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In this technical note, we present an advanced thermospectroscopic imager based on a Fourier transform infrared (FT-IR) spectrometer and a thermal camera. This new instrument can image both thermal emission and multispectral absorbance fields in a few seconds at a resolution of 4 cm−1 or less. The setup is made of a commercial FT-IR spectrometer (ThermoFisher Nicolet iS50R) synchronized to an IR camera (indium antimonide and strained layer superlattice) as a detector to record the interferograms in each pixel of the images. A fast Fourier transform algorithm with apodization and Mertz phase correction is applied to the images, and the background is rationed to process the interferograms into the absorbance spectra in each pixel. The setup and image processing are validated using thin polystyrene films; during this processing, more than 1750 spectra per second are recorded. A spectral resolution equivalent to that of commercial FT-IR spectrometers is obtained for absorbance peaks valued less than two. The transient capability of the FT-IR thermospectroscopic imager is illustrated by measuring the heterogeneous thermal and absorbance fields during the phase change of paraffin over a few minutes. The complete mechanism of the thermochemical processes during a polymer solidification is revealed through the thermospectroscopic images, demonstrating the usefulness of such an instrument in studying fast transient thermal and chemical phenomena with an improved spectral resolution.

International audience; The main goal of this paper is the estimation of thermal resistive fields in multilayer samples using the classical front face flash method as excitation and InfRared Thermography (IRT) as a monitoring sensor. The complete inverse processing of a multilayer analytical model can be difficult due to a lack of sensitivity to certain parameters (layer thickness, depth of thermal resistance, etc.) or processing time. For these reasons, our present strategy proposes a Bayesian inference approach. Using the analytical quadrupole method, a reference model can be calculated for a set of parameters. Then, the Bayesian probabilistic method is used to determine the maximum likelihood probability between the measured data and the reference model. To keep the processing method robust and fast, an automatic selection of the calculation range is proposed. Finally, in the case of a bilayer sample, both the thickness and resistive 3D layers are estimated in less than 2 min for a space and time matrix of 50,000 pixels by 4000 time steps with a reasonable relative error of less than 5%.

Online first; International audience; Conservation of artworks is of paramount importance nowadays around the world. Clever conservation by using non-destructive testing techniques is highly appreciated by restorers and art historians. Among these, a special set-up working into the infrared region is the flying spot laser thermography technique that uses a punctual stimulus to transfer the heat from the source into the artwork. In this way, the precious surface is gently heated by avoiding any type of damage, such as color changes and/or shrinkage and warpage effects. To the best of our knowledge, the flying spot laser thermography technique, in the configuration proposed, has been used here for the first time in the cultural heritage field. It was applied in combination with terahertz inspection, an emergent technique in the field of art research, completely non-invasive and safe for the operator. The target to be inspected was a panel painting executed by following the rules dictated by the art master Cennino Cennini. Results demonstrated how such an integrated approach is plausible to provide robust information concerning invisible defects to the naked eye.

Knowledge of material emissivity maps and their true temperatures is of great interest for contactless process monitoring and control with infrared cameras when strong heat transfer and temperature change are involved.In this work, we describe the development of a contactless infrared and multispectral imaging technique based on the pyro-reflectometry approach and a specular model of the material reflection.This approach enables in situ and real-time identification of emissivity fields and autocalibration of the radiative intensity leaving the sample by using a black body equivalent ratio.This is done to obtain the absolute temperature field of any specular material using the infrared wavelength.The proposed method is evaluated at room temperature with several heterogeneous samples covering a large range of emissivity values. From these emissivity fields, raw and heterogeneous measured radiative fluxes are transformed into complete absolute temperature fields.

In this work, a novel image-based method is presented to characterize the heat and mass transfer rates in a Hele-Shaw microfluidic reactor. A Fourier transform infrared (FTIR) spectrometer is used in transmission mode in combination with an infrared (IR) camera to simultaneously measure the molar concentration and the thermal fields in the microfluidic chip within few seconds. A classical exothermic NaOH + HCl → NaCl + H2O chemical reaction is used to produce a multiphase flow and a heat source in the reactor. The molar concentration fields of all the species are measured using the IR spectrum in the mid-IR region, and the heat fields are obtained simultaneously from the proper emission. The quantitative aspect of the method is illustrated by comparing the molar concentration profiles to a reactor model, based on the advection-diffusion-reaction equations. The good agreement between the model and experimental data validates the method, and the expected strong diffusion-limited reaction regime in laminar microfluidic reactor is achieved. Thus, the results of this work provide a new and efficient thermospectroscopic imaging method to perform rapid, contactless and in operando heat and mass transfer characterizations in laminar microfluidic reactive flows.

Knowledge of the spatial and temporal distribution of heat flux is of great interest for the quantification of heat sources. In this work, we describe the development of a new ultra-broadband contactless imaging power meter based on electromagnetic to infrared technology. This new sensor and the mathematical processing of images enable the reconstruction of both spatial and amplitude distributions through a wide spectral range of sources. The full modeling of the thermoconverter based on 3D formalism of thermal quadrupoles is presented first before deriving a reduced model more suitable for quick and robust inverse processing. The inverse method makes it possible to simultaneously identify the heat losses and the spatial and temporal source distribution for the first time, to the best of our knowledge. Finally, measurements of multispectral sources are presented and discussed, with an emphasis on the spatial and temporal resolution, accuracy and capabilities of the power meter.

In this paper, we addressed the problem of quantitatively measuring the profile of bilayer media. A contactless thermal profilometry method is proposed. Concretely, this approach corresponds to measuring the interface between two media of a material. An experimental setup is proposed, and a methodology is presented to estimate the profile . Two examples, one numerical and one experimental, are presented in order to validate the method.

In a previous work we developed methods based on Pulsed Flying Spot (PFS) to measure the in-plane thermal diffusivity of (an)isotropic materials. Due to the optical laser scanning system, the effective measurement area is around 5 cm × 5 cm) to obtain a good spatial resolution and to ensure accurate estimated thermal fields. First, to extend the previous method to largest scanning area, we propose to use a robotic arm to analyse large composite samples of complex shape (more than 50 cm × 50 cm). The main advantage of using the robot is to design by Computer Aided Design the complete geometry of the composite sample in order to scan the complete area of the composite and also to orient the non-plane surface of the sample perpendicular to the IR camera field of view and laser spot. Finally, all the area can be thermally characterized and the retrieved in plane thermal diffusivities maps are pasted on the 3D shape to visualise heterogeneity and anisotropy.

International audience; • InfraRed imaging technique for compositional and thermal mapping of transient systems. • Application to a drying droplet of silica dispersion confined between two hydrophobic substrates. • Colloids redistribution due to inhomogeneous drying is highlighted and accurately described. • A numerical statistical inverse method is used to retrieve mutual diffusion coefficient as transient maps. We present an infrared (IR) imaging technique that allows us to retrieve quantitative concentration and thermal maps with relatively fast acquisition times for samples that are evolving in time and have micron-scale spatial resolution. As a proof-of-concept, we image the transient drying kinetics of a μL drop of colloidal suspension in a confined geometry. Quantitative concentration maps inside the drying droplet are retrieved. Transport phenomena such as colloid redistribution inside the droplet due to inhomogeneous drying can be highlighted by this means. A numerical inverse method based on the acquired images that allows one to estimate intrinsic properties of the studied material, such as the collective diffusion coefficient of the mixture, is presented. Such a technique combined with statistical inverse methods provides a useful, non-invasive means of visualizing and estimating parameters of materials evolving in time.

The temperature dependences of both heat capacity and thermal conductivity in nanolamellar Cr2AlC single crystals are measured using modulated photothermal radiometry and compared to first-principles calculations. The electronic contribution to the thermal conductivity of Cr2AlC single crystals is computed ab initio by determining the electronic transport coefficients using density functional theory and by solving the Bloch−Boltzmann transport equation with a temperaturedependent relaxation time. The lattice thermal conductivity is predicted by going beyond the quasi-harmonic approximation and considering renormalized second- and third-order force constant matrices, with anharmonic three-phonon scattering, isotopic scattering, and scattering by carbon vacancies. Isotopic scattering does not modify the lattice thermal conductivity. In contrast, even a small concentration of carbon vacancies induces a substantial decrease of the in-plane lattice thermal conductivity. The anisotropy measured in the thermal conductivity, with a ratio of ∼2 over the whole temperature range, is confirmed theoretically. This anisotropy seems to mainly arise from lattice contributions. A similar anisotropy is expected for other MAX phases with identical layered structures.

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).

The front face photothermal radiometry technique has been improved in order to estimate the thermal conductivity of thin films with better accuracy compared to existing techniques. The experimental procedure is based on the front face response to a nanoseconds laser pulse repeated periodically at high frequency, i. e., a Dirac comb waveform. Averaging the thermal response by considering thousands successive pulses allows improving largely the signal noise ratio. The unknown thermal properties and related experimental parameters are identified by minimizing the gap between the measured signal and the theoretical response that accounts with the pulse waveform, the repetition frequency and the detector transfer function. Minimization is first achieved by implementing first a simplex technique that gives an initial set of values to start the Metropolis–Hastings algorithm in a second step. Application of the proposed methodology is done considering amorphous GeTe film deposited on a Si wafer. It is shown that this experimental method as well as the implementation of the Bayes minimization technique allows to identify the thin film intrinsic thermal conductivity with high accuracy considering some uncertainty on the other parameters assumed to be known.

International audience; Non-destructive testing (NDT) of materials and structures is a very important industrial issue in the fields of transport, aeronautics and space as well as in the medical domain. Active infrared thermography is an NDT method that consists in providing an external excitation to cause an elevation of the temperature field in the material, consequently allowing evaluation of the resulting temperature field at the surface. However, thermal exciters that are used (flash lamps, halogen, lasers) act only on the surface of the sample. On the other hand, several energy conversion systems can lead to the generation of volumetric sources; the phenomena of thermo-acoustics, thermo-induction, thermomechanics or thermochemistry can be cited. For instance, ultrasonic waves can generate volumetric heat sources if the material is viscoelastic or if there is a defect. The reconstruction of these sources is the initial process for the quantification of parameters responsible for the heating. Characterizing a heat source means reconstructing its geometry and the supplied power. Identification of volumetric heat sources from surface temperature fields is a mathematically ill-posed problem. The main cause of the issue is the diffusive nature of the temperature. In this work, 3D reconstruction of the volumetric heat sources from the resulting surface temperature field, measured by infrared thermography, is studied. An analysis of the physical problem enables specifying the limits of the reconstruction. In particular, a criterion on the achievable spatial resolution is defined, and a reconstruction limitation for in-depth sources is highlighted.

The domain of non-destructive testing (NDT) or thermal characterization is currently often done by using contactless methods based on the use of an IR camera to monitor the transient temperature response of a system or sample warmed by using any heat source. Though many techniques use optical excitation (flash lamps, lasers, etc.), some techniques use volumetric sources such as acoustic or induction waves. In this paper, we propose a new inverse processing method, which allows for the estimation of 3D fields of heat sources from surface temperature measurements. This method should be associated with volumetric heat source generation. To validate the method, a volumetric source was generated by the Joule effect in a homogeneous PVC sample using an electrical thin cylindrical wire molded in the material. The inverse processing allows us to retrieve the depth of the wire and its geometrical shape and size. This tool could be a new procedure for retrieving 3D defects on NDT.

International audience; This study has illustrated the potentials of optical and THz infrared thermography in the identification of inserts of different nature in glass fiber reinforced polymer. The inspection efficiency has been comparatively evaluated by applying the Tanimoto criterion. The best test procedure has proven to be one-sided stationary thermal nondestructive testing (TNDT) implementing optical heating with Xenon lamps (Tanimoto criterion 87%). Close values of the Tanimoto criterion have been achieved by using the optical and THz line-scanning procedures. A more subjective evaluation of test procedures has been performed by comparing eight parameters of test performance. The line-scanning TNDT procedure implementing optical heating with halogen lamps seems to be optimal in practical applications.

The Flying-Spot infrared thermography was introduced more than twenty years ago to detect narrow cracks. Recent progress made in optical control, lasers and infrared cameras allows extending the Flying-Spot technique for a quantitative thermal analysis. In this work, we propose a Constant Velocity Flying Spot to measure the in-plane thermal diffusivity of isotropic and anisotropic materials. We demonstrate that the logarithmic temperature profiles perpendicular to the laser motion are parabolic functions from which the thermal diffusivity along this direction is obtained. We have investigated two equivalent experimental configurations: (a) Moving laser with motionless sample and (b) moving sample with motionless laser spot. Both are of practical interest: the first one leads to identify thermal heterogeneities in macroscopic samples and the second one leads to measure the thermal properties of materials in in-line production processes. Measurements performed on calibrated samples (from insulators to good thermal conductors) with both configurations confirm the reliability of the method to measure the in-plane thermal diffusivity with an error less than 4%.

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.

This paper presents an improvement of the classical flash technique that allows measuring the thermal diffusivity of highly diffusive materials without the need of blackbody coatings. The method consists in heating the front face of the sample using a periodic pulses sequence with suitable period and pulse duration. The rear face temperature is recorded simultaneously. An inverse approach is then used to estimate the thermal diffusivity. The underlying model is completely analytical and includes heat transfer and analog signal processing which has been specifically designed for this experiment. A sensitivity analysis and an experiment optimization are performed. Applied to an uncoated copper sample, this method appears to be reliable even in the case of very low optical emission/absorption. Theoretical expectations have been confirmed from experimental data obtained considering copper. Thermal diffusivity has been estimated with less than 4% on both the standard and absolute deviation.

A novel contactless thermal technique based on the Grid Pulsed Flying Spot is presented here to estimate the in-plane fields of the thermal diffusivity in a homogeneous and orthotropic material oriented out of the main axes. The main novelty is to propose an analytical method based on the logarithmic decomposition of the pulsed spot temperature response to simultaneously analyse the location of the spot, the thermal diffusivity and the orientation angle of the orthotropic axes versus the Cartesian axis of the images. Several methods have been proposed to measure the in-plane thermal diffusivities along the main axes of orthotropic materials. To our knowledge, few methods exist that simultaneously estimate the thermal diffusivity tensor in the main axes of orthotropy and the orientation of these main axes. In this paper, we proposed a Logarithmic Ellipsometric Method based on the inverse processing method to estimate the thermal diffusivity from the recording of the transient thermal field at the front face. In this paper, the method is presented, and the first results on the homogeneous orthotropic materials are depicted. The in-plane thermal diffusivity is estimated with an error less than 6%, as is the angular orientation of the orthotropic axis compared to the image axis.

Recently, THz waves have been shown to be an effective technique for investigating the water diffusion within porous media, such as biomaterial or insulation materials. This applicability is due to the sufficient resolution for such applications and the safe levels of radiation. This study aims to achieve contactless absolute water content measurements at a steady state case in semi-transparent solids (wood) using a transmittance THz wave range setup. First, a calibration method is developed to validate an analytical model based on the Beer-Lambert law, linking the absorption coefficient, the density of the solid, and its water content. Then, an estimation of the water content on a local scale in a transient-state case (drying) is performed. This study shows that THz waves are an effective contactless, safe, and low-cost technique for the measurement of water content in a porous medium, such as wood.

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.

We have obtained an analytical expression for the surface temperature of a sample that is moving at constant velocity when it is illuminated by a modulated and focused laser beam, which remains at ...

International audience

Cerium oxide, in addition to its catalytic properties, is also known for its optical properties such as ultraviolet (UV) radiation filtering and a relatively high refractive index ( n &gt, 2 ), which makes it an excellent candidate for multifunctional coatings. Here, we focus on the optical properties of thin deposits (≲2 &mu, m) of densely packed C e O 2 nanoparticles, which we assemble using two evaporation-based techniques: convective self-assembly (CSA, a type of very slow blade-coating) to fabricate large-scale coatings of controllable thickness&mdash, from tens of nanometres to a few micrometers&mdash, and microfluidic pervaporation which permits us to add some micro-structure to the coatings. Spectroscopic ellipsometry yields the refractive index of the resulting nano-porous coatings, which behave as lossy dielectrics in the UV-visible regime and loss-less dielectrics in the visible to infra-red (IR) regime, in this regime, the fairly high refractive index (&asymp, 1.8) permits us to evidence thickness-tunable anti-reflection on highly refractive substrates, such as silicon, and concomitant enhanced transmissions which we checked in the mid-IR region.

International audience

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In this paper is presented an IR imaging technique allowing one to retrieve quantitative concentration and temperature maps with relatively fast acquisition times of samples evolving in time. A model study is realized based on the drying of a drop of colloidal dispersion in confined geometry and quantitative maps of colloid volume fraction and temperature everywhere in the dorp are retrieved. Finally, a secondary technique of IR tomography is presented to extend the setup sensitivity to the thickness of the sample and 3D tomographs of both thermal emissivity and IR absorbance of a silica gel are constructed numerically.

Constant Velocity Flying-Spot thermography consists in scanning the sample surface by a focused CW-laser spot moving at constant speed. This technique was designed to study large surfaces in short times. In this work, we propose a method, based on a Flying-Spot thermography setup, to size the width of vertical cracks by fitting the temperature profile along the line that contains the center of the laser spot and is perpendicular to the crack to its analytical expression. This method is also valid in the opposite configuration, where the laser spot remains at rest and the sample is moving at constant velocity. This configuration is useful for in-line inspection in factories, for detecting and sizing cracks in real time, without stopping the production chain. Experimental measurements on stainless steel samples containing calibrated vertical cracks confirm the validity of the method to measure the crack width with high accuracy, even for submicronic wide cracks.

Non-destructive testing (NDT) of materials and structures is a very important industrial issue in the fields of transport, aeronautics and space as well as in the medical domain. Active infrared thermography is an NDT method that consists of providing an external excitation to cause an elevation of the temperature field in the material, consequently allowing evaluation of the resulting temperature field at the surface. However, thermal exciters that are used (flash lamps, halogen, lasers) act only on the surface of the sample. On the other hand, several energy conversion systems can lead to the generation of volumetric sources, the phenomena of thermo-acoustics, thermo-induction, thermomechanics or thermochemistry can be cited. For instance, ultrasonic waves can generate volumetric heat sources if the material is viscoelastic or if there is a defect. The reconstruction of these sources is the initial process for the quantification of parameters responsible for the heating. Characterizing a heat source means reconstructing its geometry and the supplied power. Identification of volumetric heat sources from surface temperature fields is a mathematically ill-posed problem. The main cause of the issue is the diffusive nature of the temperature. In this work, 3D reconstruction of the volumetric heat sources from the resulting surface temperature field, measured by infrared thermography, is studied. An analysis of the physical problem enables specifying the limits of the reconstruction. In particular, a criterion on the achievable spatial resolution is defined, and a reconstruction limitation for in-depth sources is highlighted.

In viscoelastic media, mechanical energy is partially converted to thermal energy. Thus, the vibration of a structure implies that there are thermal heat sources due to mechanical dissipati...

In this paper, the problem of the quantitative characterization of thermal resistance fields in a multilayer sample is addressed by using the classical front face flash method as the thermal excitation and infrared thermography (IRT) as the monitoring sensor. In this challenging problem, the complete inverse processing of a multilayer analytical model is difficult due to the lack of sensitivity of some parameters (layer thickness, depth of thermal resistance, etc.) and the expansive computational iterative processing. For these reasons, the proposed strategy is to use a simple multilayer problem where only one resistive layer is estimated. Moreover, to simplify the inverse processing often based on iterative methods, an asymptotic development method is proposed here. Regarding the thermal signal reconstruction (TSR) methods, the drawback of these methods is the inability to be quantitative. To overcome this problem, the method incorporates a calibration process originating from the complete analytical quadrupole solution to the thermal problem. This analytical knowledge allows self-calibration of the asymptotic method. From this calibration, the quantitative thermal resistance field of a sample can be retrieved with a reasonable accuracy lower than 5%.

A transient 3D thermal model based on the thermal quadrupole method, coupled to ray tracing analysis, is presented. This methodology can predict transient temperature maps under any time-fluctuating irradiance flux&mdash, either synthetic or experimental&mdash, providing a useful tool for the design and parametric optimization of concentration photovoltaics systems. Analytic simulations of a concentration photovoltaics system thermal response and assessment of in-plane thermal gradients induced by fast tracking point perturbations, like those induced by wind, are provided and discussed for the first time. Computation times for time-resolved temperature maps can be as short as 9 s for a full month of system operation, with stimuli inspired by real data. Such information could pave the way for more accurate studies of cell reliability under any set of worldwide irradiance conditions.

A new focus is given regarding the use of the quadrupole technique to solve heat diffusion problems with heat source in layered structures. The thermal impedances formalism is used that allows representing the heat transfer in such systems as impedances network. This approach offers a fast and accurate mean to calculate the average temperature of the heat source according to its spatial local and its transient evolution.

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Non-destructive thermal diagnosis of walls is a crucial theme for the renovation of old buildings, the examination of building structures and the accreditation of new buildings. Nevertheless, there are very few diagnostic methods for the characterization of thick walls. In this study, an innovative approach that combines terahertz radiation method and thermal probe method is proposed. Firstly, a method using THz (terahertz) radiation is investigated and primary experimental results are shown. This THz radiation method has a large potential to characterize the dense building materials (concrete, plaster) in a short time. However, this method is less sensitive to the light insulating materials which are totally transparent to such THz radiation, and it is also impossible to identify the structure and layer order in the case of multilayer walls. Then, based on the classical thermal probe method, three multilayer walls formed of plaster, concrete and insulation materials which are common components of building walls are considered. A short time thermal probe method with an assumption of semi-infinite boundary condition is innovatively proposed. This thermal method is able to identify the first layer of wall and characterize light insulating materials or insulating and slightly capacitive materials. Therefore, with the two methods, both the dense materials and light insulating materials can be characterized. Finally, a combined application of the two methods is discussed and analyzed.

The aim of this paper is to present an experimental infrared thermography study of a well-known chemical reaction in a biphasic millifluidic droplet flow. Through a simple thermal evaluation, it is possible to characterize the kinetics and enthalpy of exothermic chemical reactions. The originality of this work lies in the combination of two versatile techniques and a thermal evaluation based on a homogenized thin body approximation to perform calorimetric estimations. This novel calorimeter requires thermal calibration to estimate the heat losses. A correlation method was therefore applied for the simultaneous estimation of the heat source ( ϕ ) and the characteristic coefficient due to convective heat transfer effects ( H ). This methodology was applied to an acid-base chemical reaction performed at different flow rate ratios. The reaction enthalpy was estimated with an error smaller than 2% compared with the literature value. In addition, the procedure for the estimation of the mixing kinetics of the reaction is revealed by the time-integrated heat flux. Finally, a non-contact thermal calorimeter based on millifluidic and IR thermography was developed. The proposed methodology is demonstrated to be a convenient and powerful tool for the characterization of chemical reactions performed in a droplet flow.

The purpose of this work was to develop a non-contact characterization technique based on infrared thermography (IRT) for millifluidics reactors dedicated to exo or endothermal chemical reactions. An acid (HCl)-base (NaOH) reaction was performed using concentric injection of the reactants. Droplets of small volume (μL) were generated and were carried downstream by inert oil in TEFLON tubing. A color indicator was added to enable monitoring of the reaction evolution by visible imaging. Thus, coupled IRT and visible imaging are used to characterize the reaction. From the IRT temperature fields, a thermal evaluation enables estimation of the enthalpy with less than 2% error. In addition, characterization of the kinetics and the mixing dynamics was performed by both techniques. It was shown through a quantitative relation that the kinetics and mixing dynamics are predicted with 90% precision. In addition, the dynamics inside the droplets can be represented as a diffusion phenomenon, where species are carried inside with an apparent diffusion coefficient that is more than 10 times the molecular coefficient 3 × 10−9 m s−1. Moreover, the mixing time of millifluidic droplets for a given channel (i.e., fixed inner diameter) is influenced by the droplet length and velocity. In contrast, there is no influence of the droplet length on the apparent diffusion coefficient for a given constant velocity. Finally, it was shown through characterization of the diode reaction that this novel non-intrusive technique based on millifluidic and IRT is a convenient and powerful tool for the characterization of biphasic flows, highly exothermic chemical reactions and other physical phenomena such as phase changes.

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 flui...

International audience; The purpose of this article is to present a new calibration procedure for spectroscopic measurements using an infrared focal plane array (IRFPA) spectrometer on highly opaque middle-wave infrared (MWIR) media. The procedure is based on the properties of the IRFPA camera and especially the integration time (IT), which is the main parameter that can be adjusted to control the sensitivity of the measurements. The goal of the paper is to experimentally validate this dependence with the direct reference intensity light coming out of the IR monochromator in order to predict the spectrum shape and intensity level in a range out of the camera saturation. This method allows determining spectrum used as background for transmittance calculation. It has been applied in the case of measurement of water transmittance, which is a highly opaque medium and whose measurement requires high ITs. The main result is the ability to take an IR spectroscopic imaging measurement through 300 µm of water and the determination of its transmittance with sufficient sensitivity due to the proposed calibration procedure. This procedure allows the possibility of transitory studies in heterogeneous aqueous media.

International audience; Silver nanowire transparent electrodes have shown considerable potential to replace conventional transparent conductive materials. However, in this report we show that Joule heating is a unique and serious problem with these electrodes. When conducting current densities encountered in organic solar cells, the average surface temperature of indium tin oxide (ITO) and silver nanowire electrodes, both with sheet resistances of 60 ohms/square, remains below 35 °C. However, in contrast to ITO, the temperature in the nanowire electrode is very non-uniform, with some localized points reaching temperatures above 250 °C. These hotspots accelerate nanowire degradation, leading to electrode failure after 5 days of continuous current flow. We show that graphene, a commonly used passivation layer for these electrodes, slows nanowire degradation and creates a more uniform surface temperature under current flow. However, the graphene does not prevent Joule heating in the nanowires and local points of high temperature ultimately shift the failure mechanism from nanowire degradation to melting of the underlying plastic substrate. In this paper, surface temperature mapping, lifetime testing under current flow, post-mortem analysis, and modelling illuminate the behaviour and failure mechanisms of nanowires under extended current flow and provide guidelines for managing Joule heating.

A novel infrared (IR) thermo-spectroscopic imaging technique is applied to the simultaneous measurements of IR transmittance spectroscopic images and thermal emission images of heat and mass transfers of styrene monomer polymerization in microfluidics. The heat released is observed in the mixing layer between two laminar flows of styrene monomer and toluene containing an initiator for polymerization. The concentration of chemical species and the independently measured temperature distribution within the mixing layer are determined at the microscale. This is the first report, of such a non-invasive method, to determine both the chemical composition and temperature distribution in microfluidic chemical reactions.

International audience; Non-destructive evaluation (NDE) method has been popularly used for thermal diagnosis of building envelop in order to retrofit old buildings, detect civil engineering structures and accredit new buildings. The infrared thermography technique has been widely applied in the NDE method. In order to develop new solutions for diagnostic of local thermal performance, experiments were carried out on two cases of multi-layer walls. Experimental results of emissivity, temperature, and heat fluxes will be shown and analyzed in this article. The main originality of this work is to try to compute the front face temperature response to transient periodic heating by computing the front face pulse response. Such front face pulse response is obtained by a deconvolution method and a TSVD inverse method. The thermal properties of the wall will be characterized through the opotimization method based on the thermal quadrupoles model.