Modelling of a thermosiphon effect in a radiator

Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.Heat exchangers have multiple applications. We find them in domestic heating, solar heating systems and also in many cooling systems. Our paper is concerned with oil filled electric radiators. This work gives our conclusion concerning a change in design of one model and its consequences on the internal fluid circulation.vk201

Experimental and numerical investigation on the impact of nanoparticles in the development of thermosyphon

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.Addition of nanoparticles is a known way to modify the behavior of a fluid in terms of heat transfer. This fact reaches its limits when it comes to natural convection. The aim of this paper is to show that the conventional characteristics to look at to choose a particle are no more the same for a phenomenon such as thermosyphon. Thus, the famous Alumina, compared thanks to tests and modeling, finds itself inferior to the low conductive Lithium Hydroxide in this configuration. Another aim of this article is to discuss the possibility to model nanofluids using single fluid approach and to show the limitations for long terms uses.cf201

The aerodynamics and efficiency of wind pollination in grasses

publication-status: Publishedtypes: ArticleCopyright © 2010 Wiley-Blackwell. This is a postprint of the article published in Functional Ecology, 2010, 24 (4) 706–713. The definitive version is available at www3.interscience.wiley.comSummary 1. Under natural selection for sexual success, the reproductive organs of plants should evolve to become highly effective pollen receptors. Among wind-pollinated plants, larger reproductive structures appear counter-adapted to accumulate pollen by impaction on their windward surfaces, because airborne particles are less able to penetrate the thicker boundary layer of larger targets. Therefore, it has been proposed that wind-pollinated plants with pollen receptors on relatively large structures, like some grasses (family Poaceae), are architecturally adapted to create downstream vortices in which airborne pollen recirculates before accumulating on leeward surfaces. From this basis, the striking diversity among the grasses in the architecture of their flowering stems has been attributed in part to the existence of these contrasting mechanisms for effecting pollen receipt, namely impact collection and recirculatory collection. 2. We investigated the relative importance of impact and recirculatory collection in grasses by analysing a model system in silico using Computational Fluid Dynamics and by conducting in vivo experiments, both in a wind tunnel and outdoors, using two grass species with compact inflorescences, Alopecurus pratensis and Anthoxanthum odoratum. 3. Irrespective of the experimental approach, we found that although pollen recirculated in the leeward eddies of inflorescences, over 95% of the accumulated pollen was collected by windward surfaces. 4. In A. pratensis, the collection efficiency (proportion of oncoming pollen collected) was between 5% and 20%, depending on wind speed in the range 0·5–1·9 m s−1 and these levels conform to those predicted by a mechanistic model of impact collection. 5. Our results demonstrate that grass species with larger inflorescences are, like those with smaller inflorescences, primarily impact collectors of airborne pollen, which suggests that dissimilar reproductive morphology among species cannot be attributed to differentiation in the mode of pollen capture and, instead, requires reference to other factors, such as the need to produce, protect and disperse seeds of different sizes in different environments

Propriétés magnétiques anisotropes du composé Tb0,37Y2,63Fe5O12

Des mesures d'aimantation ont été effectuées sur le composé monocristallin Tb0.37Y2.63Fe5O12 dans l'intervalle de température 4.2K-300K en appliquant des champs magnétiques statiques selon les directions cristallographiques et . La comparaison des variations isothermes de l'aimantation en champs moyens (80 koe) a permis de montrer qu'en dessous de 120K, est bien la direction facile spontanée. La forte anisotropie de l'aimantation qui apparaît en dessous de 60K semble liée à 1'existence d'une structure non colinéaire spontanée des moments de terbium. Lorsqu'un champ magnétique intense (200koe) est appliqué selon la direction , deux transitions magnétiques apparaissent à 4.2K et disparaissent au delà de 16K. La première transition au champ critique Hc1=125koe qui présente les caractéristiques d'une transition du type "crossover" est analysée suivant le modèle théorique de Cooper. La deuxième transition au champ critique Hc2=177koe s'explique par une réorientation de spin des sous réseaux fers en phase oblique. On montre enfin qu'un modèle pour les composés Tb-YIG se rapproche plutôt d'un modèle XY que d'un modèle d'Ising

Magnetic properties of as-cast and nanocrystallized Fe 73,5

This work concerns the study of soft iron-based magnetic materials. More specifically, concerning based iron amorphous materials, it will be done by combining structure and magnetic properties while acting on various parameters, by annealing to characterize the nanocrytallization. An experimental approach of magnetic properties is applied to the amorphous or nanocrystalline ultra soft materials evaluation of power losses, permeability as properties of the cycle of hysteresis. According to the scale of constraints and the nature of heat treatment (without magnetic field or magnetic field), it is induced an anisotropy which changes the magnetization properties. Thus, for ferromagnetic amorphous alloys, the anisotropy induced constraints is eliminated giving rise to a uniaxial anisotropy. FeBSi amorphous type materials can therefore, after introduction of copper (multiplication of germs) and niobium (growth inhibition), get nanocrystallized compositions of Fe73,5Cu1Nb3Si13,5B9 after annealing around of 500 - 600 °C

Evolution thermique de la structure magnétique dans Tb3Fe5O12

L'étude de l'évolution thermique de la structure magnétique du ferrite grenat de terbium (Tb3Fe5O12) a été réalisée par diffraction neutronique entre 4.2K et 614K. Elle a permis de mettre en évidence en dessous de 130K, l'apparition de la structure non colinéaire "en double parapluie" qui existe à 4.2K. Son évolution thermique vers une structure colinéaire de Néel au dessus de 130K est continue. L'application des modèles théoriques de l'analyse de représentation du groupe d'espace rhomboédrique (R-3c) avec k = [000] a montré qu'à toute température entre 4.2K et la température d'ordre TN (560K) la structure magnétique de TbIG appartient à la seule représentation irréductible à une dimension Γ2g(A2g) pour laquelle les caractères des éléments générateurs 3, -1, c sont respectivement +1, +1, -1 : le groupe de Shubnikov correspondant est (R-3c')

Soft Body Impact Simulation on Composite Structures

NRC publication: Ye

Examining the flow of blood in the case of a cerebral aneurysm

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.The aim of the project is to apply a CFD approach to the flow of blood through a cerebral aneurysm which enables the different interactions to be studied in detail. From this study, one hopes to be able to propose to surgeons a more refined and safer method to tackle this condition and to improve the success rate during real time operation. It has been put in place two main orientations by INRIA in collaboration with !CAM in order to resolve the issues of the aneurysm. The suggested methods are as follows: To measure the spread of blood flow by injection of a contrast within the flow and using X ray pulses which take pictures at a rate of 30image/second. This provides a visual perspective of the blood flow inside the area of interest Furthermore, the computer based model will provide parameters as a base for the fluid mechanics calculations. To study different models that already exist to combat the aneurysm in order to carry out simulations on the model of the vascular network in silicone. Various simulations on the reconstructed vascular network model in silicone will be carried out.ksb201

Analysis of flow fields about grass species (poaceae) using CFD approach

Paper presented at the 7th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Turkey, 19-21 July, 2010.Grass species from the Poaceae family exhibit a large variety of their pollen receiving structures, although, they are pollinated by the same agent - the wind. Biologists assume that different architecture types use different pollen capture mechanisms in order to increase the pollen capture efficiency. In this study the flow about computer models of grass plants with four different architectures was investigated using a CFD approach. The goal was to estimate the relevance of microscopic plant structures on the capture efficiency.ksb201

Conifer ovulate cones accumulate pollen principally by simple impaction

In many pine species (Family Pinaceae), ovulate cones structurally resemble a turbine, which has been widely interpreted as an adaptation for improving pollination by producing complex aerodynamic effects. We tested the turbine interpretation by quantifying patterns of pollen accumulation on ovulate cones in a wind tunnel and by using simulation models based on computational fluid dynamics. We used computer-aided design and computed tomography to create computational fluid dynamics model cones. We studied three species: Pinus radiata, Pinus sylvestris, and Cedrus libani. Irrespective of the approach or species studied, we found no evidence that turbine-like aerodynamics made a significant contribution to pollen accumulation, which instead occurred primarily by simple impaction. Consequently, we suggest alternative adaptive interpretations for the structure of ovulate cones