Saint-Gobain employs two standard thermal conductivity/thermal resistance test methods.
ASTM E1530
One is the guarded heat flow meter method, which conforms to ASTM E1530 (Diagram 3) and is mostly applicable to samples that range in thickness from 0.5 – 25mm. In this method an even reproducible pressure is applied to the test sample by pneumatic cylinders that allow test pressures ranging from 0 psi (contact) to 300 psi. The sample is held between two polished metal surfaces where the upper plate is heated and the lower plate is chilled, establishing a temperature gradient through the stack. The lower plate is also part of a calibrated heat flux transducer (HFT), as depicted in Diagram 3. Thermal conductivity can be determined by measuring the temperature resistance across the sample and using the output from the heat flux transducer according to the following general equations:
R = [(TU -TM)/Q] - Rint where:
R — thermal resistance
TU —upper plate surface temperature
TM — lower plate surface temperature
Q — heat flux through the test sample
Rint — total interface resistance between sample and surface plates
Q = N(TM-TL) where:
N — HFT (heat transfer coefficient)
TM — lower plate surface temperature
TL —bottom heater temperature
and subsequently,
R=d/C where:
d — sample thickness
C -— thermal conductivity
ASTM D5470
The other testing method is for thermal transmission properties of thin thermally conductive electrically insulating materials, which conforms to ASTM D5470 and is applicable to samples ranging in thickness from 0.02 – 10mm. In this method an even reproducible pressure is applied to the test sample by pneumatic cylinders that allow test pressures ranging from 0 psi (contact) to 500 psi. The sample is held between two polished metal surfaces where the lower plate is heated and the upper plate is chilled, establishing a temperature gradient through the stack that is measured via 4 thermocouples, as depicted on Diagram 4. Thermal impedance can be determined by measuring the temperature resistance across the sample according to the following general equations:
Q = V x I where:
Q — heat flow, W
V — electrical potential applied to the heater, V
I — electrical current flow in the heater, A
Temperature of the upper meter block is defined as:
TA = T2 – (dB/dA)(T1-T2) where:
TA — temperature of the upper
meter block surface in contact with
the specimen, K
T1— upper temperature of the upper meter block, K
T2— lower temperature of the upper meter block, K
dA — distance between temperature
sensors, m
dB — distance from the lower sensor to the lower surface of the upper meter block,
Temperature of the lower meter block is defined as:
TD = T3 – (dD/dC)(T3–T4) where:
TD — temperature of the lower
meter block surface in contact with
the specimen, K
T3—upper temperature of the lower meter block, K
T4 — lower temperature of the lower meter block, K
dC — distance between temperature
sensors, m
dD — distance from the upper sensor to the upper surface of the lower meter block, m
Thermal impedance can be calculated:
Θ = (TA - TD) x A/Q
To obtain thermal conductivity a plot of thermal impedance (y-axis) versus various sample thicknesses is generated. The slope of the straight line is the reciprocal of thermal conductivity. The y-intercept is the interfacial thermal resistance, which is dependent on clamping force and surface.