The drying speed is taken along a vertical axis, average moisture content is taken along a horizontal axis and the above figure is described, it will become a dry characteristic curve.

The drying speed is quantity of water evaporating in a unit time.

The drying speed has two definitions, the dry area standard Ja and the material mass standard Jm.

A: Drying area
Ms: Material mass
dmw: Water content change
dt: Time change
dw: Initial moisture content

Area based drying speed Ja = -1/A x dmw /dt = -Ms/A x dw/dt

Mass based drying speed Jm = -1/Ms x dmw /dt = -dw/dt

Relationship of area based drying speed Ja and mass based drying speed Jm

Area based drying speed Ja = Ms/A x Jm

Mass based drying speed Jm = A/Ms x Ja

*The dry characteristic curve varies according to type, kind and shape of materials.