Estimation of the local convective heat transfer coefficient in pipe flow using a 2D thermal Quadrupole model and Truncated Singular Value Decomposition

The techniques for solving the Inverse Heat Conduction Problem represent useful tools for designing heat transfer apparatuses. One of their most challenging applications derives from the necessity of catching what happens inside a heat transfer apparatus by monitoring the temperature distribution on the external wall of the device, possibly by means of contactless experimental methodologies. The research presented here deals with the application of a solution strategy of the Inverse Heat Conduction Problem (IHCP) aimed at estimating the local heat transfer coefficient on the internal wall surface of a pipe, under a forced convection problem. The solution strategy, formulated for a 2D model, is based on the Quadrupole Method (QM) coupled to the Truncated Singular Value Decomposition approach, used to cope with the ill-conditioning of the problem. QM presents some advantages over the more classical domain or boundary discretization methods as for instance the fact that, being meshless, brings to a reduction of the computational cost. The analytical model, built under the QM, is validated by means of numerical simulations and the numerical outputs are then used as synthetic data inputs to solve the IHCP. The estimation methodology is also applied to experimental data regarding a forced convection problem in coiled pipes. Moreover, the adopted solution technique is compared to other two well-known and consolidated approaches: Finite Element Method coupled to the Tikhonov Regularization Method and Gaussian Filtering Technique. The comparison highlights that, for the problem here investigated, the Quadrupole Method coupled to the Truncated Singular Value Decomposition and Finite Element Method coupled to the Tikhonov Regularization Method perform better than the Gaussian Filtering Technique when the noise level is low, while, for higher noise level values, their efficiency is almost comparable, as it happens in the considered experimental study case

Impact d'une goutte en situation de Leidenfrost - Modélisation des échanges et expériences

Comprendre les mécanismes des interactions gouttes-parois est primordial pour aborder le problème multiphysique que pose le refroidissement par spray. Avant de pouvoir proposer un modèle pertinent permettant de prédire la cinétique de refroidissement d’une pièce de métallurgie refroidie par un spray, il est nécessaire (1) de pouvoir modéliser les échanges de chaleur liés à l’évaporation partielle des gouttes lors de leur impact sur une surface dans des conditions non isothermes, (2) d’étendre ces modèles à des interactions multiples (plusieurs gouttes en interaction) avant (3) d’aborder le problème plus complexe du refroidissement par sprays. Dans cet article, nous présentons les modèles thermiques nous permettant d’estimer les flux (de chaleur et de masse) à l’impact d’une goutte individuelle, puis des résultats expérimentaux concernant l’interaction goutte individuelle-paroi sont analysés. Pour ce faire, un banc d’essais destiné à la mesure du flux extrait en paroi a été conçu ; une mesure par thermographie IR associée à une méthode inverse permet la détermination du flux de refroidissement dû aux gouttes et des visualisations par caméra rapide rendent compte de la topologie des gouttes à l'impact. L'ensemble de ces informations étant nécessaire pour proposer un modèle pertinent et predictif du flux extrait à l'impact

The Sine-Gordon Solitons as a N-Body Problem

We consider the N-soliton solutions in the sine-Gordon model as a N-body problem. This leads to a relativistic generalization of the Calogero model first introduced by Ruijsenaars. We show that the fundamental Poisson bracket of the Lax matrix is quadratic, and the $r$-matrix is a dynamical one. This is in contrast to the Calogero model where the fundamental Poisson bracket of the Lax matrix is linear.Comment: 10 pages LATEX SPhT-93-072; LPTHE-93-4

Instantaneous heat transfers at the impact of a droplet onto a hot surface in the film boiling regime

[EN] Heat and mass transfers at the impact of a droplet onto a hot solid surface are investigated experimentally. Millimetersized water droplets impinges onto a perfectly flat sapphire surface heated at 600°C. The temperature of the liquid inside the droplet is measured using the two-color laser-induced fluorescence (2cLIF) technique. Water is seeded with a temperature-sensitive fluorescent dye, while a nanosecond pulsed laser is used for the excitation of the fluorescence. The ratio of fluorescence signal detected in two appropriate spectral bands allows to determine the liquid temperature. One advantage of this non-intrusive optical technique is that it eliminates adverse effects associated with signal variations caused by droplet shape during its impact. In parallel, the temperature of the solid surface is characterized using infrared thermography. The latter measurements are made possible by the deposition of a nanosize coating of titanium aluminium nitride (TiAlN) on the upper surface of the sapphire window. Thanks to the high frame rate of the IR camera, the time evolution of the heat flux distribution at the solid surface can be reconstructed. A comparison of IR and 2cLIF techniques enable to correlate the heating of the liquid with the cooling of the wall. This reveals that most of the heat removed from the solid surface is devoted to the heating of the liquid, the energy used for liquid vaporization being significantly lower.The authors acknowledge the financial support of the Lorraine region through the CPER ENERBATIN projet.Chaze, W.; Castanet, G.; Caballina, O.; Maillet, D.; Pierson, J.; Lemoine, F. (2017). Instantaneous heat transfers at the impact of a droplet onto a hot surface in the film boiling regime. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 282-289. https://doi.org/10.4995/ILASS2017.2017.4636OCS28228

Heat transfer of droplets impinging onto a wall above the Leidenfrost temperature

Combustion, spray and flow dynamics for aerospace propulsionCombustion, spray and flow dynamics for aerospace propulsionInternational audienceIn aero-engines, droplet/wall interaction phenomena have a considerable influence on the mixture formation process and on wall heat fluxes. Impinging droplets may rebound, splash into secondary droplets or form a liquid film onto the solid surface. Droplet rebound and splashing is also a mechanism for the back penetration of the fuel vapor in the central region of the combustion chamber where the gas temperature is high enough for ignition. This work is an experimental study aiming at characterizing the heat transfers induced by the impingement of water droplets (diameter 80ֱ80 ֭) on a thin nickel plate heated by electromagnetic induction. The temperature of the rear face of the nickel sample is measured by means of an infrared camera and the heat removed from the wall due to the presence of the droplets is estimated using a semi-analytical inverse heat conduction model. In parallel, the temperature of the droplets is measured using the two-color Laser-Induced Fluorescence Thermometry which has been extended to imagery for the purpose of these experiments. The measurements of the variation in the droplet temperature occurring during an impact allow determining the liquid sensible heat. Measurements are performed at surface conditions well above the Leidenfrost temperature. A wide range of Weber numbers corresponding to the bouncing and splashing regimes are tested. Comparison between the heat flux removed from the wall and the sensible heat gained by the liquid allows estimating the heat flux related to liquid evaporation. Results reveal that the respective level of the droplet sensible heat and the heat lost due to liquid vaporization can vary significantly with the droplet sizes and the Weber number

Etude du refroidissement par Sprays d'un cylindre mobile à haute température

Le contrôle de la température de pièces métallurgiques en cours de refroidissement est essentiel puisque la cinétique du refroidissement engendre des transformations cristallines et agit sur les propriétés mécaniques finales de celles-ci. Les sprays permettent d'accroître les échanges thermiques par un mouillage quasi continu de la paroi à refroidir et de les uniformiser. De plus, à échange thermique égal, le débit d'eau utilisé est moindre. Cependant, la physique des échanges thermiques gouttes - parois, en particulier lorsque cette paroi est mobile, doit encore faire l'objet d'études approfondies afin de maîtriser l'ensemble des paramètres qui détermineront l'échange thermique entre le spray et la paroi. Dans cette étude, nous présentons les courbes d'ébullition obtenues pour des sprays plans impactant une surface cylindrique statique ou mobile. Ces résultats sont comparés à des études antérieures sur le refroidissement par impact de jets cohérents

Influence of statistician involvement on reporting of randomized clinical trials in medical oncology

International audienceIdeally, statisticians should be involved in the design, analysis, and reporting of randomized clinical trials (RCTs). This study assessed the impact of a statistician involvement in published medical oncology RCTs between 2005 and 2009. The reporting quality of each publication was rated using the Overall Reporting Quality Score on the basis of either 2001 or 2010 Consolidated Standards of Reporting Trials criteria. A four-question email survey on the statistical design and analysis was sent to the corresponding authors of each trial. Nonresponders were approached a maximum of three times. Overall, 107 responses were received from 357 solicited authors (30%). Corresponding authors from industry-funded RCTs were less likely to respond (51 vs. 65%, P = 0.013). The same person was responsible for statistical design and analyses in 47% of cases. Overall, the statistician involved held a PhD (or equivalent) in statistics in most cases. The statisticians responsible for the statistical design and analysis were listed as coauthors in 68 and 81% of RCT manuscripts. There was no statistically significant impact on manuscript reporting quality of the degree of statistician involvement in manuscript preparation. Fewer trials were reported as positive when the responsible statistician was listed as a coauthor. It is possible that RCTs included in this review are in general of higher quality or were more likely to have a greater level of statistician involvement than smaller, single-arm, or unpublished studies. This imbalance could explain the lack of significant difference observed in the Overall Reporting Quality Score between trials where statisticians were listed as coauthors or not

F.A.R.O.G. FORUM, Vol. 5 No. 8

https://digitalcommons.library.umaine.edu/francoamericain_forum/1064/thumbnail.jp

Characterization and mapping of dwelling types for forest fire prevention

Définition des habitats isolés, diffus et groupés. Méthode de caractérisation et de cartographie de ces types d'habitat dans le contexte de prévention du risque d'incendie. Mise en relation des types d'habitat avec le risque d'incendie. / In a context of forest fire risk , the development of actions concerning wildfire prevention and land management is necessary and essential particularly in wildland urban interfaces (WUI). The term WUI' always includes components such as human presence and wildland vegetation. Both the hazard (probability of fire outbreak, distribution) and the vulnerability of urban areas can be characterized through the spatial organization of houses and vegetation. The first required step is to characterize and map WUI in large areas and at a large scale, which in turn requires qualifying different types of dwellings and mapping them. With this goal in view, the paper presents a brief synthesis of results coming from an exploratory process for the characterization of dwelling types (Lampin et al., 2007), and develops a method based on GIS-geo treatments to characterize different types of dwelling with regard to fire risk. Three types of dwellings were classified: isolated dwellings, scattered dwellings and clustered dwellings, using criteria based on the distance between houses, the size of clusters of houses and housing density, which can be mapped automatically. Within dwelling types, the density value of forest fire ignition changed and was twice as high for isolated dwellings as for clustered dwellings. The spatial organization of dwellings seems to have a real impact on fire occurrence. Thus maps of different dwelling types can be interpreted for use in developing fire fighting strategies or prevention actions concerning end-users such as forest and land planning managers or fire-fighters