Handbook of Solvents - George Wypych - ChemTech - Ventech!

7.3 Drying of coated film 397
Figure 7.3.10. Schematic diagram of drying experiment apparatus.
ducts. To make the laminar airflow over the balance, the length of ducts and sizes are determined.
The experiment is usually conducted in a low air velocity so as the air not to disturb
the balance. Honeycomb style mesh is often helpful to filter the air and make the airflow a
laminar one. It enabled us to do the drying experiment at a higher velocity of air. The air velocity
can be as high as 1 ~ 2m/sec.
Actually the air velocity of industrial dryer is much higher than the experimental conditions
and the directions of flow are normally perpendicular to the coating surface, not parallel
with coating surface. Thus we can hardly expect to conduct a quantitative simulation
from this experiment, but we can find the characteristic drying curve and mechanisms of
drying of the given materials.
The drying rate of coating is the weight of solvent loss per time divided by the area of
evaporation.
where:
R
mass
R mass
dW W +Δ −W
=− ≈−
Adt AΔt t t t
evaporation rate
W weight of sample at a specific time
t time
Δt time interval between measurements
A evaporation area
[7.3.9]