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A novel thermal non-destructive technique based on a Pulsed Flying Spot is presented here by considering in-plane logarithmic processing of the relaxing temperature field around the heat source spot. Recent progress made in optical control, lasers, and infrared cameras permits the acquisition of 2D temperature fields and localized thermal excitation on a small area instead of the entire recorded image. This study focuses on a new method based on spatial logarithm analysis of a temperature field to analyse and measure different parameters, such as the in-plane thermal diffusivity and localization of the spot. In this paper, this method is presented and the first results of heterogeneous anisotropic materials are depicted. The in-plane thermal diffusivity is estimated with an error lower than 4%, and the initial location of the heating spot is determined. [ABSTRACT FROM AUTHOR]

Thermophysical properties mapping in a solid plate from transient temperature imaging analysis is widely developed, but most usual methods are based on very restrictive assumptions such as the independence of the pixels (local one-dimensional diffusion in the sample). The challenge envisioned in this study is to take into account the three-dimensional spatial correlation between pixels. Moreover, the estimation of the thermophysical properties field from two-dimensional measurements is an ill-posed problem, and the practical implementation of the estimation is affected by the large amount of data to be processed. A semi-numerical analysis with spatially random front face excitation is proposed here in order to overcome such problems. A theoretical new method is proposed for the detection of cracks laid perpendicular to the excitation surface. The estimation method is implemented from a spatial autoregressive method. [ABSTRACT FROM AUTHOR]

The main objective of this work is to present a new method for measuring the transverse coefficient of thermal expansion (CTE) of fibers at very high temperature. The difficulty of the measurement is due to the thin fiber diameter (≈10 µm), the low variation with temperature of the fiber diameter (≈10–30 nm), and finally the important range of temperature (300–2800 K). An experimental device was designed for the measurement and an inverse method has been developed for identification. The characterization, with a confidence interval lower than 8%, of tungsten and carbon fibers allows the validation of this device and the related estimation method. [ABSTRACT FROM AUTHOR]

Some analytical solutions of the one dimensional transient coupled heat and mass transfer linear equations in a semi-infinite medium are proposed, based on an extension of the thermal quadrupole formalism, in both axial and radial coordinate systems. A direct relationship is proposed between the local temperature and moisture content, both at wall and inner locations. For a previous characterized medium, these relationships seem to be relevant in order to deduce the moisture content from temperature measurements. Another application would be the transport parameters estimation. [ABSTRACT FROM AUTHOR]

Presents information on a study which estimated the local thermophysical properties of a one-dimensional periodic heterogeneous medium using infrared image processing and volume averaging method. Description of the method; Experimental results; Conclusions.

Ceramic Matrix Composites (CMC) are very attractive for structural applications at high temperatures or under temperature gradients. For these reasons, the mechanical properties must be considered together with the thermophysical properties. The aim of this work is to demonstrate the thermal characterization capabilities of IR thermography in multiscale damage assessment for CMCs. A first device was developed for the thermomechanical characterization at the level of fiber bundle. The longitudinal effective thermal diffusivity was monitored in-situ using the Angström method during a tensile test. In a second device, we implemented flash methods for the estimation of longitudinal and transverse diffusivities during tensile tests of 2D woven SiC/SiC composites. The macroscopic results corroborate the microscopic ones, but they also give complementary indications about composite's behavior. Morevover, these methods offered the possibility to map the distribution of transverse thermal diffusivity. [ABSTRACT FROM AUTHOR]

This work aims to achieve contactless absolute-temperature measurements of infrared-semi-transparent solids using an infrared thermal and spectroscopic imaging technique. The multispectral thermotransmittance coefficient fields in the 3-5 lm wavelength range for Sapphire, KBr, and Silicon are determined to be 6x10-4 K-1, 4x10-4 K-1, and -3x10-3 K-1, respectively. The most interesting result is the high temperature-dependent transmittance coefficient in the middle wave infrared region. With these coefficients, the absolute temperature fields in a range from room temperature to 140°C are shown. [ABSTRACT FROM AUTHOR]

We have combined InfraRed thermography and thermal wave techniques to perform microscale, ultrafast (microsecond) temperature field measurements. The method is based on an IR camera coupled to a microscope and synchronized to the heat source by means of phase locked function generators. The principle is based on electronic stroboscopic sampling where the low IR camera acquisition frequency facq (25 Hz) undersamples a high frequency thermal wave. This technique permits the measurement of the emissive thermal response at a (microsecond) short time scale (microsecond) with the full frame mode of the IR camera with a spatial thermal resolution of 7 μm. Then it becomes possible to study 3D transient heat transfer in heterogeneous and high thermal conductive thin layers. Thus it is possible for the first time in our knowledge to achieve temperature field measurements in heterogeneous media within a wide range of time domains. The IR camera is now a suitable instrument for multiscale thermal analysis. [ABSTRACT FROM AUTHOR]

The main objective of this work is to present a method for measuring the specific heat of single metallic, carbon, and ceramic fibers at very high temperature. The difficulty of the measurement is due to the microscale of the fiber (≈10 μm) and the important range of temperature (700–2700 K). An experimental device, a modelization of the thermal behavior, and an analytic model have been developed. A discussion on the measurement accuracy yields a global uncertainty lower than 10%. The characterization of a tungsten filament with thermal properties identical to those of the bulk allows the validation of the device and the thermal estimation method. Finally, measurements on carbon and ceramic fibers have been done at very high temperature. [ABSTRACT FROM AUTHOR]

In this paper, a method based on Bayesian inference is proposed to conjointly estimate the following two fields of thermophysical parameters. The first is a thermal characteristic time directly linked to the thermal diffusivity and the thickness, whereas the second is the Biot number, which is directly linked to the heat loss and thermal conductivity. This method is robust to noise and leads to very good estimations of the parameters with an algorithm that is very fast and less time consuming than a classical minimization method. At the end of the study, a setup and a methodology are also presented to estimate the average value of the thermal conductivity of an unknown material. [ABSTRACT FROM AUTHOR]

This work reports a multispectral tomography technique in transmission mode (called 3DITI for 3D Infrared Thermospectroscopic Imaging) based on a middle wavelength infrared (MWIR) focal plane array. This technique relies on an MWIR camera (1.5 to 5.5 μm) used in combination with a multispectral IR monochromator (400 nm to 20 μm), and a sample mounted on a rotary stage for the measurement of its transmittance at several angular positions. Based on the projections expressed in terms of a sinogram, spatial three-dimensional (3D) cubes (proper emission and absorptivity) are reconstructed using a back-projection method based on inverse Radon transform. As a validation case, IR absorptivity tomography of a reflective metallic screw is performed within a very short time, i.e., shorter than 1 min, to monitor 72 angular positions of the sample. Then, the absorptivity and proper emission tomographies of a butane-propane-air burner flame and microfluidic perfluoroalkoxy (PFA) tubing filled with water and ethanol are obtained. These unique data evidence that 3D thermo-chemical information in complex semi-transparent media can be obtained using the proposed 3DITI method. Moreover, this measurement technique presents new problems in the acquisition, storage and processing of big data. In fact, the quantity of reconstructed data can reach several TB (a tomographic sample cube of 1.5 × 1.5 × 3 cm3 is composed of more than 1 million pixels per wavelength). [ABSTRACT FROM AUTHOR]

THz waves have shown to be effective for several applications, such as security, non-destructive testing, and water content monitoring for porous materials and food products. This study aims to highlight the use of THz radiation to measure temperature variations of thin insulating materials opaque in the visible or IR range (PVC, PTFE, PMMA, and wood) by using a spectral thermo-transmittance technique. THz wave optical transmittance in materials show high sensitivity to temperature variations. The goal of this paper is to demonstrate the transient temperature gradient dependence of THz transmitted signals inside materials to develop a new contactless method for measuring temperature of thin materials semi-transparent to THz radiation. The principle is based on synchronous detection, using an infrared camera coupled with a THz to infrared thermal converter (TTC) with modulated millimeter-scale waves (2.7 mm). The results show a correlation between the transient temperature and the optical transmittance coefficient. Several types of samples semi-transparent to THz radiation are tested, and the corresponding thermo-transmittance coefficients as reported for PVC, PTFE, PMMA, and wood are respectively 0.805, 0.395, 0.640, and 1.177 K−1 m−1. [ABSTRACT FROM AUTHOR]

The present work presents a fast and simple new experimental method, designed to enhance the observation and characterization of thermal phenomena at microscale. Supercooling of water was carried out in micro-channels and recorded with a high-frequency infrared camera. The method is based on the coupling of microfluidics, infrared thermography, and inverse techniques. The objective is to extract a maximum of information from the experiment to perform advanced characterization of the system. First, a thermal modeling of such a system was written, then the image processing from infrared recordings allowed estimating the thermal properties (diffusivity) and the source term (energy released by the phase change). The novelty of the approach is the ability of measuring the heat released by the phase change and using this displacement to calculate the ice front propagation velocity and thermal properties. This method is appropriate for many other applications and is mainly devoted to the characterization of fluids during phase change at microscale. [ABSTRACT FROM AUTHOR]

Experimental results on the detection of latent water in a honeycomb fiberglass structure using terahertz thermography are presented. These data are compared with data that were obtained using active infrared thermography. [ABSTRACT FROM AUTHOR]

Thanks to infrared thermography, we have studied the mechanisms of CO2 capture by solid adsorbents (CO2 capture via gas adsorption on various types of porous substrates) to better understand the physico-chemical mechanisms that control C02-surface interactions. In order to develop in the future an efficient process for post-combustion CO2 capture, it is necessary to quantify the energy of adsorption of the gas on the adsorbent (exothermic process). The released heat (heat of adsorption) is a key parameter for the choice of materials and for the design of capture processes. Infrared thermography is used, at first approach, to detect the temperature fields on a thin-layer of adsorbent during CO2 adsorption. An analytical heat transfer model was developed to evaluate the adsorption heat flux and to estimate, via an inverse technique, the heat of adsorption. The main originality of our method is to estimate heat losses directly from the heat generated during the adsorption process. Then, the estimated heat loss is taken for an a posteriori calculation of the adsorption heat flux. Finally, the heat of adsorption may be estimated. The interest in using infrared thermography is also its ability to quickly change the experimental setup, for example, to switch from the adsorbent thin-layer to the adsorbent bed configuration. We present the first results tempting to link the thin-layer data to the propagation speed of the thermal front in a millifluidics adsorption bed, also observed by IR thermography. [ABSTRACT FROM AUTHOR]

Abstract: A new method based on the thermal quadrupoles technique for heat transfer modelling in multilayered slabs with heat sources is proposed. Classical thermal quadrupoles use hyperbolic functions and numerical problems occur according to the argument value that depends on thermophysical and geometrical properties as well as characteristics times. We propose a new formulation based on exponential function with negative argument. Using this formulation in the classical equivalent impedance network allows to compute efficiently the thermal behaviour of multilayered slabs with internal heat sources whatever the time and the thermophysical properties. This approach is applied in order to simulate heat transfer in three different multilayered materials with heat sources. These simulations show the capability of such a methodology to simulate time and space multiscale heat diffusion problems. [Copyright &y& Elsevier]

The aim of this work is to present new devices for the measurement of velocity, kinetics, and enthalpy of chemical reactions occurring in a microfluidic chip, co-flow, or droplets flow. The thermal analysis goes from the macroscopic approach by microcalorimetry to microscopic analysis inside the microchannel by IR thermography. Concerning microcalorimetry, the enthalpy is deduced from the measurement of the global heat flux dissipated by the chemical reaction as a function of the molar flow rate. A validation is presented on a well-known acid-base reaction. This device can be combined with an IR camera for local characterization. The processing of the measured temperature fields allows the estimation of properties of great importance for chemical engineers, such as heating source distribution (i.e., the kinetics) of the chemical reaction along the channel. A validation experiment of a temperature field processing method is proposed with the Joule effect. From such a previous experiment, a Peclet field is estimated and used in a further step in order to study an acid-base co-flow configuration. Finally, a first tentative of thermal characterization inside droplets flow during an acid-base chemical reaction is also presented. [ABSTRACT FROM AUTHOR]

Abstract: A model of heat transfer in a SiGe heterojunction bipolar transistor (HBT) at the macro scale is established, that leads to an analytical solution. Modelling is based on the use of integral transforms as the Fourier and Laplace ones. The heat source is assumed as a heat flux applied at the base-collector junction. It is shown that the thermal behaviour of the transistor at the highest frequencies is perturbed by the deep-trench insulation of the device. Finally, it is shown the interest of this model to identify the thermal conductivity of the back-end layer which is treated as a homogeneous medium. [Copyright &y& Elsevier]

GigaHertz (GHz) thermoreflectance technique is developed to measure the transient temperature of metal and semiconductor materials located behind an opaque surface. The principle is based on the synchronous detection, using a commercial THz pyrometer, of a modulated millimeter wave (at 110 GHz) reflected by the sample hidden behind a shield layer. Measurements were performed on aluminum, copper, and silicon bulks hidden by a 5 cm thick Teflon plate. We report the first measurement of the thermoreflectance coefficient which exhibits a value 100 times higher at 2.8 mm radiation than those measured at visible wavelengths for both metallic and semiconductor materials. This giant thermoreflectance coefficient κ, close to 10-3 K-1 versus 10-5 K-1 for the visible domain, is very promising for future thermoreflectance applications. [ABSTRACT FROM AUTHOR]

The aim of this technical brief is to test numerical inverse Laplace transform methods with application in the framework of the thermal characterization experiment. The objective is to find the most reliable technique in the case of a time resolved experiment based on a thermal disturbance in the form of a periodic function or a distribution. The reliability of methods based on the Fourier series methods is demonstrated. [ABSTRACT FROM AUTHOR]