Thermal conductivity relates to the "quantity of heat" transmitted through a unit length per unit area in a unit of time. The units of thermal conductivity are watts per meter (M) per degree Kelvin (K) written as watts/M.K. Heat being a form of energy, the "quantity of heat" is measured in watts, just like electricity. Expressed as an equation: Thermal Conductivity = Watts times Distance divided by (area times temperature change). Standard Test Methods (STM) for measuring the thermal conductivity of solids, liquids, electrical and insulating materials and even soil have been developed.
One of the most versatile thermal conductivity instruments is the system manufactured by ThermTest Inc. Called the TPS 2500 S, it also can measure thermal diffusivity and specific heat to an accuracy better than 5 percent and a reproducibility better than 1 percent. It can measure thermal conductivity from 0.005 W/mK to 500 W/mK from cryogenic temperatures up to 750 degrees Celsius. The TPS 2500 S meets the international Standards Organization (ISO) standard for thermal conductivity called ISO/DIS 220007-2.2 . The TPS 2500 S can measure the thermal conductivity of solids, liquids, paste and powders.
The TPS 1500, also manufactured by ThermTest Inc., is a thermal conductivity instrument with versatile applications and ranges of operation. It can measure thermal conductivity from 0.1 to 400 W/mk and thermal diffusivity from 0.1 to 100 mm2/s.This thermal conductivity instrument applies, too, to solids, liquids, pastes and powders with cylindrical sample sizes as small as 0.01mm high and 2mm in diameter. Accuracy is better than 5 percent with reproducibility within 1 percent. The TPS 1500 meets the ISO/DIS 220007-2.2 standard for thermal conductivity tests.
The Hot Disc TPS 500 can measure thermal conductivity, thermal diffusivity and specific heat capacity of pastes, solids and low-viscosity liquids down to -100 degrees Celsius and up to 200 degrees Celsius. It comes with software that allows test results to be processed by Microsoft's Excel. It measures thermal conductivity within the range of 0.03 to 100 W/mK, thermal diffusivity from 0.02 to 40 mm2/s and specific heat capacity from 0.10 to 4.5 MJ/m3K. It is designed to meet the ISO standard ISO/DIS 22007-2:2008. It has the same level of accuracy and reproducibility of TPS 2500 and TPS 1500.