Thermal effusivity

In thermodynamics, the thermal effusivity, thermal inertia or thermal responsivity of a material is defined as the square root of the product of the material's thermal conductivity and its volumetric heat capacity.[1][2]

Thermal Effusivity Sensor
Thermal effusivity sensor typically used in the direct measurement of materials.

Here, is the thermal conductivity, is the density and is the specific heat capacity. The product of and 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[i] bodies initially at temperatures and are brought in perfect thermal contact, the temperature at the contact surface will be given by their relative effusivities.[3]

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 may be performed using specialty sensors, as pictured.

See alsoEdit


  1. ^ i.e. their thermal capacity is sufficiently large that their temperatures will not change measurably owing to this heat transfer
  1. ^ A reference defining various thermal properties[dead link]
  2. ^ Williams, F. A. (2009). "Simplified theory for ignition times of hypergolic gelled propellants". J. Propulsion and Power. 25 (6): 1354–1357. doi:10.2514/1.46531.
  3. ^ Baehr, H.D.; Stephan, K. (2004). Wärme- und Stoffübertragung 4. Auflage. Springer. p. 172. doi:10.1007/978-3-662-10833-8. ISBN 978-3-662-10834-5.

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