Experimental study of ultracold neutron production in pressurized superfluid helium

We have investigated experimentally the pressure dependence of the production of ultracold neutrons (UCN) in superfluid helium in the range from saturated vapor pressure to 20bar. A neutron velocity selector allowed the separation of underlying single-phonon and multiphonon pro- cesses by varying the incident cold neutron (CN) wavelength in the range from 3.5 to 10{\AA}. The predicted pressure dependence of UCN production derived from inelastic neutron scattering data was confirmed for the single-phonon excitation. For multiphonon based UCN production we found no significant dependence on pressure whereas calculations from inelastic neutron scattering data predict an increase of 43(6)% at 20bar relative to saturated vapor pressure. From our data we conclude that applying pressure to superfluid helium does not increase the overall UCN production rate at a typical CN guide.Comment: 18 pages, 8 figures Version accepted for publication in PR

Numerical Modeling of the Effects of Channel Configurations and Inclination Angles Inducing Buoyancy on Reverse Osmosis

This numerical study presents a comparison between two different reverse osmosis channel configurations. The physical properties were considered in the computational model as a function of the solute mass fraction. A critical comparison was performed between double-sided membrane channel and single-sided one considering the concentration and flow distribution. Gravitational effect was implemented by introducing the inclination of double membrane geometry for the first time in the literature of reverse osmosis systems. FORTRAN in-house code was developed to resolve conservation equations (mass, momentum, and solute mass fraction) based on the finite volume method. The results of the simulation show that the water recovery factor of double-membrane arrangement is two times higher than the single membrane arrangement. Concentration polarization (CP) can be reduced by both increasing the feed Reynolds number (Re) and decreasing the Aspect Ratio (AR). Considering the cases of low flow rates (up to Re = 40) with the flow orientation in the direction of gravity inducing buoyancy effects. The influence of the inclination showed that the average permeate flux, and the water recovery are proportional to the inclination angle up to the maximum values at the right angle (vertical plane)

Sessile Drop in Microgravity: Creation, Contact Angle and Interface

We present in this paper the results obtained from a parabolic flight campaign regarding the contact angle and the drop interface behavior of sessile drops created under terrestrial gravity (1g) or in microgravity (mu g). This is a preliminary study before further investigations on sessile drops evaporation under microgravity. In this study, drops are created by the mean of a syringe pump by injection through the substrate. The created drops are recorded using a video camera to extract the drops contact angles. Three fluids have been used in this study : de-ionized water, HFE-7100 and FC-72 and two heating surfaces: aluminum and PTFE. The results obtained evidence the feasibility of sessile drop creation in microgravity even for low surface tension liquids (below 15 mN m (-aEuro parts per thousand 1)) such as FC-72 and HFE-7100. We also evidence the contact angle behavior depending of the drop diameter and the gravity level. A second objective of this study is to analyze the drop interface shape in microgravity. The goal of the these experiments is to obtain reference data on the sessile drop behavior in microgravity for future experiments to be performed in an French-Chinese scientific instrument (IMPACHT)

A Common Framework Using Expected Types for Several Type Debugging Approaches

Many different approaches to type error debugging were developed independently. In this paper, we describe a new common framework for several type error debugging approaches. For this purpose, we introduce expected types from the outer context and propose a method for obtaining them. Using expected types, we develop three type error debugging approaches: enumeration of type error messages, type error slicing and (improved) interactive type error debugging. Based on our idea we implemented prototypes and confirm that the framework works well for type debugging

Characterization of interface properties of fluids by evaporation of a capillary bridge

International audienceThe surface properties between two non-miscible fluids are key elements to understand mass transfer, chemistry and bio-chemistry at interfaces. In this paper, surface properties are investigated in evaporating and non-evaporating conditions. A capillary bridge between two large plates (similar to a Hele-Shaw cell) is considered. The temporal evolution of surface forces and mass transfers due to evaporation of the liquid are measured. The force depends on surface properties of the substrate. It is adhesive in the wetting case and repulsive in the non-wetting case. The force is also shown to depend linearly on the volume of the capillary bridge F ∝ V 0 and inversely to the height of the bridge. Modelling is performed to characterize both surface force and evaporation properties of the capillary bridge. The evaporation is shown to be diffusion driven and is decoupled from the bridge mechanics

Etude expérimentale des écoulements darcéens à travers un lit de fibres rigides empilées aléatoirement : influence de la porosité

Experimental studies have been carried out on fluid flow through porous media made up of randomly packed monodisperse fibers. The fibers of fixed diameter have an aspect ratio ($L/d$) varying between 4 and 70 given porosities of the porous media varying between 0.35 and 0.90. The relationships between friction losses and superficial velocity have been systematically determined for each porous medium. A detailed analysis is carried out for low fluid velocities. The influence of flow direction on pressure drop is studied along two perpendicular directions: it is found that fibrous media behave globally in isotropic manner. The permeability and the Kozeny Carman parameter $k_{\rm k}$ are deduced from experimental results. The variations of the permeability increase exponentially with the porosity. The Kozeny Carman parameter $k_{\rm k}$ is a decreasing function of the porosity $\epsilon(L/d)$ and tends asymptotically to a value close to that deduced from a modified Ergun relation. The important decrease, observed for small aspect ratios, is certainly an effect of the cut sections of fibers. This effect becomes negligible for larger aspect ratios. The results in terms of permeability and of Kozeny Carman parameter $k_{\rm k}$ are systematically compared to those deduced from various theoretical models. Generally, these models consider cylinders arranged in simple network, the flow being either parallel or perpendicular to the axis of cylinders. The variation laws of the parameter $k_{\rm k}$, deduced from different models, present important discrepancies with our experimental results. The theoretical models, established for regular arrays of fibers do not correctly describe the behavior of randomly packed fibers.Des études expérimentales de l'écoulement d'un fluide à travers un milieu poreux constitué de fibres monodisperses empilées aléatoirement sont réalisées. Les milieux fibreux étudiés ont des porosités variant de 0,35 à 0,90. Ces porosités sont obtenues à l'aide de fibres dont le rapport d'aspect $L/d$ varie de 4 à 70. Les lois de perte de charge en fonction de la vitesse du fluide sont déterminées systématiquement pour chaque milieu poreux. Une analyse détaillée est effectuée pour les faibles vitesses d'écoulement. L'influence de la direction de l'écoulement sur les lois de perte de charge est étudiée. Celles-ci sont établies suivant deux directions perpendiculaires. Les résultats obtenus mettent en évidence un comportement du milieu fibreux globalement isotrope vis à vis de l'écoulement du fluide. La perméabilité et le paramètre de Kozeny Carman $k_{\rm k}$ sont déduits des résultats expérimentaux. Les variations de la perméabilité en fonction de la porosité suivent une loi de type exponentiel. Le paramètre de Kozeny Carman $k_{\rm k}$ décroît en fonction de la porosité $\epsilon(L/d)$ et tend asymptotiquement vers une valeur proche de celle déduite de la relation d'Ergun modifiée. La décroissance importante, observée pour les petits rapports d'aspect, est sans doute due aux effets induits par les surfaces de base des fibres. Ces effets deviennent négligeables pour les grands rapports d'aspect. Les résultats en terme de perméabilité et de paramètre de Kozeny Carman sont comparés systématiquement avec les modèles proposés dans la littérature. Généralement, ces modèles supposent des cylindres de grande longueur, disposés en réseaux simples. L'écoulement est soit parallèle, soit perpendiculaire à l'axe des cylindres. Les lois de variation du paramètre $k_{\rm k}$, déduites des différents modèles, présentent des écarts importants avec les résultats expérimentaux. Ces résultats semblent montrer qu'une disposition des fibres en réseaux simples ne permet pas une description convenable des écoulements à travers les empilements aléatoires de fibres