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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.
α is the thermal diffusivity, D is the mass diffusivity, λ is the thermal conductivity, ρ is the density, D im is the mixture-averaged diffusion coefficient, c p is the specific heat capacity at constant pressure. In the field of fluid mechanics, many sources define the Lewis number to be the inverse of the above definition. [3] [4]
Chemical potential μ i: Pressure: p: Pa Volume V: Temperature: T: K Entropy S: Thermal conductivity: k: W/(m·K) Thermal diffusivity: α: m 2 /s Thermal expansion (linear) α L: K −1: Thermal expansion (area) α A: K −1: Thermal expansion (volumetric) α V: K −1: Vapor quality [2] χ – Volume: V: m 3: Pressure P Specific volume: ν: m ...
The Fourier number can be derived by nondimensionalizing the time-dependent diffusion equation. As an example, consider a rod of length L {\displaystyle L} that is being heated from an initial temperature T 0 {\displaystyle T_{0}} by imposing a heat source of temperature T L > T 0 {\displaystyle T_{L}>T_{0}} at time t = 0 {\displaystyle t=0 ...
This can be taken as a significant (and purely mathematical) justification of the use of the Laplacian and of the heat equation in modeling any physical phenomena which are homogeneous and isotropic, of which heat diffusion is a principal example. The diffusivity constant, α, is often not present in mathematical studies of the heat equation ...
There are some notable similarities in equations for momentum, energy, and mass transfer [7] which can all be transported by diffusion, as illustrated by the following examples: Mass: the spreading and dissipation of odors in air is an example of mass diffusion. Energy: the conduction of heat in a solid material is an example of heat diffusion.
The Maxwell–Stefan diffusion (or Stefan–Maxwell diffusion) is a model for describing diffusion in multicomponent systems. The equations that describe these transport processes have been developed independently and in parallel by James Clerk Maxwell [1] for dilute gases and Josef Stefan [2] for liquids. The Maxwell–Stefan equation is [3 ...
The higher the thermal diffusivity of the sample, the faster the energy reaches the backside. A laser flash apparatus (LFA) to measure thermal diffusivity over a broad temperature range, is shown on the right hand side. In a one-dimensional, adiabatic case the thermal diffusivity is calculated from this temperature rise as follows: