Numerical and experimental studies of the flow around a partially submerged vertical cylinder

International audienceL'écoulement et l'injection d'air autour d'un cylindre vertical partiellement immergé, en translation, est étudié expérimentalement et numériquement. Le régime d'écoulement est turbulent avec 15 000 < Re < 60 000 et 0.4 < F r < 1.7, où Re et F r sont les nombres de Reynolds et de Froude adimensionnés à l'aide du diamètre D du cylindre. Une cavité à l'aval du cylindre est observée. L'objectif de ce travail est d'étudier les efforts de traînée, l'élévation de la surface libre et la vitesse critique à partir de laquelle il y a entraînement d'air. Un bon accord entre les expériences et les simulations a été trouvé, évaluant ainsi la profondeur de la cavité, le coefficient de traînée et la vitesse critique d'injection d'air. Abstract : The flow around a vertical cylinder piercing the free-surface is studied experimentally and numerically. The cylinder has a free-end and the range of velocities are in the regime of turbulent wake with experiments and simulations carried out for 15 000 < Re < 60 000 and 0.4 < F r < 1.7, where Re and F r are the Reynolds and Froude numbers based on the cylinder diameter D. A cavity downstream the cylinder is observed. The focus here is on drag force measurement, free-surface elevation, and critical velocity for air-entrainment. Specifically, a good agreement between experiments and simulations is obtained for the cavity depth, the drag coefficient and the critical velocity

Effect of Crystallographic Phase (β vs. γ) and Surface Area on Gas Phase Nitroarene Hydrogenation Over Mo2N and Au/Mo2N

The catalytic action of Mo2N and Au/Mo2N has been assessed in the selective gas phase hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN). The nitrides were synthesised via temperature programmed treatment of MoO3 in H2+N2 and Au introduced by deposition-precipitation with urea. We have examined the influence of nitride crystallographic phase (tetragonal β-Mo2N vs. cubic γ-Mo2N) and surface area (7-66m2g−1) on the catalytic response. Catalyst activation by temperature programmed reduction has been monitored and the reduced catalysts characterised in terms of BET area/pore volume, H2 chemisorption/temperature programmed desorption (TPD), powder X-ray diffraction (XRD), elemental analysis, scanning (SEM) and transmission (TEM) electron microscopy and X-ray photoelectron spectroscopy (XPS) measurements. The formation of β- and γ-Mo2N was confirmed by XRD and TEM. γ-Mo2N exhibits a platelet morphology whereas β-Mo2N is characterised by an aggregation of small crystallites. Hydrogen chemisorption and TPD analysis have established a greater hydrogen uptake capacity (per unit area) for β-Mo2N relative to γ-Mo2N, which is associated with surface nitrogen deficiency, i.e. higher surface Mo/N for β-Mo2N. Incorporation of Au on both nitrides resulted in an increase in surface hydrogen. The Au phase takes the form of nano-scale particles with a mean size of 7 and 4nm on β-Mo2N and γ-Mo2N, respectively. Both β-Mo2N and γ-Mo2N promoted the exclusive hydrogenation of p-CNB to p-CAN where the β-form delivered a higher specific (per m2) rate; the specific rate for γ-Mo2N was independent of surface area. The inclusion of Au on both nitrides served to enhance p-CAN productio

Radon Investigation in 650 Energy Efficient Dwellings in Western Switzerland: Impact of Energy Renovation and Building Characteristics

As part of more stringent energy targets in Switzerland, we witness the appearance of new green-certified dwellings while many existing dwellings have undergone energy efficiency measures. These measures have led to reduced energy consumption, but rarely consider their impact on indoor air quality. Consequently, such energy renovation actions can lead to an accumulation of radon in dwellings located in radon-prone areas at doses that can affect human health. This study compared the radon levels over 650 energy-efficient dwellings in western Switzerland between green-certified (Minergie) and energy-renovated dwellings, and analyzed the building characteristics responsible of this accumulation. We found that the newly green-certified dwellings had significantly lower radon level than energy-renovated, which were green- and nongreen-certified houses (geometric mean 52, 87, and 105 Bq/m3, respectively). The new dwellings with integrated mechanical ventilation exhibited lower radon concentrations. Thermal retrofitting of windows, roofs, exterior walls, and floors were associated with a higher radon level. Compared to radon measurements prior to energy renovation, we found a 20% increase in radon levels. The results highlight the need to consider indoor air quality when addressing energy savings to avoid compromising occupants’ health, and are useful for enhancing the ventilation design and energy renovation procedures in dwellings

Fungal Contaminants in Energy Efficient Dwellings: Impact of Ventilation Type and Level of Urbanization

: The presence of growing fungi in the indoor environment has been associated with the development of respiratory problems such as asthma or allergic rhinitis, as well as the worsening of respiratory pathologies. Their proliferation indoors could be a result of water leakage or inadequate ventilation. Although the factors promoting mould growth have been widely investigated in traditional dwellings, little work has been done in energy efficient dwellings. Here, the effectiveness of ventilation type, i.e., natural or mechanical, in influencing mould development was estimated in 44 recent and 105 retrofitted energy efficient dwellings. Fungi growing on surfaces were investigated in the dwellings situated in rural, peri-urban, and urban regions of Switzerland. The presence of these fungi was also investigated in bedroom settled dust. Information on building characteristics and owners’ lifestyle were collected. Significant associations were found with the level of urbanisation, the location of mouldy area in dwellings, and the diversity of fungal taxa. Dwellings in peri-urban zones showed the most frequent fungal contamination in the owners’ bedroom and the highest diversity of fungal genera among dwellings. While the urbanisation level or the ventilation type favoured no specific genus, we found marked disparities in the diversity of fungi growing on surfaces in naturally ventilated versus mechanically ventilated dwellings. Aspergillus, in particular, was a frequent surface contaminant in bedrooms with natural ventilation, but not in those mechanically ventilated. We observed a strong association between fungal growth on surfaces and the number of fungal particles counted in the settled dust of owners’ bedrooms. These results demonstrate the importance of ventilation systems in energy efficient dwellings in controlling fungal proliferation in living areas

Experiments and Simulations of Free-Surface Flow behind a Finite Height Rigid Vertical Cylinder

We present the results of a combined experimental and numerical study of the free-surface flow behind a finite height rigid vertical cylinder. The experiments measure the drag and the wake angle on cylinders of different diameters for a range of velocities corresponding to 30,000 &lt;Re&lt; 200,000 and 0.2&lt;Fr&lt;2 where the Reynolds and Froude numbers are based on the diameter. The three-dimensional large eddy simulations use a conservative level-set method for the air-water interface, thus predicting the pressure, the vorticity, the free-surface elevation and the onset of air entrainment. The deep flow looks like single phase turbulent flow past a cylinder, but close to the free-surface, the interaction between the wall, the free-surface and the flow is taking place, leading to a reduced cylinder drag and the appearance of V-shaped surface wave patterns. For large velocities, vortex shedding is suppressed in a layer region behind the cylinder below the free surface. The wave patterns mostly follow the capillary-gravity theory, which predicts the crest lines cusps. Interestingly, it also indicates the regions of strong elevation fluctuations and the location of air entrainment observed in the experiments. Overall, these new simulation results, drag, wake angle and onset of air entrainment, compare quantitatively with experiments

Future experimental programmes in the CROCUS reactor

CROCUS is a teaching and research zero-power reactor operated by the Laboratory for Reactor Physics and Systems Behaviour (LRS) at the Swiss Federal Institute of Technology (EPFL). Three new experimental programmes are scheduled for the forthcoming years. The first programme consists in an experimental investigation of mechanical noise induced by fuel rods vibrations. An in-core device has been designed for allowing the displacement of up to 18 uranium metal fuel rods in the core periphery. The vibration amplitude will be 6 mm in the radial direction (±3 mm around the central position), while the frequency can be tuned between 0.1 and 5 Hz. The experiments will be used to validate computational dynamic tools currently under development, which are based on DORT-TD and CASMO/S3K code systems. The second programme concerns the measurement of in-core neutron noise for axial void profile reconstruction. Simulations performed at Chalmers University have shown how the void fraction and velocity profiles can be reconstructed from noise measurements. The motivation of these experiments is to develop an experimental setup to validate in-core the method in partnership with Chalmers University. The third experimental programme aims at continuing the validation effort on the nuclear data required in the calculation of GEN-III PWR reactors with heavy steel reflectors. This is a collaboration with CEA Cadarache that extends the results of the PERLE experiments carried out in the E reactor at CEA. Scattering cross sections at around 1 MeV will be studied separately by replacing successively the water reflector by sheets of stainless steel alloy and pure metals – iron, nickel, and chromium. Data will be extracted from the measured flux attenuation using foils in the metal reflector and from the criticality effects of these reflectors. In parallel to the three reactor experiments, we develop in-core detectors and measurement systems. Following the last development of a neutron noise measurement station in pulse mode, a second neutron noise station in current mode is being designed. In current mode the reactor can be used at higher power without dead time effects. It allows faster measurement time or lower results uncertainties. Finally, a joint development of a full new detection system based on chemical vapour deposited (sCVD) diamond has been started with the CIVIDEC instrumentation start-up company. A first prototype has been tested in November 2015 in CROCUS. One of the main purposes is to work on the discrimination of gammas, thermal and fast neutrons for demonstrating the interest of this detector type in a mixed neutron-gamma field

Comment former des groupes d'étudiants homogènes à partir des résultats de SELF ?

International audienc

Introduction à l'hygiène du travail : un support de formation

[Table des matières] A. Cadre et contexte général : Place et démarche de santé au travail ; Place de l'hygiène du travail dans la santé au travail ; Approche pluridisciplinaire et équipe de santé au travail ; Interface avec d'autres acteurs ; Gestion du risque ; Concept général ; Les outils du management ; La notion de risque acceptable. - B. Hygiène et sécurité du travail : Définition et historique de l'hygiène du travail ; Défis et perspectives ; Ethique professionnelle ; Démarche de l'hygiène du travail ; Méthode d'analyse des risques. - C. Identification des dangers : Méthodes ; Etiquetage des produits chimiques. - D. Evaluation des risques : Généralités ; Stratégie ; Normes ; Risques chimiques ; Toxicologie ; Gaz, vapeurs ; Aérosols ; Amiante ; Surveillance biologique ; Laboratoires ; Risques physiques ; Le Bruit ; Les vibrations ; Les radiations ionisantes ; Rayonnement optique et lasers ; Radiofréquence et rayonnements de basse fréquence ; Le stress thermique ; Environnements hypo- et hyperbares ; les risques biologiques ; Facteurs généraux liés à l'ambiance ; Aspects ergonomiques ; Généralités ; Charge physique ; Organisation du travail ; Instruments de mesure. - E. Maîtrise du risque : Organisation de la prévention ; Un nouveau concept de gestion du risque ; Prévention technique ; A la source - substitution ; A l'interface - ventilation ; Sur la cible. Equipements de protection individuelle ; Au niveau du travailleur - Prévention médicale ; Information et formation des travailleurs