Constant drying period is the mass of the water which evaporates per unit time and unit surface area.
The unit is kg/s㎡.

Constant drying rate Jc is expressed by the following equation.

kH: Mass transfer coefficient
Hw: Saturated absolute humidity in the wet-bulb temperature Tw
H : Absolute humidity of hot air
hc: Coefficient of heat transfer
T : Hot air temperature
Tw: Wet-bulb temperature
(Δhv)w: Evaporative latent heat at the wet-bulb temperature Tw

Material temperature of Constant drying period is equal to the wet-bulb temperature Tw when it is dried by convection heat transfer.
When Conduction heat transfer and Radiation heat transfer added, it will be higher than the wet-bulb temperature.

So Halogen heater, it is radiant heat transfer itself, the material becomes hot in proportion to the irradiation heat.
When it seems that a hot wind heater is breathed out above 327℃ (600K), or a solvent is evaporated, while the steam which occurred diffuses around, it is necessary to also take into consideration the quantity of heat heated by T from Tw.

This formula is made up of elements that does not depend on the material.
Therefore, Constant drying period is determined by the external element.

Next second chapter explains one of foreign elements, humidity.