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Thermal diffusivity
 
 
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In heat transfer
Heat transfer

Heat transfer is the transition of thermal energy or simply heat from a hotter object to a cooler object . When an object or fluid is at a different temperature than its thermodynamic system or another object, transfer of thermal energy, also known as heat transfer, or heat exchange, occurs in such a way that the body and the surround...
 analysis, thermal diffusivity (symbol: , but note that the symbols , , and are all commonly used) is the ratio of thermal conductivity
Thermal conductivity

In physics, thermal conductivity, , is the List of materials properties of a material that indicates its ability to conduct heat. It appears primarily in Heat conduction#Fourier's law for heat conduction....
 to volumetric heat capacity
Volumetric heat capacity

Volumetric 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....
. It has the SI
Si

Si, si, or SI may refer to :...
 unit of m²/s.








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In heat transfer
Heat transfer

Heat transfer is the transition of thermal energy or simply heat from a hotter object to a cooler object . When an object or fluid is at a different temperature than its thermodynamic system or another object, transfer of thermal energy, also known as heat transfer, or heat exchange, occurs in such a way that the body and the surround...
 analysis, thermal diffusivity (symbol: , but note that the symbols , , and are all commonly used) is the ratio of thermal conductivity
Thermal conductivity

In physics, thermal conductivity, , is the List of materials properties of a material that indicates its ability to conduct heat. It appears primarily in Heat conduction#Fourier's law for heat conduction....
 to volumetric heat capacity
Volumetric heat capacity

Volumetric 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....
. It has the SI
Si

Si, si, or SI may refer to :...
 unit of m²/s.

where:
  • : thermal conductivity
    Thermal conductivity

    In physics, thermal conductivity, , is the List of materials properties of a material that indicates its ability to conduct heat. It appears primarily in Heat conduction#Fourier's law for heat conduction....
     (SI
    Si

    Si, si, or SI may refer to :...
     units: W/(m·K))
  • : density
    Density

    The density of a material is defined as its mass per unit volume. The symbol of density is ....
     (kg/m³)
  • : specific heat capacity
    Specific heat capacity

    Specific heat capacity, also known simply as specific heat, is the measure of the energy required to increase the temperature of a of a substance by a certain Celsius#Temperatures_and_intervals....
     (J/(kg·K))


The denominator of the thermal diffusivity expression above, , can be identified as the volumetric heat capacity
Volumetric heat capacity

Volumetric 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....
 with the SI
Si

Si, si, or SI may refer to :...
 unit of J/(m³·K).

Substances with high thermal diffusivity rapidly adjust their temperature to that of their surroundings, because they conduct heat quickly in comparison to their volumetric heat capacity or 'thermal bulk'.

Some thermal diffusivities of common materials
Material Thermal diffusivity
m²/s
Aluminium 8.418 × 10-5
Carbon steel (1%) 1.172 × 10-5
Copper 1.1234 × 10-4
Pure silver (99.9%) 1.6563 × 10-4
Aluminium oxide (polycrystalline) 1.20 × 10-5
Common brick 5.2 × 10-7
Pyrolytic graphite, parallel to layers 1.22 × 10-3
Pyrolytic graphite, normal to layers 3.6 × 10-6
Window glass 3.4 × 10-7
Nylon 9 × 10-8
Sandstone 1.12 × 10-6 to 1.19 × 10-6
Wood (Yellow Pine) 8.2 × 10-8
Air (1 atm, 300 K) 2.2160 × 10-5
Water vapour (1 atm, 400 K) 2.338 × 10-5
Engine oil (saturated liquid, 100 °C) 7.38 × 10-8
Rubber 1.3 × 10-7


See also


  • Thermodiffusion
  • Heat capacity
  • Specific heat capacity
    Specific heat capacity

    Specific heat capacity, also known simply as specific heat, is the measure of the energy required to increase the temperature of a of a substance by a certain Celsius#Temperatures_and_intervals....
  • 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. For a function u of three spatial variables and the time variable t, the heat equation is...
  • Thermal conductivity
    Thermal conductivity

    In physics, thermal conductivity, , is the List of materials properties of a material that indicates its ability to conduct heat. It appears primarily in Heat conduction#Fourier's law for heat conduction....
  • Thermal effusivity
    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....
  • Thermal time constant
  • A (James Ierardi's Fire Protection Engineering Site).
  • A .