Understanding Different Thermal Conductivity Techniques

Thermal analysis and the resulting data can provide invaluable information to researchers and manufacturers in many sectors in the development advancement of new materials. However, before the introduction of C-Therm's patented approach, traditional technologies for such analysis have been expensive and/or destructive, as well as very time consuming in both sample preparation and testing.

This section will briefly explain and compare several techniques for measuring thermal conductivity, including the modified transient plane source technology developed by C-Therm. 

For an at-a-glance comparison of the various methods, click here.

	Guarded Hot Plate This steady state technique involves placing a solid sample of fixed dimension between two temperature-controlled plates. One plate is heated while the other plate is cooled, and their temperatures are monitored until they are constant. The steady state temperatures, the thickness of the sample and the heat input are used to calculate the thermal conductivity.
	Hot Wire This transient technique involves placing an electrically heated wire into a material. This intrusive method is limited to testing foams, fluids and melted plastics. The heat flows out radially from the wire into the sample and the temperature of the wire is measured. By plotting the temperature of the wire versus the logarithm of time, thermal conductivity can be calculated.
	Modified Transient Plane Source Technique (TCi Sensor) Developed by C-Therm (formerly Mathis Instruments), this approach is a transient technique that uses heat reflectance, similar to Hot Wire testing. The modification is that the heating element is supported on a backing, thus allowing a one-directional heat flow. This allows the testing to be non-intrusive and permits the testing of solids without the need to be melted. Therefore, the temperature of the heating element versus the time function is used to calculate the thermal conductivity and thermal effusivity.
	Laser Flash Diffusivity This is a transient method in which a short pulse of heat, supplied by a laser flash, is applied to the front face of a sample. On the rear face of the sample, an infrared (IR) detector is used to measure the temperature change. This temperature data is monitored as a function of time and used to determine thermal diffusivity. If the density and heat capacity of the sample are also known, the thermal conductivity can be calculated.