Development and validation of a numerical tool for the simulation of the temperature field and infrared radiance rendering in an urban scene

International audienceWe present a numerical tool aimed at simulating infrared images of an urban environment, by solving the direct heat transfer problem, and then computing the radiance rendering at the sensor level. SOLENE (Cerma, Nantes) was coupled with two software packages developed at ONERA: SUSHI (Simulation in Urban Scene of Heat dIffusion) and MOHICANS (MOdélisation Hyperspectrale d'Images en entrée Capteur pour l'ANalyse et l'inversion du Signal) for realizing this task. SUSHI is also used for computing the surface temperatures: either a 1D model or a 2D model is used. We present the whole software chain, its validation by software and experimental analysis

An experimental identification of line heat sources in a diffusive system using the boundary element method

International audienceThis paper deals with an inverse problem which consists of the experimental identification of line heat source strength in an homogeneous solid using temperature measurements. An inverse formulation using the boundary element method, is used to identify the strength of line heat sources. In the case of multiple sources identification the location is assumed to be known but, in the case of a single source, an iterative algorithm for the location identification is proposed. The experiment consists of the identi®cation of the power dissipated by Joule effect in one or two thin wires placed in a long square section cement bar. The measurements necessary to solve the inverse problem are provided by thermocouples for the internal temperatures and by infrared thermography for the superficial temperatures. A time regularization procedure associated to future time steps is used to correctly solve the ill-posed problem

Infrared visualization of thermal motion inside a sessile drop deposited onto a heated surface

International audienceDrop evaporation is a basic phenomenon but the mechanisms of evaporation are still not entirely clear. A common agreement of the scientific community based on experimental and numerical work is that most of the evaporation occurs at the triple line. However, the rate of evaporation is still predicted empirically due to the lack of knowledge of the governing parameters on the heat transfer mechanisms which develop inside the drop under evaporation. The evaporation of a sessile drop on a heated substrate is a complicated problem due to the coupling by conduction with the heating substrate, the convection/conduction inside the drop and the convection/diffusion in the vapor phase. The coupling of heat transfer in the three phases induces complicated cases to solve even for numerical simulations. We present recent experimental results obtained using an infrared camera coupled with a microscopic lens giving a spatial resolution of 10 mu m to observe the evaporation of sessile drops in infrared wavelengths. Three different fluids fully characterized, in the infrared wavelengths of the camera, were investigated: ethanol, methanol and FC-72. These liquids were chosen for their property of semi-transparency in infrared, notably in the range of the camera from 3 to 5 mu m. Thus, it is possible to observe the thermal motion inside the drop. This visualization method allows us to underline the general existence of three steps during the evaporating process: first a warm-up phase, second (principal period) evaporation with thermal-convective instabilities, and finally evaporation without thermal patterns. The kind of instabilities observed can be different depending on the fluid. Finally, we focus on the evolution of these instabilities and the link with the temperature difference between the heating substrate and the room temperature. (C) 2010 Elsevier Inc. All rights reserved

Heat source estimation in low diffusive materials

International audienceIn this work, a method to estimate unsteady 2D heat sources is developed. The sources are estimated from Infra-Red (IR) temperature mapping on the front face of thermally thin material. A comparison of the estimation accuracy as well as the evaluation of time cost is also carried out between a direct method (coupled with filtering techniques) and an iterative method (of conjugate gradient type). The present work was realised on experimental data

In-situ estimation of the thermal resistance of carbon deposits in the JET tokamak

International audienceThe present paper deals with the heat flux estimation and the thermal characterization of the poorly attached Surface Carbon Layer (SCL) to the Plasma Facing Component (PFC) observed on the inner vertical tiles of the JET Tokamak. A nonlinear unsteady calculation combined with the Conjugate Gradient Method (CGM) and the adjoint state is achieved in order to estimate the time variation of the heat flux necessary to characterize in situ the space and time variations of the thermal resistance Rth of the SCL. The method is applied on L mode power step plasma discharge (#58850). One embedded thermocouple (TC) is used to the heat flux estimation (another embedded TC is used for validate the estimation) and infrared (IR) measurements coming from the IR camera KL3 are used to estimate the SCL thermal resistance. The estimated SCL thermal resistance is compared to the history of the strike point location to highlight the correlation between the spatial distribution of the SCL thermal resistance and the location of the maximum heat flux

Successive identification of surface heat flux and thermophysical properties of plasma facing components inside the JET tokamak: numerical feasibility

6th European Thermal Sciences Conference (Eurotherm), Poitiers, FRANCE, SEP 04-07, 2012International audienceWe present here the numerical feasibility of using two thermal diagnostics (IR, surface and embedded thermocouple temperature measurements), that outfit the same carbon tile inside the JET Fusion reactor and whose combination enables to identify, on one hand, a surface heat flux history and, on the other hand, the spatial and time variation of the thermal resistance of an unknown deposited surface carbon layer (SCL). The Conjugate Gradient Method (CGM) and the adjoint state were applied to perform these two identifications

Characterization of time varying thermophysical property of a surface layer: Numerical feasibility for JET tokamak tiles

International audienceThe present paper deals with the thermal characterization of the Surface Carbon Layer (SCL) usually poorly attached to the Plasma Facing Component (PFC) inside the nuclear fusion machines (Tokamak). A nonlinear unsteady calculation combined with the Conjugate Gradient Method (CGM) and the adjoint state is achieved in order to characterize in situ the time variation of the thermal resistance Rh of a surface layer. A numerical feasibility is presented with a realistic virtual experiment design. The accuracy of the method is examined by using simulated exact and inexact infrared measurements obtained on the SCL surface. The advantages of applying the CGM with the adjoint state in the present study, are that no prior information is needed on the time variation and the initial guess of the unknown thermal resistance. (C) 2012 Elsevier Ltd. All rights reserved