Thermal gradient estimation using rainbow thermometry

1. MUSCLES meeting Karlsruhe, September 21 2004 Thermal gradient estimation using rainbow thermometry • ONERA Research team • Nicolás GARCIA ROSAYves BISCOSGérard LAVERGNE

2. PRESENTATION OUTLINE • Experimental device • Temperature measurements • Objectives • Theoretical aspects • Solving methods • Thermal gradient estimations : examples

3. EXPERIMENTAL DEVICE • Monodisperse injector ; • Argon laser (514,5 nm) ; • Rainbow system ; • LIF system ; • Shadowgraphy.

4. LIF AND RAINBOW MEASUREMENTS

5. LIF AND RAINBOW MEASUREMENTS Ignitor

6. Improvement of the rainbow technique :OBJECTIVES • Correction of temperature measurement ; • Estimation of thermal gradients ; average temperature of a heating droplet LIF : gradient-insensitive measurement Two solving methods considerable thermal gradients during heating phase

7. evaporation model : AVAILABLE TOOLS theoretical models expected spherical temperature profile Generalized Lorenz-Mie theory (GLMT)-based calculations simple correlation Measurements from experimental device scattered intensity

8. LIGHT SCATTERING AROUND DROPLET correlations used

9. THEORETICAL ASPECTS Geometrical optics • Geometrical optics ; • Airy-Walker theory ; • Lorenz-Mie theory ; • Generalized Lorenz-Mie theory. Lorenz-Mie theory Generalized Lorenz-Mie theory Gaussian, off-axis laser beam

10. COMBINING THE DIFFERENT TOOLS

11. SOLUTION OF THE SYSTEM

12. RECALL OF THE TWO SOLVING METHODS

13. SIMULTANEOUS MEASUREMENT of MEAN TEMPERATURE and THERMAL GRADIENT • 2p-periodicity :multiple solutions !

14. GRADIENT ESTIMATIONS : evaporating droplets Airy-Walker classical rainbow inversion LIF measurement Airy-Walker classical rainbow inversion set-up Rainbow/LIF estimation

15. GRADIENT ESTIMATIONS : burning droplets Airy-Walker classical rainbow inversion set-up LIF measurement Airy-Walker classical rainbow inversion Rainbow/LIF estimation

16. CONCLUSIONS, PERSPECTIVES • New correlation obtained from the fringe pattern phase in forward direction. • The coupling LIF / Rainbow gives a good evaluation of the thermal gradients, especially in burning regime. • The second order rainbow provided no additional information. • Some problems must be resolved to get simultaneously the mean temperature and the thermal gradients from the above refractometry technique. • Actually the coupling of the two techniques : Infrared and Rainbow is going on. • The obtention of the surface temperature by infrared method will be another important information to be used for the validation of thermal gradients measurement.

17. IR MEASUREMENT IR thermal flux IR detector T°cn Planck ‘s law Black body spectral energy with : h = Planck’s constant = 6.6262 10 k = Boltzmann’s constant = 1.3806 10 m.s 8 -1 c = Light speed = 2.9979 10 Thermal flux emission in the IR range Black body en [W.Sr-1.m-3] J.K -34 -1 J.K -23 -1 Real body brightness

18. MESUREMENT TECHNIQUE : SIGNAL SHUT-OFF METHOD Voltage Droplet stream IR detector Droplet signal ( Tgoutte > Tcn ) Period T DV=0 => equal fluxes Period T Black body Time IR signal injector + non-intrusive + no calibration needed + correction of the system’s non-linearities - droplet position / time relation Blackbody signal

19. SPECTRAL BAND SELECTION :MEASUREMENT PROCESS Ethanol droplets D f 1 = DTEB . 1 g l p q ( , T ) 2 Ad . sin 0 0,9 0,8 ¶ ( ( ) ) ò g l = e l l l l * ( , T ) ( ). D ( ). L , T . d 0,7 goutte BLIP goutte ¶ T D l 0,6 Droplet emissivity Emissivity 0,5 0,4 Detector 10.13 spectral reponse 0,3 0,2 0,1 0 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Wavelength (µm) DTEB Emissivity Field of view Emissivity calculated by Mie theory Ambient Lens aperture Droplet Sensor (Ad) Lens Cold filter [K] with : merit factor 1E+10 Band 3-5 microns Band 8-12 microns Dl g 1E+9 1E+8 270 280 290 300 310 320 330 Droplets temperature (K)