Differential graded category

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.

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

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.

$T_m=T_1+(T_2-T_1)\frac{e_2}{(e_2+e_1)}$

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.

See also

• heat capacity
• heat equation
• laser flash analysis
• specific heat capacity
• thermal conductivity
• thermal diffusivity
• thermal inertia

External links

• A reference defining various thermal properties
• Thermal heat transfer on HyperPhysics site