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Fundamentals of Thermal Conductivity Measurement via ASTM 5470

Fundamentals of Thermal Conductivity Measurement via ASTM 5470. by Dr. John W. Sofia. Analysis Tech Inc. 2016. Definition of Apparent Thermal Conductivity. ASTM 5470 is Ohms law applied to one-dimensional heat flow.

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Fundamentals of Thermal Conductivity Measurement via ASTM 5470

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  1. Fundamentals of Thermal Conductivity Measurement via ASTM 5470 by Dr. John W. Sofia Analysis Tech Inc. 2016 Fundamentals www.analysistech.com

  2. Definition of Apparent Thermal Conductivity ASTM 5470 is Ohms law applied to one-dimensional heat flow. Conductivity defined only for heat flow between parallel, isothermal surfaces (ASTM 5470) Fundamentals www.analysistech.com

  3. Apparent versus Actual Thermal Conductivity Hot Test Surface Q Contact Resistance = Rt Sample L Q Q Contact Resistance = Rb Cold Test Surface kactual = kappIf Rt & Rb = 0 Actual conductivity of sample equals apparent conductivity only if contact resistances are zero Fundamentals www.analysistech.com

  4. Best Method for Conductivity Measurement - best-fit data line - RA Intercept = (Rt + Rb)*A Sample Thickness Fundamentals www.analysistech.com

  5. Best Method for Conductivity MeasurementRequirements: • Sum of Contact resistances must be the same for all samples (stacked samples have higher total contact resistance) • Fractional composition must be the same all samples (supporting matrices or meshes cause problems here) • Variable thicknesses must have uniform bulk properties (fabrication can yield thickness-dependent properties) Fundamentals www.analysistech.com

  6. Test Error: Failure to Use Constant Pressure (Type 2 Material) Fundamentals www.analysistech.com

  7. Contact Impedance Versus Pressure (Type 3 material, hard rubber, dry contact) Fundamentals www.analysistech.com

  8. Characteristics of Surface Contact Resistances Fundamentals www.analysistech.com

  9. Treating Surface Contact Resistances Fundamentals www.analysistech.com

  10. Type 1 Samples (ASTM 5470) Fundamentals www.analysistech.com

  11. Best Method for Conductivity Measurement(Type 1 Materials) Fundamentals www.analysistech.com

  12. Testing of Thin Type I Samples(“bond-line” testing) Hot Test Surface Q Top-Contact Rt Sample L Q • For small L, uncertainty, ε, dominates Rsamp measurement. • For small L and large k, Rsamp is small: yields low delta T and poor measurement accuracy • Hidden information about the test surfaces dominates RA Q BottomContact Rb Cold Test Surface Fundamentals www.analysistech.com

  13. Difficulties with Thin Type I Sample Testing Fundamentals www.analysistech.com

  14. Type 2 Samples (ASTM 5470) Fundamentals www.analysistech.com

  15. Best Method for Conductivity Measurement(Type 2 Materials) Fundamentals www.analysistech.com

  16. Type 3 Samples (ASTM 5470) Fundamentals www.analysistech.com

  17. Best Method for Conductivity Measurement(Type 3 Materials) Fundamentals www.analysistech.com

  18. Dependencies Δ-temperature across sample (low RA) Heat flow measurement (high RA) Environment temperature stability Impedance variation with time Sample area measurement & mounting Accuracy of TIM Measurements Thickness measurement accuracy TIM Tester Training www.analysistech.com

  19. Repeatability of TIM Measurements Fundamentals www.analysistech.com

  20. TIM Tester Pressure Range Options • Kit 1: 5 to 95 psi (60 to 650 kPa) +/- 3 psi • Kit 2: 10 to 170 psi (100-1100 kPa) +/- 5 psi • Kit 3: 10 to 380 psi (100-2600 kPa) +/- 10 psi • Kit 3: recommended for mostly type 3 materials • Kits 1 & 2: recommended for mostly type 1 & 2 materials • Pressure accuracy is +/-2.7% of maximum pressure • Kits can be changed by end-user and are available in complete set of 3 kits. Fundamentals www.analysistech.com

  21. Fundamentals www.analysistech.com

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