# Thermal diffusivity

Thermal diffusivity

In heat transfer analysis, thermal diffusivity (symbol: $alpha,$, but note that the symbols $kappa$, $D$, and $k$ are all commonly used) is the ratio of thermal conductivity to volumetric heat capacity. It has SI of m²/s.

:$alpha = \left\{k over \left\{ ho c_p$

where:
* $k$ : thermal conductivity (SI units: W/m·K)
* $ho$ : density (kg/m³)
* $c_p$ : specific heat capacity (J/kg·K)

The denominator of the thermal diffusivity expression above, $ho c_p,$, can be identified as the volumetric heat capacity with SI units of J/m³·K.

Substances with high thermal diffusivity rapidly adjust their temperature to that of their surroundings, because they conduct heat quickly in comparison to their volumetric heat capacity or 'thermal bulk'.

ee also

* Thermodiffusion
* Heat capacity
* Specific heat capacity
* Heat equation
* Thermal conductivity
* Thermal effusivity
* Thermal time constant
* A [http://users.wpi.edu/~ierardi/PDF/air_alpha_plot.PDF plot of thermal diffusivity versus temperature for air] ("James Ierardi's Fire Protection Engineering Site").

References

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### Look at other dictionaries:

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