Transient Line Source (TLS) Technique
Principles of Operation
The C-Therm TCi Thermal Conductivity Analyzer Needle configuration employs the Transient Line Source technique in characterizing the thermal conductivity of materials. The TLS sensors operate in accordance with several industry standards including ASTM D5334, D5930 and IEEE Std 442-1981. Commonly referred to as “needle probes”, The TLS sensors provide a robust and efficient solution for measuring the thermal conductivity of granular materials, powders, polymer melts, soils, slurries, gels, and pastes.
This technique involves placing an electrically heated needle into a material. The heat flows out radially from the needle into the sample. During heating, the temperature difference between a thermocouple (T1) positioned in the middle of the heating wire, and a second thermocouple (T2) located at the tip of the needle is measured. By plotting this temperature difference versus the logarithm of time, thermal conductivity can be calculated. Typically, the measurement is on the order of 2-10 minutes.
The TLS module can be offered as a stand-alone product or can be bundled together with C-Therm’s other sensor capabilities for maximum versatility in thermal conductivity characterization.
How it Works
(1) A known amount of heat is applied to the heater wire of the sensor, providing a known amount of heat per unit length.
(2) The applied current results in an increase in temperature in the heating zone, which is measured using a pair of thermocouples (at T1 and T2).
(3) The rate of increase in temperature as a function of logarithmic time then gives the thermal conductivity of the sample. The slope of the line is inversely proportional to the rate of temperature increase at the heated zone of the sensor. Temperature will rise more steeply when lower thermal conductivity materials (e.g. powders) are tested. Conversely, the slope will be flatter for higher thermal conductivity materials (e.g. carbon polymer composite melts). C-Therm’s software allows two-click data analysis making thermal conductivity measurement fast and easy.