The grain volume values for Sorkheh and Sazandegi
cultivars were 20.27 and 21.06mm3, respectively. Surface
area values for Sorkheh and Sazandegi were observed in
the ranges 25.62–37.28 and 26.3–38.46mm2, while mean
value were 31.76 and 32.58mm2, respectively. The
surface area values of Sorkheh variety showed significant differences from those of Sazandegi variety. The separation
of the grain mix in an air stream depends on not only the
ratio between the air velocity and the terminal velocity of
the particles but also on the quantity of particles entrained
per unit volume of the air flow. The rate of heat transfer to
the material also significantly depends on the heat transfer
surface. The smaller the volume of material per unit
surface, the better its condition for rapid heat transfer. The
effects of size and surface area on drying rates of
particulate materials can also be characterized by using
the surface to volume ratio. When diffusion of water within
the particle limits drying rate, larger particles dry more
slowly than smaller particles of the same shape. Also, the
ratio of surface area to volume affects drying time and
energy requirements