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.[1]
![Thermal Effusivity Sensor](http://upload.wikimedia.org/wikipedia/commons/thumb/e/e7/EffusivitySensor.jpg/220px-EffusivitySensor.jpg)
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.
Direct measurement of thermal effusivity may be performed via specialty sensors, as pictured to the right.
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