Measuring the Thermal Diffusivity
The rate at which a substance reacts to changes in temperature depends on its thermal conductivity, its density and its specific heat capacity. The thermal conductivity determines how quickly the heat spreads in a fabric. The specific heat capacity indicates how much of this heat is stored in the fabric. The density takes into account how much substance per cubic meter is present. These relationships are described by the thermal conductivity. This substance size is equal to the quotient of thermal conductivity and the product of specific heat capacity and density. From this formula, the unit of measure [m²/s] is calculated.
The thermal diffusivity is required for the assessment of heating and cooling processes, temperature changes in living spaces and thermal stresses in components. For example, the indicator is an important criterion in the classification of civil engineering equipment to prevent fire spread.
If a fast temperature compensation in materials is desired, materials with a high thermal conductivity are advantageous. These include metals and graphite. These substances are used for example in temperature measuring instruments and temperature controllers. Non-metals conduct the temperature significantly worse. They are suitable, among other things, for heat storage in regenerators.
For the measurement of the thermal diffusivity, a material sample is placed between two elements with constant, mutually different temperatures and the local and temporal temperature profile in the sample is evaluated. These elements can be found, for example, in the LINSEIS Heat Flow Meter. Precise measurement data for very thin layers is provided by our TF-LFA – LaserFlash for thin films, which works on the basis of laser beams. The Linseis gauges simultaneously determine the thermal conductivity, the thermal diffusivity and the specific heat capacity based on the included software.
Applications measuring thermal diffusivity
Application: Measuring Cermaic Filled Polymers using THB
Application: Isotropic graphite (AIST) using LFA
This graph shows the Thermal Diffusivity values measured on a LINSEIS LFA 1000 compared to the values measured at AIST* Japan. The literature values of the used Isotropic Graphite from AIST* the measured results on the LFA 1000 vary by less than 2 %.