where, Hr is the air relative humidity (%), T is the air
temperature (K) and R is the gas constant (8.314 J/mol.K).
For long drying periods, Eq. (10) can be further simplified
to include only the first term of the series. Effective moisture
diffusivity is obtained by plotting the experimental drying data
in terms of ln(MR) versus time. From Eq. (12), a plot of
ln(MR) versus time gives a straight line with a slope of (S),
in which: