Hot wire measurement method based on inverse method

1. Presented by Matthieu THOMAS PhD thesis: Airbus/LTN Hot wire measurement method based on inverse method SFT – Airbus meeting Monolithic composites thermal characterisation Round Robin Test May 19, 2005 Toulouse

2. First part Hot wire measurement technique Mai 2005 Round Robin test

3. z y hot wire x Temperature response measurement General description 4 Coupons of polymer reinforced with fibres aligned along x-direction Heating step Thermocouples z x Insulation Thermo-regulated plate Instrumented sample Time 120mm Temperature

4. General description Advantages • Estimation simultaneously of 3 parameters • Alternative method for Cp measurement • Effective power dissipated in the sample is known and controlled Drawbacks • Restricted to materials with low thermal conductivity • Instrumentation of the sample Power dissipated by the hot wire (U,I) + Temperature rises in the plane (x,z) x z ρcp Identification process

5. Insulation, Grease Measurement temperature q0 … Experimental data Numerical solver Analytical solver Conductances (h1, h2) Semi-infinite time (Tmax) Calculated temperatures Measured temperatures x z ρCp xi zi ρCpi Comparison Inverse method (Nelder Mead) RMS Initial parameters (x0, z0, ρCp0) Criteria of calculations ending Exactness location of the thermocouples Identification process

6. Residuals (°C) Practical case Thermo n°3 Thermo n°2 Thermo n°5 Thermo n°1 Measurement noise: 0.0091244°C RMS of residuals: 0.015097°C  Mean of the residuals  zero  Systematic error / Bias  Uncertainty on the thermocouples locations?

7. Measurement discrepancy - Future improvements Repeatability test campaign • Dispersion dues to experimental conditions < 3% • Uncertainty on the thermocouples locations < 2% Improvements • Realise a sensitivity analysis • Take into account the thermocouples location uncertainty • Measure the heat losses  Better known of limit conditions

8. Second part Experimental results Mai 2005 Round Robin test

9. REPEATABILITY 5 measurements per temperature Dispersion of the measurement method Measurements realised • x, z,ρCp • 25°, 40°, 60°, 95°C • Sample dimension: 120mm*120mm • Temperature imposed by thermo-regulated plates Hot wire technique

10. Mean value 5% Thermal conductivity along fibres direction : x • Dispersion  5%

11. Mean value 5% Transverse thermal conductivity : z

12. Mean value 5% Specific heat Cp

13. Conclusion - Comments • Hot wire measurement method provides two thermal conductivities and the specific heat • Measurement dispersion  5%