In heat transfer analysis, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure.[1] It is a measure of the rate of heat transfer inside a material. It has units of m2/s. Thermal diffusivity is usually denoted by lowercase alpha (α), but a, h, κ (kappa),[2]K,[3] and D are also used.
The formula is:[4]
where
k is thermal conductivity (W/(m·K))
cp is specific heat capacity (J/(kg·K))
ρ is density (kg/m3)
Together, ρcp can be considered the volumetric heat capacity (J/(m3·K)).
As seen in the heat equation,[5]
one way to view thermal diffusivity is as the ratio of the time derivative of temperature to its curvature, quantifying the rate at which temperature concavity is "smoothed out". Thermal diffusivity is a contrasting measure to thermal effusivity.[6][7] In a substance with high thermal diffusivity, heat moves rapidly through it because the substance conducts heat quickly relative to its volumetric heat capacity or 'thermal bulk'.
Thermal diffusivity is often measured with the flash method.[8][9] It involves heating a strip or cylindrical sample with a short energy pulse at one end and analyzing the temperature change (reduction in amplitude and phase shift of the pulse) a short distance away.[10][11]
^Lide, David R., ed. (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. p. 2-65. ISBN 978-1-4200-9084-0.
^Hetnarski, Richard B.; Eslami, M. Reza (2009). Thermal Stresses - Advanced Theory and Applications (Online-Ausg. ed.). Dordrecht: Springer Netherlands. p. 170. doi:10.1007/978-3-030-10436-8. ISBN 978-1-4020-9247-3.
^Unsworth, J.; Duarte, F. J. (1979), "Heat diffusion in a solid sphere and Fourier Theory", Am. J. Phys., 47 (11): 891–893, Bibcode:1979AmJPh..47..981U, doi:10.1119/1.11601
^Lightfoot, R. Byron Bird, Warren E. Stewart, Edwin N. (1960). Transport Phenomena. John Wiley and Sons, Inc. Eq. 8.1-7. ISBN 978-0-471-07392-5.{{cite book}}: CS1 maint: multiple names: authors list (link)
^Carslaw, H. S.; Jaeger, J. C. (1959), Conduction of Heat in Solids (2nd ed.), Oxford University Press, ISBN 978-0-19-853368-9
^Dante, Roberto C. (2016). Handbook of Friction Materials and Their Applications. Elsevier. pp. 123–134. doi:10.1016/B978-0-08-100619-1.00009-2.
^Venkanna, B.K. (2010). Fundamentals of Heat and Mass Transfer. New Delhi: PHI Learning. p. 38. ISBN 978-81-203-4031-2. Retrieved 1 December 2011.
^"NETZSCH-Gerätebau, Germany". Archived from the original on 2012-03-11. Retrieved 2012-03-12.
^
W.J. Parker; R.J. Jenkins; C.P. Butler; G.L. Abbott (1961). "Method of Determining Thermal Diffusivity, Heat Capacity and Thermal Conductivity". Journal of Applied Physics. 32 (9): 1679. Bibcode:1961JAP....32.1679P. doi:10.1063/1.1728417.
^
J. Blumm; J. Opfermann (2002). "Improvement of the mathematical modeling of flash measurements". High Temperatures – High Pressures. 34 (5): 515. doi:10.1068/htjr061.
^Thermitus, M.-A. (October 2010). "New Beam Size Correction for Thermal Diffusivity Measurement with the Flash Method". In Gaal, Daniela S.; Gaal, Peter S. (eds.). Thermal Conductivity 30/Thermal Expansion 18. 30th International Thermal Conductivity Conference/18th International Thermal Expansion Symposium. Lancaster, PA: DEStech Publications. p. 217. ISBN 978-1-60595-015-0. Retrieved 1 December 2011.
and 24 Related for: Thermal diffusivity information
is "smoothed out". Thermaldiffusivity is a contrasting measure to thermal effusivity. In a substance with high thermaldiffusivity, heat moves rapidly...
different mediums. Diffusivity may refer to: Thermaldiffusivity, diffusivity of heat Diffusivity of mass: Mass diffusivity, molecular diffusivity (often called...
ratio of momentum diffusivity to thermaldiffusivity. The Prandtl number is given as: P r = ν α = momentum diffusivitythermaldiffusivity = μ / ρ k / ( c...
z^{2}}}\right)} in which α is a positive coefficient called the thermaldiffusivity of the medium. In addition to other physical phenomena, this equation...
thermal transport properties of the material. By recording temperature vs. time response in the sensor, the thermal conductivity, thermaldiffusivity...
The laser flash analysis or laser flash method is used to measure thermaldiffusivity of a variety of different materials. An energy pulse heats one side...
) or as the ratio of thermal conductivity to the square root of thermaldiffusivity ( α {\displaystyle \alpha } ). e = λ α = ( λ ρ c p ) {\displaystyle...
(Pr), which describes the relationship between momentum diffusivity and thermaldiffusivity: Ra = Gr × Pr. Hence it may also be viewed as the ratio of...
track the thickness and shape of that portion of the thermal boundary layer where thermaldiffusivity α {\displaystyle {\alpha }} is significant. Hence the...
dimensionless number defined as the ratio of momentum diffusivity (kinematic viscosity) and mass diffusivity, and it is used to characterize fluid flows in which...
(insulation) Thermal transmittance Specific heat capacity Thermal conductivity Thermal conductivities of the elements (data page) Thermaldiffusivity Thermodynamics...
also related to thermaldiffusivity, heat capacity and insulation. Concrete has low thermaldiffusivity, high heat capacity, and its thermal mass is negatively...
used in the study of mass diffusion, in which the thermaldiffusivity is replaced by the mass diffusivity. The Fourier number is used in analysis of time-dependent...
that has been adapted for practical use in the form of thermal spraying. The thermaldiffusivity coefficient, represented as α {\displaystyle \alpha }...
main soil thermal properties are Volumetric heat capacity, SI Units: J∙m−3∙K−1 Thermal conductivity, SI Units: W∙m−1∙K−1 Thermaldiffusivity, SI Units:...
is dependent on only three properties of a chemical mixture: the thermaldiffusivity of the mixture, the reaction rate of the mixture and the temperature...
Diffusivity, mass diffusivity or diffusion coefficient is usually written as the proportionality constant between the molar flux due to molecular diffusion...
above, the equation is modified for thermal expansion and thermaldiffusivity. Density variations due to thermal expansion are given by: Δ ρ = ρ 0 β Δ...
^{2}T}{\partial ^{2}x'}}} where κ {\displaystyle \kappa } is the thermaldiffusivity of the mantle lithosphere. Since T depends on x' and t only through...
\Omega }}}} [citation needed] where α {\displaystyle \alpha } is the thermaldiffusivity of the material (m2s−1), Ω {\displaystyle \Omega } is the external...
supercritical carbon dioxide. Table of thermal and physical properties of saturated liquid carbon dioxide: Table of thermal and physical properties of carbon...
Global Information
