The theoretical relationship between heat flux and temperature gradient for homogeneous materials is well known and described by a Fourier equation. However, this relationship does not hold for nonhomogeneous materials such as porous-capillary bodies, cellular systems, suspensions, and pastes. An experiment was conducted to estimate the mean thermal relaxation time (defined as the mean time needed for accumulating the thermal energy required for propagative transfer of heat) for several nonhomogeneous materials (Journal of Heat Transfer, Aug. 1990). A 95% confidence interval for the mean thermal relaxation time of sand was found to be 20.2 ± 6.4 seconds.
a. Give a practical interpretation of the 95% confidence interval.
b. Give a theoretical interpretation of the 95% confidence interval.