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
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.
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.