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.
Related page:
1-5.Equilibrium moisture content and Critical moisture content – Influence of temperature and relative humidity 
1-6.The Local moisture content and the Average moisture content 
3-4.Five patterns of the drying curve 
1-3.How to expressions the moisture in the material 
1-8.Why is the constant drying period. – Moisture movement in wet material. 
4-5.Drying speed and angle of the hot air 
1-1.What is drying 
3-8.Three types of drying 3.Drying of the paint film and Membrane