Mesures de conductivité thermique des fluides et microfils par modèles

Mesures de conductivité thermique des fluides et microfils par modèles à températures moyennes et traitement d’images infrarouges Olivier Fudym, Francisco Sepulveda RAPSODEE UMR 2392 CNRS, Ecole des Mines d’Albi, Albi, France Christophe Pradère, Jean-Christophe Batsale TREFLE-ENSAM, UMR 8508 CNRS, Bordeaux, France Eurotherm Seminar N° 81 Reactive Heat Transfer in Porous Media Ecole des Mines d’Albi, FranceJune 4 – 6, 2007

Introduction Joint Program « thermal characterization in microfluidics » Toulouse: LAAS, LGC, EMAC Bordeaux: CPMOH, TREFLE, LOF Increasing development of microfluidic chemical reactors Thermal characterization of microchannel reactors Retrieving reaction dynamics from the analysis of the thermal sources distribution Microsensors Photoreflectance imaging Infrared images processing Full field method « micro » and « macro » Average temperature model

Microscale heat transfer in MEMS • Microfabrication technique originally devoted to electronics have reach spectacular advances (microreactors, microsensors…) • Advantages of MEMS: • Low fluid and solids mass requirements, small volumes, low cost fabrication… • Heat transfer: high speed of diffusion, confinement of heat sources • Advantages of IR thermography on MEMS • Non intrusive • Possibilities of processing a large amount of data related to heat transfer • … • BUT • Measurement noise • Drawbacks due to small scales

T(x,t) x Main assumptions and convenient method related to small scales Creation of a mainly 2D temperature field related to a 1D macroscopic field IR Conductive layer with uniform emissivity cooling heating Thermally insulating substrate Estimation of fluctuations around a macroscopic gradient

1-Analysis of the perturbation of a macroscopic field-Transport in periodic heteroeneoux media The relation between macroscopic and local field leads to a closure problem. It needs to consider stationnary a closure tensor b , such as: and M. VARENNE, J.C. BATSALE et C. GOBBÉ, 2000, Estimation of a local thermal conductivity field of a plane heterogeneous medium with infrared images and volume averaging method, High Temperatures - High Pressures, Vol 32, pp329-336

Instantaneous temperature fields Closure fields Estimation of conductivity fields

2-Caracterization of microchannels reactors Microfluidic experiments

Acid Infrared camera InSb sensor Base Field Estimation for Local Mapping PDMS resin Heating film Syringe Pump (1.5 - 5 .2 µm) Lens Glass microchannel

Processing temperature fields in a microfluidic chip Temperature fields without flow with flow

Transient evolution Macroscopic gradient

Temperature difference between initial and perturbed field

Application to a chemical reaction characterization: When Pe of the system is estimated, it is then possible to estimate any source term from a chemical reaction. Temperature field Tc, at Q = 1000 µlh Chemical source term at Q = 1000 µlh Pradère C., Joanicot M., Batsale J-C., Toutain J., Gourdon C., (2006). Processing of temperature field in chemical microreactors with infrared thermography, QIRT Journal 3 117-135

Thermal characterization of microchannel reactors from averaged two-temperature model and infrared images processing • Introduction • Field Estimation for Local Mapping • Macroscopic characterization from averaging • Conclusions

Infrared Imaging System Glass cover Microchannel PDMS Resin Microchannel y e2 e1 x Heating resistive film Macroscopic characterization from averaging Sample = one or few pixels width 200 µm Object almost not visible in the thermal image

x Microchannels Heating resistive film y Macroscopic characterization from averaging Temperature field Laplacian of Temp. field Bias in the estimation

x Substrate plate v g1(y) Reactive fluid y Thermal Quadrupole formalism i = 1, 2 Integral transforms Generalized heat source term Generalized frequency Maillet D., André S., Batsale J.C., Degiovanni A., Moyne C. Thermal quadrupoles : Solving the heat equation through integral transforms, John Wiley, 2000

G1e1 Thermal Quadrupole formalism Source term « Input x = 0 » « Output = interface » Analogical network

x G1e1 G2e2 y Analytical Averaged Two Temperature model 1 2 Analogical network

x Substrate plate v g1(y) Reactive fluid y g(y) g(y) Heating zone : 10 – 50 mm Température difference along the microchannel T1 – T2 y

(K) Macroscopic characterization from averaging fitted with Heat losses H T1 – T2

Macroscopic characterization from averaging Retrieved Heat Source O. Fudym, C. Pradère, J.C. Batsale , An analytical two-temperature model for convection-diffusion in multilayered systems. Application to the thermal characterization of microchannel reactors. Accepted in Chemical Engineering Science, may 2007, DOI : http://dx.doi.org/10.1016/j.ces.2007.04.037

microwire thermal conductivity measurement Simulated Temperature field +

y microwire thermal conductivity measurement Average temperature profile Retrieved Thermal conductivity y

T(x,t) x Perspective: Analysis of a perturbation caused by a thin graphite cylinder on one insulating layer with in plane gradient IR Thin conductive cylinder Metallic layer Thermally insulating substrate heating cooling Estimation of fluctuations around a macroscopic gradient

Perturbations of of some fibers In a uniform field

Other perspectives: Analysis of arborescent channel networks Silicon thin plate 200 µm 400 µm 600 µm 800 µm 1 mm Fluid input Fluid outputs

Conclusion and perspectives -La perturbation thermique d’un fil de faible diamètre peut entraîner une modification du champ de température sur un large diamètre dans un milieu sous gradient thermique. -Intérêt des moyennes de températures pour analyser des perturbations de conductivité thermique -Perspectives: Mesure de fils de faible diamètre ou de microcanaux, Caractérisation de milieux filamentaires arborescents

Mesures de conductivité thermique des fluides et microfils par modèles

Mesures de conductivité thermique des fluides et microfils par modèles

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