Thermal Conductivity - ASTM C177
The rate of heat flow through a material per unit thickness per degree of temperature difference across the thickness.
Testing is performed using a guarded-hot-plate apparatus. Two identical samples are placed on opposite sides of the main heater. The main heater and guard heaters are kept at the same temperature. Both auxiliary heaters are maintained a lower temperature. The guard heaters minimize the amount of lateral heat transfer from the main heater. Temperatures are monitored at each surface by thermocouples. The heat transferred through the specimens is equal to the power supplied to the main heater. Thermal equilibrium is established when temperature and voltage readings are steady.
Thermal conductivity is calculated using:
k = P / [t * (Tm - Ta)]
where P is the power supplied to the main heater,
t is the total specimen thickness (twice the single specimen thickness),
and Tm is the temperature of the main heater,
and Ta is the temperature of the auxiliary heater.