The values of effective diffusivity obtained for mint at different
operating conditions as presented in Table 4 ranged between
1.2 · 1011 and 1.33 · 1011 m2 s1. It could be noticed that
the effective diffusivity values of forced convection runs were
higher than that of natural convection ones. The results are
in agreement with that found by Park et al. [7], where they reported
that the effective diffusivity is expressed as a function in air temperature and air velocity. They found that increasing of
drying air velocity from 0.5 m s1 to 1 m s1 at 50 C increased
the effective diffusivity of mint from 2.261 · 1012 to
2.945 · 1012 m2 s1, respectively. They related this increase
in the effective diffusivity to the effect of air velocity on reducing
the external resistance of mass transfer.