Thermal effusivity

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In Thermodynamics, the thermal effusivity of a material is defined as the square root of the product of the material's thermal conductivity and its volumetric heat capacity.^[1]

$e={(k\rho c_{p})}^{{1/2}}$

Here, k is the thermal conductivity, $\rho$ is the density and $c_{p}$ is the specific heat capacity. The product of $\rho$ and $c_{p}$ is known as the volumetric heat capacity.

A material's thermal effusivity is a measure of its ability to exchange thermal energy with its surroundings.

If two semi-infinite bodies initially at temperatures T₁ and T₂ are brought in perfect thermal contact, the temperature at the contact surface T_m will be given by their relative effusivities. ^[2]

$T_{m}=T_{1}+(T_{2}-T_{1}){e_{2} \over (e_{2}+e_{1})}$

This expression is valid for all times for semi-infinite bodies in perfect thermal contact. It is also a good first guess for the initial contact temperature for finite bodies.

References

↑ http://www.evitherm.org/default.asp?ID=277
↑ H. D. Baehr and K. Stephan, Wärme- und Stoffübertragung 4. Auflage, Springer, (2004), p 172, ISBN 3-540-40130-X

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Thermal effusivity

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References

External links