Jean-Christophe Batsale

Measurement of thermal diffusivities through processing of infrared images

The measurement of the thermal diffusivity of a thin layer in the direction of its plane is usually a difficult operation. The standard ‘‘flash technique’’ is very appropriate for diffusivity measurement in the direction of the thickness of the sample but adaptations of this method to in‐plane measurements remain very sensitive to the position and form of heat excitation and temperature sensors. The new procedure proposed here consists of applying any geometrically nonuniform heat impulse on the front face of the sample and recording the entire transient temperature image on the rear face thanks to an infrared camera. The influence of axial diffusion can be avoided for periods much longer than the axial diffusion characteristic time. Integral transforms on the radial space variables (Fourier transform) are very suitable for treating the temperature field and to estimate radial diffusivity. The main advantage of this method is to avoid any experimental precaution (no knowledge of the geometrical form of th...

Characterization of a heat flux sensor using short pulse laser calibration

A method to calibrate classical heat flux sensors is presented. The classical approach to measure the temperature inside a known material by using a thermocouple fails when the measurement time is very short. In this work the surface heat flux is determined by solving the inverse heat conduction problem using a noninteger identified system as a direct model for the estimation process. Using short pulse laser calibration measurements the crucial design aspects of the sensor that play a significant role when assuming one-dimensional, semi-infinite heat transfer have been accounted for. The theoretical approach as well as the calibration results are presented and comparisons to the classical approach and results from finite element modeling are shown. It is concluded that the new method ameliorate the heat flux sensor significantly and extend its application to very short measurement times.

Microscale thermography of freezing biological cells in view of cryopreservation

The aim of this work is to present a device for the measurement of biological living tissues during freezing by infrared camera. Under simplified assumptions, it is shown that infrared thermography measurements and two-dimensional microscale thermal processing methods of the temperature frames allow to estimate important thermophysical fields for the cryopreservation of living tissues, such as the heating source distribution of the latent heat released from biological cells and the thermal properties during freezing. This work is related to the analysis of thermal source terms occurring during freezing of biological tissues from the processing of experimental temperature fields obtained by infrared thermography. Such information is very important in order to understand and improve the heterogeneous solidification phenomena during cryopreservation processes. A new method is proposed here in order to estimate the 2D mapping of source terms and thermal diffusivity during freezing. Such source terms (space and time distributions) are strongly related to the thermal diffusivity mapping which control the 2D in plane diffusion into the tissue.

A millifluidic calorimeter with InfraRed thermography for the measurement of chemical reaction enthalpy and kinetics

The aim of this work is to present an infrared calorimeter for the measurement of the kinetics and the enthalpy of high exothermic chemical reactions. The main idea is to use a millifluidic chip where the channel acts as a chemical reactor. An infrared camera is used to deduce the heat flux produced by the chemical reaction from the processing of temperature fields. Due to the size of the microchannel, a small volume of reagents (ml) is used. As the chemical reagents are injected by a syringe pump, continuous experiments are performed with a very good control of the reagents mixing. A specific injection system enables to perform two flow configurations: co-flow and droplets. Thanks to the thermal isoperibolic conditions, the chemical reaction can be easily characterized with a previous specific calibration. Here, the gradual mixing by species diffusion and the enthalpy of a strong acid base reaction are monitored in co - flow configuration.

Photothermal converters for quantitative 2D and 3D real-time TeraHertz imaging

Recent advances for the measurement of TeraHertz (THz) radiation by using original IR temperature flux sensors are presented. The bolometer principle is used for designing simple thermal converters for THz radiations (measurement of the temperature increase of a sensitive absorber). Most of these sensors are efficient, sensitive and fast enough for quantitative measurement of THz source power as well as for 2D and 3D THz imaging. By combining optical and thermal technologies, we extend and adapt the use of thermal sensors to large THz wavelength till 3 mm (0.1 THz). A large variety of mono- or arrayed- thermal sensors is used and optimized for real-time room temperature THz imaging using adapted IR focal-plane microbolometers array (FPMA) camera. Optimisation and adaptation of such FPMA is discussed and a new arrayed prototype device of THz-Thermal Converter, “TTC”, for full-field real-time THz imaging is presented. This small size, low cost and efficient prototype design is discussed from the thermal point of view and is characterized using a compact powerful THz source. Their sensitivity is evaluated and the obtained 2D and 3D images clearly illustrates the high potential of this new kind of THz camera. Finally, it is shown that non-arrayed extended plane TTCs (EMIR sensitive screens) coupled to FPA cameras produce THz images free of diffraction phenomena.

Mesure de coefficient d'échange thermique en milieux hétérogènes par thermographie infrarouge application d'un modèle à deux températures☆

Abstract In this paper, a two-equation model is used to describe macroscopic heat transfer in heterogeneous media (porous media, composite materials, etc.) when there is local thermal non-equilibrium between the two constitutive phases. Such macroscopic models involve a heat exchange coefficient between the phases. The objective of this study is to propose an experimental methodology to measure this heat transfer coefficient. The experimental technique proposed here is based on the analysis of infrared images obtained from 2D, periodic, two-phase materials submitted to an instantaneous heat pulse. An integral transformation of the macroscopic transfer equations, taking into account the parietal heat exchange with the surroundings leads to a simple analytical expression between the macroscopic temperatures relative to each phase. From the temporal experimental evolution of these macroscopic temperatures, it is possible to estimate three independent parameters, and to separate the parietal exchange from the exchange between the two phases. This approach has been validated by the comparison of experimental results and theoretical values.

Absolute self-calibrated room-temperature terahertz powermeter

Coupling optical and thermal properties of a terahertz (THz) thermal converter based on the Seebeck effect provides an unsupplied room-temperature measuring device dedicated to THz power metrology. Performance characteristics such as broadband response (0-30 THz), high sensitivity (<25 μW·Hz(-0.5)), and the possibility to develop an internal absolute self-calibration estimated at 9.93 W·V(-1) are reported. Advantages and drawbacks of this THz powermeter are discussed.

3D transient temperature measurement in homogeneous solid material with THz waves

The first imaging system that is able to measure transient temperature phenomena taking place inside a bulk by 3D tomography is presented. This novel technique combines the power of terahertz waves and the high sensitivity of infrared imaging. The tomography reconstruction is achieved by the 3D motion of the sample at several angular positions followed by inverse Radon transform processing to retrieve the 3D transient temperatures. The aim of this novel volumetric imaging technique is to locate defects within the whole target body as well as to measure the temperature in the whole volume of the target. This new-fashioned thermal tomography will revolutionize the non-invasive monitoring techniques for volume inspection and in-situ properties estimations.

Non-contact temperature field measurement of solids by infrared multispectral thermotransmittance

This work aims to achieve contactless absolute-temperature measurements of infrared-semi-transparent solids using an infrared thermal and spectroscopic imaging technique. The multispectral thermo-transmittance coefficient fields in the 3–5u2009μm wavelength range for Sapphire, KBr, and Silicon are determined to be 6u2009×u200910−4 K−1, 4u2009×u200910−4 K−1, and −3u2009×u200910−3 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 140u2009°C are shown.

Pulsed flying spot with the logarithmic parabolas method for the estimation of in-plane thermal diffusivity fields on heterogeneous and anisotropic materials

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.