Christophe Pradere

Processing of temperature field in chemical microreactors with infrared thermography

This work is devoted to the first analysis of temperature fields related to chemical microfluidic reactors. The heat transport around and inside a microchannel is both convective and diffusive with spatial distribution of source terms and strong conductive effects in the channel surrounding. With simplified assumptions, it is shown that Infrared thermography and processing methods of the temperature frames allow to estimate important fields for the chemical engineers, such as the heating source distribution of the chemical reaction along the channel. A validation experiment of a temperature field processing method is proposed with Joule effect as calibrated source term and non reactive fluids. From such previous experiment, a Peclet field is estimated and used in a further step in order to study an acid-base flow configuration

New temperature field processing from IR camera for velocity, thermal diffusivity and calorimetric non-intrusive measurements in microfluidics systems

Microfluidics is a recent technology where the main advantage is the miniaturisation of the studied phenomena especially in the domain of chemistry. However, measurement techniques (velocity, temperature, etc.) inside microfluidic systems are often difficult to implement. The objective of this work is to design new and efficient measurement tools and methods, in order to obtain a quantitative non-contact calorimeter underflow and at microscales. It is proposed a set of experimental and numerical methods coupling infrared thermography and microfluidics by considering the correlation between the time and space derivative of the temperature fields. These methods allow a transient step-by-step estimation of reduced intermediary fields related to thermal diffusion, fluid flow, channel location and heat sources due to chemical reaction. Finally, with original experimental measurements, electrical calibration and inverse method it becomes possible to map and quantitatively estimate thermophysical parameters used as calibration for a new non-contact and quantitative in situ calorimeter devoted to the study of kinetics and enthalpy of chemical reactions in microfluidics systems.

High speed heterodyne infrared thermography applied to thermal diffusivity identification.

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 f(acq) (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.

Heterodyne method with an infrared camera for the thermal diffusivity estimation with periodic local heating in a large range of frequencies (25 Hz to upper than 1 kHz)

In this article, an aliasing method is introduced in order to measure short time thermal phenomena with infrared thermography devices based on focal plane array systems with snapshot mode possibilities. The principle is to create an electronic stroboscope between the IR camera recording frequency (typically 25 Hz) and the periodic thermal laser excitation at high frequency (between 25 Hz to 10 kHz). It is then possible to record thermal signal variations related to high frequencies at the standard frame rate of classical IR cameras. The main advance of the proposed methods consists in processing the phase lags from the signals recorded on the same exact time scale (snapshot mode) of the camera instead of considering the lag between the laser excitation and the camera response. With the help of this method, an experimental application of periodic point source theory on estimation of the in-plane thermal diffusivity has been tested.

Study of Methodology for Quantitative Thermal Diagnostric of Wall

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.

Mesure de cartographies de teneur en eau par imagerie térahertz

RÉSUMÉ. Cette étude présente une méthode d’imagerie multispectrale Terahertz (THz) permettant la mesure de teneur en eau dans des milieu poreux . Le système TH z est décrit tout comme la méthode de calibration de teneur en eau. La précision de cette technique expérimentale est démontrée en comparant la mesure de profils de teneur en eau en fonction du temps dans de la cellulose et les profils théorique obtenus par un modèle de séchage 1D. Enfin nous présentons les mesures réalisées lors du séchage de pin maritime.