Thermal diffusivity

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In heat transfer analysis, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It measures the rate of transfer of heat of a material from the hot side to the cold side. It has the SI derived unit of m²/s. Thermal diffusivity is usually denoted ? but a, ?, K, and D are also used. The formula is:

${\displaystyle \alpha ={k \over {\rho c_{p}}}}$

where

• ${\displaystyle k}$ is thermal conductivity (W/(m·K))
• ${\displaystyle \rho }$ is density (kg/m³)
• ${\displaystyle c_{p}}$ is specific heat capacity (J/(kg·K))

Together, ${\displaystyle \rho c_{p}\,}$ can be considered the volumetric heat capacity (J/(m³·K)).

As seen in the heat equation,

${\displaystyle {\frac {\partial T}{\partial t}}=\alpha \nabla ^{2}T}$,

one way to view thermal diffusivity is as the ratio of the time derivative of temperature to its curvature, quantifying the rate at which temperature concavity is "smoothed out". In a sense, thermal diffusivity is the measure of thermal inertia. 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. It involves heating a strip or cylindrical sample with a short energy pulse at one end and analyzing the temperature change (reduction in amplitude and phase shift of the pulse) a short distance away.

Video Thermal diffusivity

See also

• Heat equation
• Laser flash analysis
• Thermodiffusion
• Thermal effusivity
• Thermal time constant

Maps Thermal diffusivity

References

Source of the article : Wikipedia