Thermal effusivity

In Thermodynamics

Thermodynamics

Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...

, the thermal effusivity of a material is defined as the square root of the product of the material's thermal conductivity

Thermal conductivity

In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

 and its volumetric heat capacity

Volumetric heat capacity

Volumetric heat capacity , also termed volume-specific heat capacity, describes the ability of a given volume of a substance to store internal energy while undergoing a given temperature change, but without undergoing a phase change...

.


Here, k is the thermal conductivity, is the density

Density

The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

 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

Thermal energy

Thermal energy is the part of the total internal energy of a thermodynamic system or sample of matter that results in the system's temperature....

 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.


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

• thermal inertia
• thermal diffusivity
  Thermal diffusivity
  In heat transfer analysis, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It has the SI unit of m²/s...
  
  
• heat capacity
  Heat capacity
  Heat capacity , or thermal capacity, is the measurable physical quantity that characterizes the amount of heat required to change a substance's temperature by a given amount...
  
  
• specific heat capacity
• heat equation
  Heat equation
  The heat equation is an important partial differential equation which describes the distribution of heat in a given region over time...
  
  
• thermal conductivity
  Thermal conductivity
  In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....
  
  

External links

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