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Fundamentals of Thermal Conductivity Measurement via ASTM 5470. by Dr. John W. Sofia. Analysis Tech Inc. 2010. 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 by Dr. John W. Sofia Analysis Tech Inc. 2010 Fundamentals www.analysistech.com
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
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
Best Method for Conductivity Measurement - best-fit data line - RA Intercept = (Rt + Rb)*A Sample Thickness Fundamentals www.analysistech.com
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
Test Error: Failure to Use Constant Pressure (Type 2 Material) Fundamentals www.analysistech.com
Contact Impedance Versus Pressure (Type 3 material, hard rubber, dry contact) Fundamentals www.analysistech.com
Characteristics of Surface Contact Resistances Fundamentals www.analysistech.com
Treating Surface Contact Resistances Fundamentals www.analysistech.com
Type 1 Samples (ASTM 5470) Fundamentals www.analysistech.com
Best Method for Conductivity Measurement(Type 1 Materials) Fundamentals www.analysistech.com
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
Difficulties with Thin Type I Sample Testing Fundamentals www.analysistech.com
Type 2 Samples (ASTM 5470) Fundamentals www.analysistech.com
Best Method for Conductivity Measurement(Type 2 Materials) Fundamentals www.analysistech.com
Type 3 Samples (ASTM 5470) Fundamentals www.analysistech.com
Best Method for Conductivity Measurement(Type 3 Materials) Fundamentals www.analysistech.com
Repeatability of TIM Measurements Fundamentals www.analysistech.com
Accuracy of TIM Measurements Fundamentals www.analysistech.com
TIM Tester 1300, 1400 Features • Automatic operation under WinTIM Software • Electronic sample thickness measurement - "as-tested" • Sample-temperature control & batch testing • Automatic pressure control & batch testing • Controlled-thickness & controlled-pressure test modes • Automatic estimation of measurement accuracy • In-house calibration procedures • English or metric unit selection • Requires chiller, compressed air, & PC computer Fundamentals www.analysistech.com
TIM Tester 1300 Fundamentals www.analysistech.com
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