High Temperature Solid thermal conductivity cells

ITI Company: The Model C-2500-HTS Thermal Conductivity system is designed for measuring the thermal conductivities of highly conducting materials from room temperatures to 1000 °F. Sample dimensions are 2 1/4” diameter, and thickness range between 0.0005” to 1.000”.

THE HIGH TEMPERATURE, THERMAL CONDUCTIVITY MEASUREMENT TECHNIQUE

The contact (sensing) surfaces of the high temperature conductivity system are composed of traceable Alumel, whose thermoelectric and physical properties are known. A disc of Chromel, whose properties are also known as a function of temperature, is placed in thermal, and electrical contact between the Alumel surfaces. At a constant heat flow, a temperature difference will be established across the Chromel disc, consequently, a thermoelectric voltage will be generated between the Alumel surfaces. This voltage is directly related to the heat flux through the Alumel surface.

Two such heat flux sensors encompass the sample to be measured, thus, the heat flux entering the sample can be averaged with the heat flux exiting the sample. The values so obtained obviate the necessity for guarded hot plates, thus yielding greater accuracy.

The temperature difference across the sample is sensed with two Type “K” Chromel/Alumel thermocouple discs, which provide an average value over the entire sample surface.

When measuring highly conducting samples, the interface resistances between the sample surfaces and the sensing surfaces can be greater than the innate thermal resistance of the sample. A special technique has been developed to determine the actual surface temperatures of the sample and may be applied not only to high temperature conductivity measurements, but also to low temperature measurements.