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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]].<ref>http://www.evitherm.org/default.asp?ID=277</ref> | |||
:<math>e = {(k\rho c_p)}^{1/2}</math> | |||
Here, '''k''' is the thermal conductivity, '''<math>\rho</math>''' is the [[density]] and '''<math>c_p</math>''' is the [[specific heat capacity]]. The product of '''<math>\rho</math>''' and '''<math>c_p</math>''' 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 '''T<sub>1</sub>''' and '''T<sub>2</sub>''' are brought in perfect thermal contact, the temperature at the contact surface '''T<sub>m</sub>''' will be given by their relative effusivities. <ref>H. D. Baehr and K. Stephan, ''Wärme- und Stoffübertragung 4. Auflage'', Springer, (2004), p 172, ISBN 3-540-40130-X </ref> | |||
:<math>T_m = T_1 + (T_2-T_1){e_2 \over (e_2+e_1)}</math> | |||
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|laser flash analysis]] | |||
* [[specific heat capacity]] | |||
* [[thermal conductivity]] | |||
* [[thermal diffusivity]] | |||
* [[thermal inertia]] | |||
==References== | |||
<references /> | |||
==External links== | |||
* [http://www.evitherm.org/default.asp?ID=277 A reference defining various thermal properties] | |||
* [http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatra.html Thermal heat transfer on HyperPhysics site] | |||
[[Category:Thermodynamics]] | |||
[[Category:Physical quantities]] | |||
[[Category:Heat conduction]] |
Revision as of 02:06, 4 February 2014
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]
Here, k 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 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. [2]
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
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