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Thermal diffusivity is a contrasting measure to thermal effusivity. [6] [7] In a substance with high thermal diffusivity, heat moves rapidly through it because the substance conducts heat quickly relative to its volumetric heat capacity or 'thermal bulk'. Thermal diffusivity is often measured with the flash method.
The higher the thermal diffusivity of the sample, the faster the energy reaches the backside. A laser flash apparatus (LFA) to measure thermal diffusivity over a broad temperature range, is shown on the right hand side. In a one-dimensional, adiabatic case the thermal diffusivity is calculated from this temperature rise as follows:
1781 - Joseph Priestley attempts to measure the ability of different gases to conduct heat using the heated wire experiment. 1931 - Sven Pyk and Bertil Stalhane proposed the first “transient” hot wire method for the measurement of thermal conductivity of solids and powders. Unlike previous methods, the one devised by Pyk and Stalhane used ...
Here, Λ is the thermal conductivity of the solid, D is the thermal diffusivity of the solid, and r is the radial coordinate. In a typical time-domain thermoreflectance experiment, the co-aligned laser beams have cylindrical symmetry, therefore the Hankel transform can be used to simplify the computation of the convolution of the equation with ...
The heat generated dissipates into the sample on both sides of the sensor, at a rate depending on the thermal transport properties of the material. By recording temperature vs. time response in the sensor, the thermal conductivity, thermal diffusivity and specific heat capacity of the material can be calculated.
The thermal conductivity of a material is a measure of its ability to conduct heat.It is commonly denoted by , , or and is measured in W·m −1 ·K −1.. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity.
Small values of the Prandtl number, Pr ≪ 1, means the thermal diffusivity dominates. Whereas with large values, Pr ≫ 1, the momentum diffusivity dominates the behavior. For example, the listed value for liquid mercury indicates that the heat conduction is more significant compared to convection, so thermal diffusivity is dominant. However ...
The Lock-In method is suitable for testing components with a low thermal diffusivity and it has many modifications for various specific applications (such as Lock-In Ref, Lock-In Online, etc.). Pulse thermography (pulse method) [6]. A very short pulse – usually in the units of milliseconds – is used to excite the object. The cooling process ...