Effect of spray cooling on heat transfer in a two-phase helium flow

International audienceIn this paper, we describe an experimental study of the phenomenon of spray cooling in the case of liquid helium, either normal or superfluid, and its relationship to the heat transfer between an atomized diphasic flow contained in a long pipe, and the pipe walls. This situation is discussed in the context of the cooling of the superconducting magnets of the Large Hadron Collider (LHC). Experiments were conducted in a test loop reproducing the LHC cooling system, in which the vapor velocity and temperature could be varied in a large range. Shear induced atomization results in the generation of a droplet mist which was characterized by optical means. The thin liquid film deposited on the walls by the mist was measured using interdigitated capacitors. The cooling power of the mist was measured using thermal probes, and correlated to the local mist density. Analysis of the results shows that superfluidity has only a limited influence on both the film thickness and the mist cooling power. Using a simple model, we show that the phenomenon of spray cooling accounts for the measured non linearity of the global heat transfer. Finally, we discuss the relevance of our results for cooling the final focus magnets (inner triplets) in an upgraded version of the LHC

Thermo-hydraulique d'un écoulement horizontal d'hélium superfluide diphasique.

This study aims to characterise helium two-phase flows, and to identify the dependance of their characteristics on various thermo-hydraulic parameters : vapour velocity, liquid height, vapour density, specificities of superfluidity. Both the engineer and the physicist's points of view are taken into consideration : the first one in terms of optimisation of a particular cooling scheme based on a two-phase flow, and the second one in terms of more fondamental atomisation-related questions.Ce travail concerne l'étude thermohydraulique d'un écoulement d'hélium superfluide diphasique en conduite horizontale, comparable à celui mis en œuvre dans le refroidissement des aimants supraconducteurs du LHC au Cern. On montre que pour des vitesses de vapeur de quelques 3 à 4 m.s\mun, la phase liquide initialement stratifiée subit une atomisation qui se traduit par la présence d'un brouillard de gouttelettes transporté par la phase vapeur. Ceci a pu être montré en hélium superfluide comme en hélium normal sans différence majeure sur l'atomisation. Grâce à différents instruments et dispositifs de visualisation, plusieurs corrélations ont pu être mesurées entre la fraction de gouttelettes entraînées et la capacité frigorifique de l'écoulement diphasique, et ceci en fonction de paramètres expérimentaux comme le niveau liquide, la vitesse de la vapeur, ou encore sa densité

Thermo-hydraulique d'un écoulement horizontal d'hélium superfluide diphasique

Ce travail concerne l'étude thermohydraulique d'un écoulement d'hélium superfluide diphasique en conduite horizontale, comparable à celui mis en œuvre dans le refroidissement des aimants supraconducteurs du LHC au Cern. On montre que pour des vitesses de vapeur de quelques 3 à 4 m.s\mun, la phase liquide initialement stratifiée subit une atomisation qui se traduit par la présence d'un brouillard de gouttelettes transporté par la phase vapeur. Ceci a pu être montré en hélium superfluide comme en hélium normal sans différence majeure sur l'atomisation. Grâce à différents instruments et dispositifs de visualisation, plusieurs corrélations ont pu être mesurées entre la fraction de gouttelettes entraînées et la capacité frigorifique de l'écoulement diphasique, et ceci en fonction de paramètres expérimentaux comme le niveau liquide, la vitesse de la vapeur, ou encore sa densité.This study aims to characterise helium two-phase flows, and to identify the dependance of their characteristics on various thermo-hydraulic parameters : vapour velocity, liquid height, vapour density, specificities of superfluidity. Both the engineer and the physicist's points of view are taken into consideration : the first one in terms of optimisation of a particular cooling scheme based on a two-phase flow, and the second one in terms of more fondamental atomisation-related questions.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Tutorial Mismatches: Investigating the Frictions due to Interface Differences when Following Software Video Tutorials

International audienceVideo tutorials are the main medium to learn novel software skills. However, the User Interface (UI) presented in a video tutorial may differ from the learner’s UI because of customizations or differences in software versions. We investigate the frictions resulting from such differences on a learners’ ability to reproduce a task demonstrated in a video tutorial. Through a morphological analysis, we first identify 13 types of "interface differences" that differ in terms of availability, reachability and spatial location of features in the interface. To better assess the frictions resulting from each of these differences, we then conduct a laboratory study with 26 participants instructed to reproduce a vector graphics editing task. Our results highlight interesting UI comparison behaviors, and illustrate various approaches employed to visually locate features

Tutorial Mismatches: Investigating the Frictions due to Interface Differences when Following Software Video Tutorials

International audienceVideo tutorials are the main medium to learn novel software skills. However, the User Interface (UI) presented in a video tutorial may differ from the learner’s UI because of customizations or differences in software versions. We investigate the frictions resulting from such differences on a learners’ ability to reproduce a task demonstrated in a video tutorial. Through a morphological analysis, we first identify 13 types of "interface differences" that differ in terms of availability, reachability and spatial location of features in the interface. To better assess the frictions resulting from each of these differences, we then conduct a laboratory study with 26 participants instructed to reproduce a vector graphics editing task. Our results highlight interesting UI comparison behaviors, and illustrate various approaches employed to visually locate features

Characterization of a fungal procyanidin-degrading dioxygenase

International audienc

Characterization of a fungal procyanidin-degrading dioxygenase

International audienc

Biotransformation of procyanidins by a purified fungal dioxygenase : identification and characterization of the products using mass spectrometry

International audienceProcyanidins commonly known as condensed tannins are a type of polyphenol with wide abundance naturally. They are commonly known as potent anti-oxidants with powerful free radical scavenging activity as well as anti-tumor-promoting activity. Little is known about the enzymatic mechanisms/pathways involved in the microbial biotransformation of these polyphenolic molecules. The extracellular enzyme, dioxygenase produced by Aspergillus fumigatus was used as in vitro tools to study the degradation pathway of a model procyanidin dimer, namely procyanidin B2. The enzyme was purified to homogeneity by a two step process of anion-exchange chromatography coupled with FPLC followed by gel-filtration chromatography coupled with HPLC and the molecular mass estimated. In addition, the different biotransformed products resulted from the dioxygenase action on PB2 were purified using Reversed-Phase-High Performance Liquid Chromatography prior to their identification and characterization by structural elucidation using Electrospray Ionization-Mass Spectrometry. Subsequently, the mechanism of dioxygenase action on procyanidin dimer was defined

On the design of capacitive sensors using flexible electrodes for multipurpose measurements

International audienceThis article evaluates the potential of capacitive measurements using flexible electrodes to access various physical quantities. These electrodes are made of a thin metallic film, typical thickness 0.2 m, evaporated on a plastic substrate. Their large flexibility enables them to be mounted in complex geometries such as curved surfaces. In the configuration of planar condensers, using a very sensitive commercial capacitive bridge and a three-terminal measurement method, several measurements are presented. A relative resolution of 10 −8 for the thermal expansion of samples is obtained at low temperature in a differential configuration. The same technique adopted for pressure gauge measurements at low temperature led to a typical 0.1 Pa resolution over a dynamic range of 10 4 Pa. In the configuration of interleaved electrodes, condensers have been used to measure wetting by either bulk liquid helium or by thin continuous helium films in a cylindrical pipe. Both experimental and numerical evidence is provided, showing that the close proximity of a reference ground potential significantly increases the relative sensitivity to fluid wetting. Further, interleaved electrodes can be used to access both the area that is covered by a liquid film but also to determine the thickness of this film, provided it is comparable to the periodicity of the electrode pattern