where u = t - [tau], [gamma] = [r.sup.2.sub.0]/([r.sup.2.sub.0] + 4[alpha]u), [alpha] is the
thermal diffusivity, [rho] is the density, and cp is the specific heat.
Our results as presented in Figure 7 show that the bark-based insulation boards produced do not have a very low thermal conductivity but do have comparatively low
thermal diffusivity values and could therefore be well suited for heat storage-optimized insulation materials for buildings.
As can be seen from Figures 10 and 11, this effect decreases when the ratio between the
thermal diffusivity of the grout and that of the ground increases; this ratio is 0.27 for BG and 0.93 for TEG.
While concrete may have a cold "feel" as do other masonry floors due to its
thermal diffusivity, it is not cold.
SigmaSoft, for instance, accepts thermal conductivity data and, in conjunction with specific heat capacity and density, calculates
thermal diffusivity.
Heat dissipation graphite sheets are used for small electronic devices, such as smartphones and tablet terminals, which are devices becoming dramatically popular in recent years, for their high
thermal diffusivity. However, no standard for methods to simply calculate the
thermal diffusivity of such sheets had been stipulated.
To characterize the rapidity of heat propagation through the composite, the
thermal diffusivity coefficient of the composite was measured using a LFA 457 laser flash apparatus.
The Rayleigh number (Ra) is defined as the product of the Grashof number (Gr), which describes the relationship between buoyancy and viscosity within a fluid, and the Prandtl number (Pr), which describes the relationship between momentum diffusivity and
thermal diffusivity. For free convection near a vertical wall, this number is defined as follows:
In a laser flash
thermal diffusivity test, a small specimen is subjected to a quick, intense radiant laser pulse after thermal equilibration at the test temperature of interest.
where [G.sub.Fo] is the analytical solution, also known as the G-factor, [F.sub.o] is the Fourier number defined as [F.sub.o]=4[alpha]t/[d.sup.2], a is the ground
thermal diffusivity, d is the borehole diameter, and k is the ground thermal conductivity.
Thermal diffusivity is defined as the thermal conductivity divided by the specific heat and density.
Diamond-like carbon (DLC) possesses high thermal conductivity,
thermal diffusivity, and thermal radiation; furthermore, the coefficient of thermal expansion (CTE) of DLC is similar to that of GaN.
