where a¼/Cp is the thermal diffusivity. The quantity (2at)1/2 has dimensions
of length and is a measure of the distance heat can diffuse in time t.
Equation (6.56) says that the most energy-efficient kiln wall is one that only
starts to get really hot on the outside as the firing cycle approaches completion.
Substituting equation (6.55) back into equation (6.55) to eliminate
w gives