Nomenclature [C.sub.p] : Specific heat [h.sub.1] : Thickness of top melinex layer [h.sub.2] : Thickness of dye-coat layer [r.sub.0] : Radial length scale of laser beam [alpha] : A typical
thermal diffusivity t : Time t': Time at which heat source generated G : Instantaneous heat source solution T : Temperature [rho] : Density [T.sub.A] : Initial temperature [tau] : Time (t - t') v : Speed of laser beam [W.sub.0] : Wattage of laser [micro] : Optical density [lambda] : [micro] ln 10.
The time t it takes until the heat flow is stationary can be estimated by Equation 2, where a is the
thermal diffusivity (Eq.
In Figures 10 and 11 the borehole wall temperatures for the four cases investigated are shown as a function of the natural logarithm of Fourier number (Fo = a[tau]/[r.sup.2]), calculated by making use of the
thermal diffusivity of the ground and the borehole radius.
The footer is uninsulated and is treated as having the same properties as the surrounding ground because the
thermal diffusivity of concrete is similar enough to ground (approximately 7 x [10.sup.-7] [m.sup.2]/s [75 x [10.sup.-7] [ft.sup.2]/s]).
Also we consider how the heat generation in solid alters the behavior of temperature gradients in the different values of conductivity and
thermal diffusivity ratio.
2-4 we show temperature fields that we simulated by under the following conditions: Initial temperature of the plate: 130[degrees]C Ambient temperature: 18[degrees]C Thickness of first layer: 25 mm Thickness of second layer: 20 mm
Thermal diffusivity of first layer : 1.5 x [10.sup.-6] [m.sup.2] x [s.sup.-1]
Thermal diffusivity of second layer: 5.2 x [10.sup.-6] [m.sup.2] x [s.sup.-1]
where [P.sub.r], G, S, [E.sub.c], M, K and [k.sub.1] are respectively the Prandtl number, Grashof number, Sink strength, Eckert number, Hartmann number, co-efficient of
thermal diffusivity and non-Newtonian parameter.
Thermal diffusivity is a combination of the thermal conductivity divided by the specific weight and specific heat.
*
Thermal diffusivity ([alpha]') (measured at the temperature ([T.sub.p']+[T.sub.c])/2)
Specific heat capacity, along with
thermal diffusivity and density, are used to calculate thermal conductivity.
Temperature, thermal conductivity, specific heat capacity and
thermal diffusivity can all be measured quickly and easily using the Decagon KD2 thermal properties meter.
The
thermal diffusivity of the mashed potato decreased with increasing fat levels and increased with increasing salt levels.