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Thermal effusivity

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Thermal effusivity

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.

e = ( k ρ c p ) 1 / 2

Here, k is the thermal conductivity, ρ is the density and c p is the specific heat capacity. The product of ρ 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 Tm will be given by their relative effusivities.

T m = T 1 + ( T 2 T 1 ) e 2 ( 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.

Direct measurement of thermal effusivity be performed via specialty sensors, as pictured to the right.

References

Thermal effusivity Wikipedia


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