Benjamin Remy

Microscale temperature measurement by the multispectral and statistic method in the ultraviolet-visible wavelengths

The aim of this paper is to present a nonintrusive and optical method based on the classical thermal radiation laws for the measurement of microscale surface temperature. To overcome the diffraction limit, measurements are performed in the ultraviolet-visible range. According to the Planck’s law, emitting energy is low at these wavelengths and only a photonic flux can be measured through a cooled photomultiplier tube and a photon-counting card. The photonic flux exhibits a random character that can be described through well-known statistic laws such as Poisson or normal distributions. It is shown in this paper that the measured signal (photonic flux) agrees well with these statistics laws and that the surface temperature can be obtained either from the average or/and the standard deviation of the photonic flux. A multispectral technique is also introduced to get rid of the knowledge of the local surface emissivity, which is of particular interest for the measurement of temperature in microscale applicatio...

Inverse Conduction Technique in Hankel Domain Using Infrared Thermography: Application to Droplet Stream Quenching a Metal Disk

Cooling of a hot metal by a spray occurs in various situations. Such is the case for a loss of coolant accident in a nuclear reactor, where a generated spray impacts the fuel rod assemblies. Design of an experimental characterization setup for cooling a hot (600°C) disk shape Nickel sample by a stream of monodisperse droplets is presented here. Non-invasive excitation/measurement techniques have been used in order to implement an inverse technique for quantitative estimation of both wall heat flux and temperature: heating is made by induction and infrared thermography is used for rear face temperature measurement. Control and calibration of the losses are key points here: their level is of the same order of magnitude as the flux removed by the droplets. Examples of inversion are presented.Copyright

Alternative and Relevant Representation to Heat Transfer Coefficient for Modeling the Heat Transfer Between a Fluid and a Non-Isothermal Wall in Transient Regime

This paper deals with the relevant model that can be proposed for modeling the interfacial heat transfer between a fluid and a wall in the case of space and time varying thermal boundary conditions. Usually, for a constant and uniform heat transfer (unidirectional steady-state regime), the problem can be solved introducing a heat transfer coefficient h, uniform in space and constant in time that linearly links the surface heat flux and the temperature difference between the wall temperature Tw and an equivalent fluid temperature Tf . The problem we consider in this work concerns the heat transfer between a steady-state fluid flow and a wall submitted to a transient and non uniform thermal solicitations, as for instance a steady-state flow on a flat plate submitted to a transient and space reduced heat flux. We will show that the more interesting representation for describing the interfacial heat transfer is not to define as usually done a non-uniform and variable heat transfer coefficient h(x,t) because as it depends on the thermal boundary conditions, it is not really intrinsic. We propose an alternative approach, which consists in introducing a generalized impedance Z(ω,p) that links in space and time domain the heat flux and the temperature difference through a double convolution product instead of a scalar product. After the presentation of the general problem, the simple case of a stationary piston flow that can be solved analytically will be considered for validation both in thermal steady-state and transient regimes. To conclude and show the interest of our approach, a comparison between a global approach and a numerical simulation in a more complex and realistic case taking into account the thermal coupling with a flat plate will be presented.Copyright

High Temperature Facility Under Vacuum for the Thermal Characterization of Anisotropic Materials

New applications in Aerospace or in Energy industries require the development of new insulating materials at high temperature exhibiting anisotropic properties. Their thermal characterization requires the development of new experimental facilities. The In-Plane measurements can be very difficult due to the thermal coupling that can appear between the sample and air in its vicinity, especially for low conductivity materials. We will show that this problem can be solved either through theoretical models or by working under vacuum. A new facility developed in LEMTA for the thermal characterization at high temperature and under vacuum of anisotropic materials is presented. This type of measurements allows us to get rid of convection effects and non-homogenous oxidation of the material. This method is fast and accurate thank to the inverse method based on an analytical model and allow to estimate through only one experiment the three diffusivities in each direction.Copyright

Estimation of the spatial distribution of high heat flux pulse stimulations through infrared thermography

A theoretical model obtained by using integral transforms is first presented. It is then used for the estimation of the heat flux distribution. As this problem is ill-conditioned, different techniques have been used for its identification, such as the estimation of heat flux spatial frequencies (harmonics by harmonics) or the estimation of the spatial frequencies in the Least Squares sense. These methods have been applied in the case of two different facilities, “TIC / TAC” at CEA-Cesta and the “LUMIX” bench at LEMTA, before being used for the high power electrons beam generator CESAR located in CEA-CESTA.

A Functional Approach of the Experimental Device Transfer Function for Temperature Measurements in the UV-Visible Wavelengths With Multispectral Method

The paper presented here concerns the temperature measurement in the ultraviolet-visible wavelengths. Emphasis is placed on the technique used to determine the temperature, the multi-spectral method. Using this spectral bandwidth is two-fold: on one hand according to the Planck’s law, the measurement sensitivity is very important, and on the other hand, as this interval is narrow, it is possible to make the assumption of constant emissivity. Previous works have shown that most of the error measurements come from the difficulty to know the transfer function of the experimental device. Thus it is proposed here to get rid of the difficulty to know every parameter involved in the transmission function that can be modelled by a quadratic function. Results are compared with experimental measurements and error calculi are also presented.Copyright

Multi-Spectral Techniques Applied for the Measurement of the Microscale Temperature Through Cooled Multiplier Tube in Photon Counting Mode

The aim of this paper is to present a non-intrusive and optical method based on the classical thermal radiation laws for the measurement of microscale surface temperature. To overcome the diffraction limit, measurements are performed in the ultraviolet-visible range. According to the Planck’s law, emitting energy is low at these wavelengths and only a photonic flux can be measured through a cooled Photo-Multiplier Tube (PMT) and a photon-counting card. The photonic flux exhibits a random phenomenon that can be well-described through classical statistic laws such as Poisson or Normal distributions. We show in this paper that the signal we measure agrees well with these laws and that the surface temperature can be obtained either from the average or the standard-deviation of the Photonic flux. Multi-spectral techniques based on either physical and optical techniques like monochromatic filters and reflection/transmission diffraction gratings or digital techniques as a Multi-Channel Analyser (MCA) are proposed to get ride of the knowledge of the local surface emissivity. This is of a particular interest for the measurement of temperature in microscale applications. Finally, temperature measurements carried out on a specific High Temperature Blackbody developed in our laboratory are compared with those obtained through an infrared camera and allow to validate our facility and the presented measurement techniques.Copyright