References of "Caps, Hervé"
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See detailStudy of buoyancy driven heat transport in silicone oils and in liquid nitrogen in view of cooling applications
Satpathy, Kamalakanta ULiege; Duchesne, Alexis; Dubois, Charles et al

in International Journal of Heat & Mass Transfer (2018), 118

Motivated by applications for cooling superconducting pellets with liquid nitrogen, we consider a source with a fixed heating rate per unit volume, immersed in a liquid pool and cooled through natural ... [more ▼]

Motivated by applications for cooling superconducting pellets with liquid nitrogen, we consider a source with a fixed heating rate per unit volume, immersed in a liquid pool and cooled through natural convection. In one recent experimental investigation (Dubois et al., 2016) carried on silicone oils and liquid nitrogen, we have demonstrated that the velocity field satisfies specific scaling laws with respect to the temperature increase in the liquid pool. In this work, we pursue the analysis by modeling the heat transfer in a parallelepiped enclosure for a steady laminar flow regime. The Navier-Stokes equations are solved using a finite volume approach to obtain the detailed three-dimensional flow and heat transfer characteristics. A quantitative analysis of the velocity field over the temperature field shows that the experimental power laws are reproduced in simulations. Following Dubois and Berge (1978), a theoretical law originally introduced in the context of the classical Rayleigh-Bénard experiment is shown to be satisfied in the simulations over a wide range of Rayleigh numbers (Ra), assuming the definition of the characteristic convection length is adapted to the investigated geometry. Moreover, the simulations are shown to correctly reproduce the main features of the flow, including the characteristic convection length, for different heater lengths. [less ▲]

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See detailStudies on convective cooling of cryogenic fluids towards superconducting applications
Satpathy, Kamalakanta ULiege; Dubois, Charles; Duchesne, Alexis et al

in WIT Transactions on Engineering Sciences (2017), 118

To understand the cooling aspect through natural convection in a cryogenic fluid interacting with a constant heat source, numerical simulations are carried out in a parallelepiped enclosure. The 3D form ... [more ▼]

To understand the cooling aspect through natural convection in a cryogenic fluid interacting with a constant heat source, numerical simulations are carried out in a parallelepiped enclosure. The 3D form of N-S equations is solved to obtain the detailed flow features through path line profiles, isotherm contours and velocity vectors. The effect of heater aspect ratio (x/L) on the rate of heat transfer is studied in terms of the average Nusselt number (Nuave). The results indicate that effective heat transfer enhancement occurs for a small heater length, resulting in an efficient cooling. Increasing the heater length will favor heat transfer through conduction over convection. The maximum temperature difference across the fluid and the velocity magnitude are found to decrease with heater length. 3D and 2D results are in agreement for short heater lengths, but vary for higher heater lengths, presumably due to the essential effect of the heater width. Further analysis on different types of coolant reveals a constant correlation between Nuave and the Rayleigh number (Ra), with Nuave ~ Ra^0.374. Benchmark validation for natural convection in a square enclosure is found to be satisfactory against the reported results. [less ▲]

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See detailDeformations of soap bubbles in a uniform electric field
Mawet, Sébastien ULiege; Caps, Hervé ULiege; Dorbolo, Stéphane ULiege

Poster (2017, June 09)

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See detailDeformations of soap bubbles in a uniform electric field
Mawet, Sébastien ULiege; Caps, Hervé ULiege; Dorbolo, Stéphane ULiege

Conference (2017, March 15)

The study of the deformations undergone by a soap bubble submitted to an electrical force began with Taylor and Wilson 1 and the observation of the so-called Taylor’s cones. Beyond this particular ... [more ▼]

The study of the deformations undergone by a soap bubble submitted to an electrical force began with Taylor and Wilson 1 and the observation of the so-called Taylor’s cones. Beyond this particular structure, few studies analyzed the bubble deformations. For example, what is the link between the deformations and the electrical force ? Or, how do charges move in the thin soap film formed by the bubble ? To answer those questions, we characterize the shape variations of the surface of the bubble immersed in the uniform electric field of a plan capacitor. In particular, our study focuses on hemispherical bubbles lying on the bottom electrode of a plane capacitor. This study allows us to observe some interesting phenomena like the appearance of a hysteresis cycle in the deformation amplitude. [less ▲]

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See detailElectrically charged droplets in microgravity
brandenbourger, martin; Caps, Hervé ULiege; vitry, youen et al

in Microgravity Science and Technology (2017)

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See detailBehaviour of bulk superconducting trapped field magnets subjected to magnetic fields with a transverse component
Vanderbemden, Philippe ULiege; Caps, Hervé ULiege; Vanderheyden, Benoît ULiege et al

Conference (2016, November 10)

Bulk superconductors can be used as trapped field magnets with unprecedented performances. Such trapped field magnets find a variety of engineering applications, in particular for brushless rotating ... [more ▼]

Bulk superconductors can be used as trapped field magnets with unprecedented performances. Such trapped field magnets find a variety of engineering applications, in particular for brushless rotating machines and levitation devices. Compared to conventional permanent magnets, however, the magnetic field generated by a superconducting trapped field magnet is much more sensitive to the presence of an external field that is not perfectly aligned with the superconductor magnetic moment, i.e. when the external field has a transverse component. A situation where the superconductor experiences a magnetic field with a transverse component is likely to happen several times during running operation of the device. As an example, in a “trapped flux” synchronous machine, any variation of the load of the shaft may lead to a slight misalignment of the magnetic moment of the superconductor (placed in the rotor) with respect to the rotating field (generated by the stator). In such a situation, the superconductor is subjected to a rotating field, and the situation is likely to be different from a situation where the superconductor is subjected to a pure transverse field. In the present work, we aim at examining different scenarios (i.e. transverse or rotating) where the trapped field magnet is subjected to a transverse component. These configurations are examined both experimentally and numerically. The numerical model is used to determine the distribution of currents in the cross-section of the superconductor. We examine the conditions where the rotating field leads to a partial remagnetization of the sample and is therefore less detrimental that the application of a pure transverse field. We also show that the magnetic moment of the sample may behave differently that the field at the surface of the superconductor. Finally, we investigate the behavior of structures where the superconductor is attached to a thin ferromagnetic disk, and show the beneficial effect of such hybrid structures compared to the superconductor alone. Acknowledgements : The research was funded through the University of Liège (ULg) and an ARC grant for Concerted Research Actions, financed by the French Community of Belgium (Wallonia-Brussels Federation), under reference ARC 11/16-03. We greatly acknowledge M. Morita, S. Nariki and H. Teshima from Nippon Steel & Sumitomo Metal Corporation, Futtsu, Chiba. [less ▲]

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See detailBetween inertia and viscous effects: Sliding bubbles beneath an inclined plane
dubois, charles; duchesne, alexis; Caps, Hervé ULiege

in europhysics letters (2016), 115

The ascent motion of an air bubble beneath an inclined plane is experimentally studied. The effects of the surrounding liquid viscosity and surface tension, the bubble radius and the tilt angle are ... [more ▼]

The ascent motion of an air bubble beneath an inclined plane is experimentally studied. The effects of the surrounding liquid viscosity and surface tension, the bubble radius and the tilt angle are investigated. A dynamical model is proposed. It opposes the buoyant driving force to the hydrodynamical pressure arising from the bubble motion and the capillary meniscus generated in front of the bubble in order to create a lubrication film between the bubble and the plate. This model is compared to experimental data and discussed. [less ▲]

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See detailSuperconductors used as trapped field magnets : investigation of hybrid structures combining superconducting and ferromagnetic materials
Vanderbemden, Philippe ULiege; Fagnard, Jean-François ULiege; Caps, Hervé ULiege et al

Conference (2016, August 30)

In addition to their unique ability to carry electric currents without loss, superconductors are able to trap significant magnetic flux densities at low temperature. In so-called type-II irreversible ... [more ▼]

In addition to their unique ability to carry electric currents without loss, superconductors are able to trap significant magnetic flux densities at low temperature. In so-called type-II irreversible superconductors, these properties are due to the pinning of individual flux lines (vortices) by defects at the nanoscale level. In this talk the influence of pinning on the magnetic properties of bulk superconductors will be explained and illustrated, with the emphasis placed on how pinning can be exploited to produce “trapped field magnets” for practical applications. We will then show how the properties of these trapped field magnets are enhanced when superconductors (SC) are combined to soft ferromagnetic (FM) alloys [1,2]. In particular we investigate the properties of macroscopic FM/SC/FM structures where the superconductor is sandwiched between two ferromagnetic sections, one of each circular face. In particular we show how the properties of the whole structure is influenced by the saturation magnetization and the geometry of the ferromagnetic material. References: 1. M P Philippe, J-F Fagnard, S Kirsch, Z Xu, A R Dennis, Y H Shi, D A Cardwell, B Vanderheyden, and P Vanderbemden, Magnetic characterisation of large grain, bulk Y–Ba–Cu–O superconductor–soft ferromagnetic alloy hybrid structures. Physica C: 502 (2014) 20-30. 2. M P Philippe, M D Ainslie, L Wera, J-F Fagnard, A R Dennis, Y H Shi, D A Cardwell, B Vanderheyden, and P Vanderbemden, Influence of soft ferromagnetic sections on the magnetic flux density profile of a large grain, bulk Y–Ba–Cu–O superconductor. Superconductor Science and Technology: 28 (2015) 095008. [less ▲]

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See detailStudies of heat transport in cryogenic fluids toward superconducting applications
Satpathy, Kamalakanta ULiege; Dubois, Charles; Fagnard, Jean-François ULiege et al

Poster (2016, June 16)

To meet the increasing global energy demand with minimal green house effect, electrical energy is a viable option. But, it requires an efficient electrical power system with optimal loss. Towards this ... [more ▼]

To meet the increasing global energy demand with minimal green house effect, electrical energy is a viable option. But, it requires an efficient electrical power system with optimal loss. Towards this, superconducting materials represent a promising way of improving the existing systems. However, the efficiency may be affected by a small temperature increase due to electromagnetic losses induced by time-varying magnetic fields. To minimize this, two approaches can be considered (i) reduce the losses and (ii) improve the heat exchange with the cooling environment. Although experimental and theoretical studies of the superconducting losses have been extensively pursued [1], few attempts have been made to combine the 'losses' and the 'cooling' aspects in the current scenario. Such studies require a detailed characterization of magneto-thermal interaction of the superconductors, as well as fundamental aspects of heat draining by the cryogenic fluid. Towards this, numerical studies on natural convection in an enclosed cavity, interacting with a constant heat source (heater) are carried out to understand the cooling efficiency of the cryogenic fluids (viz., liquid nitrogen, silicon oil and water). Natural convection heat transfer in an enclosure continues to be an active research area, due to its significance for both fundamental interests and engineering applications. Majority of the published studies can be classified into two groups: enclosure heated from below and cooled from above (Rayleigh–Bénard problem) and differentially heated enclosures [2]. Considerable attention has been given to natural convection from vertical/horizontal enclosures specified either with constant temperature or heat flux, while limited studies has been done with constant volumetric heat source [3]. The resulting characteristics of fluid flow and heat transfer are quite interesting and deserve a detailed investigation, which motivates for the present work. As a priori, three dimensional steady forms of incompressible Navier-Stokes equations are solved through finite volume approach [4]. Detailed flow features are presented in terms of velocity, temperature and path line profiles for different heater lengths. Comparative analyses are further reinforced in terms of average Nusselt number (Nu) for different fluids. It shows that, effective heat transfer enhancement occurs for liquid nitrogen with the shortest heater length, resulting in an efficient cooling. The profile of temperature and velocity magnitude distributions agrees well with the in-house experiment. Benchmark validation is found to be satisfactorily against the reported result [5]. Complete descriptions on geometrical details, governing equations, boundary conditions and solution methodology adopted for the numerical solution will be provided in full length paper. This study will be a gateway for further magneto-thermal analysis in an electromagnetic environment. [less ▲]

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See detailBulles de savon dans un champ électrique uniforme
Mawet, Sébastien ULiege; Hardouin, Jérôme; Caps, Hervé ULiege

Conference (2016, January 28)

L'étude des déformations subies par une bulle lors de sa charge a commencé avec Taylor et Wilson et l'observation des cônes de Taylor. Au-delà de ces structures particulières, les déformations en elles ... [more ▼]

L'étude des déformations subies par une bulle lors de sa charge a commencé avec Taylor et Wilson et l'observation des cônes de Taylor. Au-delà de ces structures particulières, les déformations en elles-mêmes n'ont été que peu analysées. L'objectif premier de ce travail est de caractériser les changements de la surface de la bulle lorsque celle-ci est placée dans un condensateur plan et soumise à un champ électrique uniforme. Cette étude nous a permis notamment de mettre en évidence l'apparition d'un cycle d'hystérèse dans l'amplitude des déformations. [less ▲]

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See detailTightrope dancer bubbles
Duchesne, Alexis ULiege; Caps, Hervé ULiege; Dubois, charles

in Physical Review Fluids (2016), 1(5), 050504

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See detailElectrically charged droplets in microgravity
Caps, Hervé ULiege; brandenbourger, martin; vitry, youen et al

Conference (2016)

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See detailFoams in a rotating drum
Caps, Hervé ULiege; bronfort, arianne

Conference (2016)

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See detail2D foams in a rotating drum
Caps, Hervé ULiege; bronfort, arianne

Conference (2016)

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See detailSliding bubbles on a hot horizontal wire in a subcooled bath
duchesne, alexis; dubois, charles; Caps, Hervé ULiege

Conference (2016)

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See detailLa danse des Funam-Bulles : promenades de bulles sur un fil chaud immerge dans un bain.
Duchesne, Alexis; Dubois, Charles; Caps, Hervé ULiege

in compte-rendu (2016)

Lorsque l’on chauffe un fil resistif horizontal dans un bain liquide et que l’on d ́epasse localement la temp ́erature d’ ́ebullition dudit liquide, des bulles de vapeur vont nucl ́eer a` la surface du ... [more ▼]

Lorsque l’on chauffe un fil resistif horizontal dans un bain liquide et que l’on d ́epasse localement la temp ́erature d’ ́ebullition dudit liquide, des bulles de vapeur vont nucl ́eer a` la surface du fil. Les diff ́erentes th ́eories pr ́esentes dans la litt ́erature pr ́edisent que les bulles g ́en ́er ́ees depuis des sites de nucl ́eation actifs vont grandir puis quitter la surface chauffante en raison des forces d’inertie et de la pouss ́ee d’Archim`ede. N ́eanmoins, on observe ici un comportement diff ́erent : les bulles glissent le long du fil chaud. Dans cette situation, des ́etats inattendus ont pu ˆetre observ ́es, allant de la simple translation a` la formation d’amas de bulles. Nous avons ́egalement remarqu ́e que les bulles pouvaient brusquement changer de sens de d ́eplacement sur le fil et interagir. Enfin, nous proposons une interpr ́etation des ph ́enom`enes de maintien de la bulle sur le fil et de d ́eplacement de la bulle en terme d’effets Marangoni. [less ▲]

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See detailMagnetic moment and local magnetic induction of superconducting/ferromagnetic structures subjected to crossed fields: experiments on GdBCO and modelling
Fagnard, Jean-François ULiege; Morita, Mitsuru; Nariki, Shinya et al

in Superconductor Science and Technology (2016), 29(12), 125004

Recent studies have shown that ferromagnetic materials can be used together with bulk high temperature superconductors in order to improve their magnetic trapped field. Remarkably, it has also been ... [more ▼]

Recent studies have shown that ferromagnetic materials can be used together with bulk high temperature superconductors in order to improve their magnetic trapped field. Remarkably, it has also been pointed out that ferromagnets can help in reducing the crossed field effect, namely the magnetization decay that is observed under the application of AC transverse magnetic fields. In this work, we pursue a detailed study of the influence of the geometry of the ferromagnetic part on both trapped fields and crossed field effects. The magnetic properties of the hybrid superconducting/soft ferromagnetic structures are characterized by measuring the magnetic moment with a bespoke magnetometer and the local magnetic field density with Hall probes. The results are interpreted by means of 2D and 3D numerical models yielding the distribution of the superconducting currents as a function of the ferromagnet geometry. We examine in details the distortion of the shielding superconducting currents distribution in hybrid structures subjected to crossed magnetic fields. These results confirm the existence of an optimum thickness of the ferromagnet, which depends on the saturation magnetization of the ferromagnetic material and the current density of the superconductor. A hybrid structure providing an efficient protection against the crossed magnetic field while maintaining the magnetic induction along the axis of the structure is suggested. The limitations of the 2D modelling in this configuration are discussed. [less ▲]

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See detailInfluence of crossed fields in structures combining large grain, bulk (RE)BCO superconductors and soft ferromagnetic discs
Philippe, Matthieu ULiege; Fagnard, Jean-François ULiege; Wera, Laurent ULiege et al

in Journal of Physics: Conference Series (2016), 695

Bulk (RE)BCO superconductors are able to trap record magnetic fields and can be used as powerful permanent magnets in various engineering applications such as rotating machines and magnetic bearings. When ... [more ▼]

Bulk (RE)BCO superconductors are able to trap record magnetic fields and can be used as powerful permanent magnets in various engineering applications such as rotating machines and magnetic bearings. When such superconducting (SC) “trapped field magnets” are combined to a ferromagnetic (FM) disc, the total magnetic moment is increased with respect to that of the superconductor alone. In the present work, we study experimentally the magnetic behaviour of such hybrid FM/SC structures when they are subjected to cycles of applied field that are orthogonal to their permanent magnetization, i.e. a “crossed-field” configuration. Experimental results show that the usual “crossed-field demagnetization” caused by the cycles of transverse field is strongly reduced in the presence of the ferromagnet. [less ▲]

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See detailRotation of melting ice disks due to melt fluid flow
Dorbolo, Stéphane ULiege; adami, nicolas; Dubois, Charles ULiege et al

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2016)

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See detailResonant and antiresonant bouncing droplets
Hubert, Maxime ULiege; Robert, Damien; Caps, Hervé ULiege et al

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2015), 91

When placed onto a vibrating liquid bath, a droplet may adopt a permanent bouncing behavior, depending on both the forcing frequency and the forcing amplitude. The relationship between the droplet ... [more ▼]

When placed onto a vibrating liquid bath, a droplet may adopt a permanent bouncing behavior, depending on both the forcing frequency and the forcing amplitude. The relationship between the droplet deformations and the bouncing mechanism is studied experimentally and theoretically through an asymmetric and dissipative bouncing spring model. Antiresonance phenomena are evidenced. Experiments and theoretical predictions show that both resonance at specific frequencies and antiresonance at Rayleigh frequencies play crucial roles in the bouncing mechanism. In particular, we show that they could be exploited for bouncing droplet size selection. [less ▲]

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