Eqs. (3)±(9) may be solved analytically or numerically.
Exact analytical solutions are in the form of in®-
nite series. Due to the complexities involved in obtain
exact solutions, the in®nite series is often approximated
to a single series term by assuming that the Fourier
number (Eq. (10)) is greater than 0.2 (Incropera & De-
Witt, 1996).