but was higher than values from chemical decolorization when an axial-tangential flow pattern validated by PIV and CFD data was reported. CFD was able to predict the mean flow and the turbulence features, so that their respective role on mixing could be compared. Finally, a non-conventional mixer dual-impeller device was shown to counterbalance lower turbulence and power input by an enhanced axial flow circulation that made t m weakly dependent on the position of the injection and favored dispersive mixing.

The purpose of this study is to investigate the natural convection in a Γ-shaped enclosure using hybrid thermal lattice Boltzmann method (HTLBM). The vertical walls are at cold temperature while the horizontal walls are adiabatic. In our mathematical formulation, a 2D Multiple Relaxation Time-Lattice Boltzmann Equation (MRT-LBE) D2Q9 and Finite Difference Method (FDM) are applied for fluid velocity and temperature respectively. Results are presented, for different step size and for Rayleigh number varying from 103 to 106, in form of isotherms, streamlines and Nusselt number. It is observed that the step height and the buoyancy force, induced by the temperature difference, significantly affect the velocity and temperature distributions and the rate of heat transfer from the heated wall.

Radioactive xenon (mainly 131m Xe, 133 Xe, 133m Xe and 135 Xe) are tracked as markers of nuclear weapons testing. The CEA has developed the PIPSBox, a measurement cell able to detect electrons emitted by xenon nuclides. Combined with an ultra-low background γ spectrometer, electron detection capacities allow reaching minimum detectable activities (MDA) for a 3-day long measurement of about 0.5 mBq for the four xenon radionuclides. Compared to a classical measurement cell, MDAs are improved by a factor of 2–4.

Nowadays, insulation is increasingly used for houses and buildings for its economic and environmental advantages. The performance of an insulated construction depends mainly on the thickness and the properties of the used insulation material. However, this performance is subjected to various uncertainties related for instance to the manufacturing process of the material and to the different workmanship errors that affect the thermal resistance of the insulated construction. In practice, these uncertainties are still rarely considered in energy analysis. Nevertheless, beyond a given level of uncertainties, the insulation system does not perform as expected which induces additional unexpected costs related to energy and pollution. This work aims first, at showing the impact of these uncertainties on the reliability of the insulated construction and second, at developing a new formulation of the global cost for the design of insulation system considering additional costs related to user and environment. The proposed cost formulation allows us to provide a better estimation of the payback period. Three configurations are considered with different insulation schemes in order to show the impact of uncertainties and indirect costs on the insulation performance.

The ability to quantify isotopic ratios of 135, 133 m, 133 and 131 m radioxenon is essential for the verification of the Comprehensive Nuclear-Test Ban Treaty (CTBT). In order to improve detection limits, CEA has developed a new on-site setup using photon/electron coincidence (Le Petit et al., 2013. J. Radioanal. Nucl. Chem., DOI : 10.1007/s 10697-013-2525-8.). Alternatively, the electron detection cell equipped with large silicon chips (PIPS) can be used with HPGe detector for laboratory analysis purpose. This setup allows the measurement of β/γ coincidences for the detection of 133 Xe and 135 Xe; and K-shell Conversion Electrons (K-CE)/X-ray coincidences for the detection of 131m Xe, 133m Xe and 133 Xe as well. Good energy resolution of 11 keV at 130 keV and low energy threshold of 29 keV for the electron detection were obtained. This provides direct discrimination between K-CE from 133 Xe, 133m Xe and 131m Xe. Estimation of Minimum Detectable Activity (MDA) for 131m Xe is in the order of 1 mBq over a 4 day measurement. An analysis of an environmental radioxenon sample using this method is shown.

INGENIERIE+SAG:YSC:DFA; The number and strength of adsorption sites for Xe in silver-modified zeolites are estimated from isotherm measurements at various temperatures over a broad range of pressure (from 1 ppm to atmospheric pressure). Fully and partially exchanged silver zeolites were synthesized starting from Na-ZSM-5(25), Na-ZSM-5(40), Na-Beta, NaX, and NaY. We have discovered that silver-modified zeolites may present one or two distinct adsorption sites depending on the nature of the material and silver loadings. The strongest adsorption sites are characterized by isosteric heat of adsorption in the order of -40 to -50 kJ.mol(-1). For Pentasil-type zeolites, we observe a linear 2:1 correlation between the total amount of silver and the number of strong sites. The highest concentration of strong sites is found for fully silver exchanged ZSM-5 (5.7 X 10(-4) mol/g), which presents the largest silver content for Pentasil-type zeolite. The equilibrium constant of Ag-ZSM-5 at low pressure is about 50 times larger than that of AgX. Qualitative correlations were established between Xe adsorption isotherms and Xe NMR signals. We show that Xe NMR could be used as a quantitative method for the characterization of the strength and of the number of strong Xe adsorption sites on silver-exchanged zeolites. The numbers of strong adsorption sites responsible for the Xe adsorption at 10-1000 ppm can be determined by the length of the plateau observed at low Xe uptake. In practice, our findings give guidelines for the discovery and optimization of silver-loaded zeolites for the capture of Xe at ppm levels. It appears that the amount of silver is a key parameter. Silver-modified ZSM-5 shows adsorption capacities 2-3 orders of magnitude larger than currently applied adsorbents for atmospheric Xe capture.

This work deals with the analysis and the optimization of a dual-impeller design in terms of mixing, hydrodynamics, mass transfer properties and power input in a mechanically stirred digester devoted to biohydrogen production through acidogenic fermentation of lignocellulosic waste. Various mixer designs involving Rushton turbines, an Elephant Ear impeller and a marine propeller, were compared. Experimental data were successfully confronted to CFD-based simulations used to reveal the respective roles of impeller type, geometry and clearance. The results showed that the flow pattern was strongly influenced by the off-bottom and inter-impeller clearances, and by the size and type of the lower impeller. Straw suspension was enhanced by a small disk turbine with a low off-bottom clearance and a large inter-impeller clearance that promoted an axial flow circulation together with a small mixing time due to the interaction with the larger turbine used as the upper impeller. Conversely, kLa evolution was weakly dependent on impeller design, position, and rotation speed until a deep vortex formed on the free surface, showing that power input was too weak to enhance liquid-to-gas mass transfer. Finally, the design including an Elephant Ear turbine as the upper impeller and a smaller Rushton turbine as the lower impeller was selected as the best compromise between distributive and dispersive mixing, while the objective of a power input lower than 10 W/m3 was achieved.

A numerical investigation to simulate the fluid flow and heat transfer in a two-dimensional horizontal channel containing a multi heated physical rectangular bodies is conducted using hybrid thermal lattice Boltzmann method (HTLBM). A combination between the Multiple Relaxation Time-Lattice Boltzmann Equation (MRT-LBE) D2Q9 for fluid velocity and Finite Difference Method (FDM) for temperature is used. In the plane channel, the bodies are placed in a side-by-side arrangement and normal to the incoming flow. The air flow is assumed to be laminar and incompressible. Special attention is paid to investigate the effect of the Reynolds number on the fluid flow and the heat transfer, where the dimensions and the distance between the bodies are fixed.

International audience; The phenomenon of heat and mass transfer by condensation of water vapour from humid air involves several key concepts in aerobic bioreactors. The high performance of bioreactors results from optimised interactions between biological processes and multiphase heat and mass transfer. Indeed in various processes such as submerged fermenters and solid-state fermenters, gas/liquid transfer need to be well controlled, as it is involved at the microorganism interface and for the control of the global process. For the theoretical prediction of such phenomena, mathematical models require heat and mass transfer coefficients. To date, very few data have been validated concerning mass transfer coefficients from humid air inflows relevant to those bioprocesses. Our study focussed on the condensation process of water vapour and developed an experimental set-up and protocol to study the velocity profiles and the mass flux on a small size horizontal flat plate in controlled environmental conditions. A closed circuit wind tunnel facility was used to control the temperature, hygrometry and hydrodynamics of the flow. The temperature of the active surface was controlled and kept isothermal below the dew point to induce condensation, by the use of thermoelectricity. The experiments were performed at ambient temperature for a relative humidity between 35-65% and for a velocity of 1.0 ms(-1). The obtained data are analysed and compared to available theoretical calculations on condensation mass flux.

Long-term flights or the establishment of permanent bases in space provide serious challenges for life support systems. Plants are essential companion life forms for such space missions, where human habitats must mimic the cycles of life on earth to generate and recycle food, oxygen and water. Nowadays, the chemical–mechanical recycling systems used in the international space station are much more compact, less labour intensive and more reliable than plant-based systems, but these systems would be too expensive for the long-term human exploration. In order to improve living conditions for humans and plants, we need an accurate characterisation of the mass transfer phenomena related to condensation of humid air. We are interested in developing an experimental protocol, which would help us to establish a theoretical model describing the heterogeneous transfers along a wall or a plant in an air-conditioned environment. Initially, we started in dry conditions by measuring the velocity profiles within the boundary layer that develop on a horizontal or a vertical flat plate in a wind tunnel. The velocity ranged from 0.5 to 2.5 m s−1. Existing coupled heat and mass transfer measurement results relevant to our applications are discussed.

Within the frame of Comprehensive Nuclear-Test Ban Treaty (CTBT), this paper deals with the development of the new techniques necessary for the xenon monitoring requested by the CTBT. An automatic system called SPALAX™, devoted to the on-site sampling and measurement was developed by French atomic energy commission (CEA). Analytical methods and equipments have been studied at our laboratory, using dual X-γ-spectrometry in order to get independent means with better sensitivity within a robust quality assurance program. In the case of a wide number of potential existing sources and depending on meteorological conditions, several solutions can be arrived at.

The aim of this work was to study an externally-submerged membrane bioreactor for the cyclic extraction of volatile fatty acids (VFAs) during anaerobic fermentation, combining the advantages of submerged and external technologies for enhancing biohydrogen (BioH2) production from agrowaste. Mixing and transmembrane pressure (TMP) across a hollow fiber membrane placed in a recirculation loop coupled to a stirred tank were investigated, so that the loop did not significantly modify the hydrodynamic properties in the tank. The fouling mechanism, due to cake layer formation, was reversible. A cleaning procedure based on gas scouring and backwashing with the substrate was defined. Low TMP, 10(4)Pa, was required to achieve a 3Lh(-1)m(-2) critical flux. During fermentation, BioH2 production was shown to restart after removing VFAs with the permeate, so as to enhance simultaneously BioH2 production and the recovery of VFAs as platform molecules.

The effects on the spectral power density (SPD) of randomized pulse width modulation (RPWM) waveforms by the choice of different probability distribution laws are investigated. The distribution laws under studied are symmetric uniform, normal, laplace, and parabolic. A comparison method, based on a normalized deviation with respect to the uniform distribution law, is devised. It is shown, by way of analytical derivation and simulations, that uniform distribution produces power spectrum comparable to those generated by other relatively more complex distributions under studied. Significantly, it means that uniform distribution, which is the simplest to implement, is the preferred probability law for randomization in a RPWM scheme.

Today, the political and regulatory framework related to the building sector is more demanding as it remains the principal source of air pollution leading to global warming. Therefore, it is important to have a better control on the energetic performance of the building envelope in order to control the consumption. This paper presents a methodology allowing us to obtain optimal designs of the envelope considering different kinds of uncertainties mainly those related to climate changes, material deterioration and man-made defects. The time-dependent uncertainties are considered as random processes while the time-invariant variability related to defects is considered as random variable. The results show the impact of considering these uncertainties on the long term reliability of the system and give different optimal designs according to the considered climatic scenario.

The purpose of this paper is to numerically examine the conjugate surface radiation-natural convection heat transfer in a 2D differentially heated enclosure with an inner square body, which generates heat. The numerical model is based on the coupling of the MRT-lattice Boltzmann model with finite difference method (FDM). The first one is used to compute the velocity field, while the second is adopted to obtain the temperature field. Various key parameters are studied, such as Rayleigh number (10 3 ≤ Ra ≤ 10 6 ), temperature-difference ratio ΔT* (0 ≤ ΔT* ≤ 50), body’s thermal conductivity (0 K s Ra .

Laboratory experimentation, numerical simulation, and energy-stability theory are used to examine the effect of interface deformation on the onset of oscillatory thermocapillary convection in half zones. Experiments are performed to map the stability boundaries marking the onset of oscillatory flow, modifying the free-surface deformation by adjusting the volume of liquid in the bridge. The stability results presented here along with those of other researchers [Monti et al., Proceedings of the 43rd Cong. Int. Artro. Fed. (1992); Hu et al., J. Cryst. Growth 142, 379 (1994)] show that free-surface curvature can have a pronounced influence on flow stability. Steady, axisymmetric flow simulations are computed using the commercial code FIDAP to model the conditions of the experiments, and reveal that flow structure near the stability boundary is sensitive to several parameters. Energy theory is applied to these simulations to determine sufficient conditions for stability. Comparisons between the theoretical and...

The condensation phenomenon of humid air on solid substrates can occur in many applications, and it is known as one of the most difficult problem to deal with for the improvement of the quality of air in a closed environment. The present study was motivated by the investigation of the coupling between ventilation and condensation inside Controlled Ecological Life Support Systems (CELSS), as it has an important role for higher plants growth in greenhouses and living conditions in manned spacecraft cabins, particularly in long duration space flights or in future space bases. It is well known that the enhancement of the gas exchange with leaves and the growth of plants are dependent on the organoleptic and/or the surrounding thermo-physical factors. Insufficient air movement around plants and condensation on plant leaves generally limit their growth by suppressing the gas diffusion in the leaf boundary-layer thereby decreasing photosynthetic and transpiration rates. Thus, the optimization of a CELSS will require the control of the airflow and concomitant gas/liquid transfer at the plant surfaces. The experimental and theoretical modeling of CELSS requires a comprehensive understanding of the micro to the macro levels of liquid gas phase transfer. Hence, an experimental set-up was developed at 1-g to evaluate the mass transfer coefficients due to condensation of humid air on specific geometries in well controlled environmental conditions. The goal was to establish correlations between the fluxes of mass and heat, the relative humidity and the mean flow for the development of theoretical models based on local transfer coefficients. The experiments were performed at ambient temperature, with a relative humidity between 35-70% and for a velocity range of 1.0-3.0 m.s(-1), La condensation d’air humide sur des substrats solides peut se produire dans beaucoup d’applications et ce phénomène est reconnu comme un des problèmes les plus difficiles à traiter pour l’amélioration de la qualité de l’air dans un espace clos. L’étude présente a été motivée par l’étude du couplage entre la ventilation et la condensation à l’intérieur d’écosystèmes clos artificiels (CELSS, Controled Ecological Life Support Systems), puisque ce couplage joue un rôle important sur la croissance de plantes supérieures dans des serres et sur les conditions de vie dans des cabines spatiales habitées, particulièrement pour les vols de longue durée ou les futures bases spatiales. Il est bien connu que l’augmentation des échanges gazeux au niveau des feuilles et la croissance des plantes dépendent des conditions organoleptiques et/ou des facteurs thermo-physiques environnants. Une convection insuffisante autour des plantes et de la condensation sur les feuilles limitent la croissance en supprimant la diffusion de gaz dans la couche limite de la feuille diminuant ainsi les taux de photosynthèse et de transpiration. Ainsi, l’optimisation d’un CELSS ne nécessitera le contrôle du flux d’air et du transfert gaz/liquide concomitant aux interfaces des plantes. Les modes expérimentaux et théoriques de CELSS exigent une compréhension complète des transferts gaz/liquide de l’échelle microscopique à l’échelle macroscopique. Un dispositif expérimental a été développé en gravité terrestre pour évaluer les coefficients de transfert de matière pour la condensation d’air humide sur des géométries spécifiques dans des conditions environnementales contrôlées précisément. Le but était d’établir des corrélations entre les flux de matière et de chaleur, l’humidité relative et l’écoulement moyen pour le développement de modèles théoriques basés sur des coefficients de transfert locaux. Les expériences ont été exécutées à température ambiante, avec une humidité relative comprise entre 35 et 70 % et pour une gamme de vitesse de 1,0 a 3,0 m.s

SSCI-VIDE+ING+CDA:YSC:DFA; International audience; Molecular simulation is used to unravel the adsorption mechanisms of xenon on Ag-doped ZSM-5 zeolite. We show that silver nanoparticles, which form at the external surface of zeolite crystallites, are responsible for enhanced xenon physisorption at very low pressure. We also propose a simple model of adsorption on such composite materials made up of silver-exchanged zeolites and silver nanoparticles adsorbed at the zeolite surface. This model, which allows predicting the adsorption of other gases without any additional parameters, provides a tool to characterize the amount of reduced silver as well as the silver particle size distribution (in good agreement with transmission electron microscopy images). The presence of a majority of silver nanoparticles is further characterized by means of X-ray diffraction and X-ray Absorption Spectroscopy at the silver K edge.

The paper deals with numerical prediction of laminar, transitional and turbulent regimes in confined flow between rotating and stationary discs. For the laminar and transitional flows, a spectral tau-Chebyshev method associated with a multistep time scheme is used. This approach allows accurate prediction of the two laminar regimes mentioned by Daily and Nece (1960) in their experimental studies. For the geometry under consideration (1/11 aspect ratio), the transition to unsteady motion occurs abruptly without any oscillatory behavior. Thus, the instabilities develop in a region localized near the external shroud, primarily along the stator side, according with experimental findings. For calculating turbulent flow regimes, one point second-order transport modeling has been implemented in a finite volume code. The superiority of advanced Reynolds stress transport models over the classical k−e model is decisive for predicting such a complex flow. This is particularly important in order to get a precise delineation of the adjacent turbulent and relaminarized regions within the cavity. This level of closure was crucial to produce numerical results in good agreement with experimental data.

(127)Xe has a longer half-life than (131m)Xe, it can be easily purely produced and it is present in the environment at very low level. For these reasons, (127)Xe is supposed to be a convenient quality control radionuclide for remote noble gas stations of the International Monitoring System (IMS) network. As CEA/DAM has recently developed two new photon/electron setups for low-level detection of (131m)Xe, (133m)Xe, (133)Xe and (135)Xe, we took the opportunity to test these setups for the measurement of a (127)Xe standard. The results and a detailed description of these measurements are presented in this paper. They illustrate the complexity of (127)Xe decay, emitting simultaneously several γ, X-rays, conversion electrons and Auger electrons; this results in highly summated coincidence spectra. The measurements performed provide precise electron energy calibration of the setups. The count rate of electrons in coincidence with iodine Kα X-rays was found to be surprisingly low, leading to the study of electron-gated photon spectrum. Finally, a comparison of three photon/electron coincidence spectra obtained with three different setups is given. The use of (127)Xe as a standard for energy calibration of IMS noble gas station is possible, but it appears to be quite complicated for efficiency check of noble gas station equipped with β/γ detectors.

The present work proposes a coupling between the hybrid lattice Boltzmann, the finite difference method, and the discrete ordinates method to simulate combined double diffusive convection and volumetric radiation in a square cavity filled with an emitting and absorbing gray gas. The vertical walls are kept at different temperatures and pollutant concentrations, while the horizontal walls are insulated and impermeable. A parametric study is carried out to evaluate the influence of control parameters such as the Lewis number (Le), Planck number (Pl), and reference temperature ratio (Θ0) on the flow field as well as on heat and mass transfer. The results are presented in terms of isotherms, streamlines, isoconcentrations, average Nusselt, and Sherwood numbers. They show that the volumetric radiation accelerates the flow and significantly alters the structure of the dynamic, concentration, and temperature fields, especially when the thermal forces are dominant. On the other hand, when the mass forces are dominant, the flow is slowed down. The influence of radiation is greater on the thermal field than on the dynamic and concentration fields.

The combined effects of thermocapillary and buoyancy forces in an open cavity heated from one side have been modeled numerically. The configuration is that of two shallow, immiscible superposed liquid layers. High Prandtl number fluids are considered under both 1- and μ- g environments. The interfaces are considered deformable. It is shown that encapsulation strongly reduces the flow in the lower layer, and that a γ-g environment significantly reduces the flow in the lower layer. The sensitivity of the flow structure to some physical properties is also described, and particularly the relevance of the thermocapillary forces.

The development of life support artificial environments for crews and plants for long duration space flights is a challenge today. The concept of bio-regenerative life support system (BLSS) imitates a simplified natural environment. Experimental or theoretical modeling of BLSS requires a thorough understanding of natural activities from micro to macro scales, like with plant culture for food production, or CO2/O2 conversion … Moreover, life support in space relies on both the amount of food and atmospheric O2 produced by plants in a confined space. It is well known that, the enhancement of the gas exchange with leaves and the growth of plants are dependent on the organoleptic and the surrounding thermo-physical factors. Insufficient air movement around plants and/or condensation on plant leaves generally limit their growth by decreasing photosynthetic and transpiration rates. Thus, the optimization of a BLSS will require controlling the airflow and coupled gas/liquid transfer at the plant surfaces. Hence, we have developed an experimental setup at 1-g to study the hydrodynamics and the condensation mass flux on specific geometries in controlled environmental conditions. An air-conditioned closed circuit wind tunnel was used to generate a flow of controlled temperature, hygrometry and hydrodynamics. Condensation of humid air on a small size horizontal flat plate was investigated. The temperature of the active surface is controlled and maintained below the dewpoint to induce condensation. The experiments were performed at ambient temperature, with a relative humidity between 35-70% and for a velocity range of 1.0-3.0 m.s -1 . The results lead to the evaluation of the local mass transfer coefficients in various conditions. The goal of this study is to develop a theoretical model to predict condensation mass flux at interfaces to be used in a CFD approach related to a closed environment for space applications: planetary flights, lunar-Mars bases.

International audience

This paper reports on a combined experimental and numerical investigation of BGO Czochralski growth. Different stages of the growth process are investigated. The effect of varying the Grashof number and the rotation Reynolds number on the flow and temperature distribution in the melt is explored over a range of parameters. Some aspects resulting from a non-isothermal crucible and from different sizes of the crystal radius are discussed.

For the success of long-term space flights, and the establishment of permanent bases in space, a well controlled self sustained environment is required. In order to optimize a closedloop bio-regenerative life support system, it is necessary to control the hydrodynamics and the coupled heat and mass transfer, which develops in a space habitat concerned with humans and plants. Thus, we have proposed an experimental set up that can gives us accurate predictions of heat and mass transfer at interfaces. We intend to introduce later on the measured heat and mass transfer coefficients in a global theoretical model. More precisely, this study focuses on the condensation phenomena of humid air on specific and simple geometries. For that purpose we induce condensation on an active surface maintained isothermal, and measure the mass transfer. The experiments were carried out in a wind tunnel, where a low turbulent flow develops and the temperature and hygrometric distributions are also well controlled. We have already studied the velocity profiles on vertical and horizontal flat plates with and without condensation. Velocity profiles within the boundary layer have already been discussed in dry conditions.

This paper concerns the prediction and the analysis of the steady and time‐dependent flow regimes that develop in liquid‐encapsulated Czochralski (LEC) systems for material processing. The combined effects of temperature gradient and rotation on the flow and the temperature field, and especially the influence of the encapsulant layer (of Prandtl number 10≤Pre≤3270 ) on the melt (Prm=0.015), are investigated using axisymmetric modeling. The accuracy of the solutions based on a finite element method is discussed. The effects of the Grashof number (up to Gr=1.9×107 ) and of the rotation Reynolds numbers of the crystal (up to ‖Res‖=104 ) and of the crucible (up to Rec=1.5×104) are analyzed.

In preparation for verification of the Comprehensive Nuclear-Test-Ban-Treaty, automated radioxenon monitoring is performed in two distinctive environments: Ottawa and Tahiti. These sites are monitored with SPALAX (Systeme de Prelevement d'air Automatique en Ligne avec l'Analyse des radioXenons) technology, which automatically extracts radioxenon from the atmosphere and measures the activity concentrations of 131m,133m,133,135Xe. The resulting isotopic concentrations can be useful to discern nuclear explosions from nuclear industry xenon emissions. Ambient radon background, which may adversely impact analyser sensitivity, is discussed. Upper concentration limits are reported for the apparently radioxenon free Tahiti environment. Ottawa has a complex radioxenon background due to proximity to nuclear reactors and medical isotope facilities. Meteorological models suggest that, depending on the wind direction, the radioxenon detected in Ottawa can be characteristic of the normal radioxenon background in the Eastern United States, Europe, and Japan or distinctive due to medical isotope production.