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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 the excitation - replacement of the sensor positioning by an image calibration). Furthermore, the considerable number of data produced by the camera is processed using a statistical approach. The validation of the method is made on a homogeneous sample by comparison between the in-plane direction measurements (obtained with the present procedure) and the thickness direction measurements (obtained by the classical flash technique).

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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 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 kinetic and the enthalpy of a strong acid base reaction are monitored in co -flow configuration.

In this work, we extend the classical flash method to retrieve simultaneously the thermal diffusivity and the optical absorption coefficient of semitransparent plates. A complete theoretical model that allows calculating the rear surface temperature rise of the sample has been developed. It takes into consideration additional effects such as multiple reflections of the heating light beam inside the sample, heat losses by convection and radiation, transparency of the sample to infrared wavelengths and finite duration of the heating pulse. Measurements performed on calibrated solids, covering a wide range of absorption coefficients from transparent to opaque, validate the proposed method.

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