KILN DRYING HANDBOOK rire 
While it is obvious that many arrangements of fans and of heat- 
ing systems are possible, American manufacturers employ only the 
one illustrated, namely, a single central fan shaft and heating coils 
on each side, all located below the lumber. A German type recently 
introduced in the United States has a similar arrangement of fan 
shaft and of coils, but all this equipment is placed above the lumber. 
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DISC FANS 
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Figur® 12.—Cross section of a typical internal-fan kiln. The chief part of the circula- 
tion is crosswise, in the direction of the arrows. A series of disk fans, mounted with 
a spacing of 6 to 8 feet on a shaft that extends the full-length of the kiln, draws air 
over the heating coils and forces it upward through distributors that also exend the 
length of the kiln. The direction of air circulation may be reversed by reversing the 
direction of retation of the fans. in several commercial designs the distributors 
are dispensed with, the lumber itself and the heating pipes being relied upon to 
distribute the air 
SUPERHEATED-STEAM COMPARTMENT KILNS 
_The superheated-team kiln is comparatively simple. The essen- 
tials of its construction and operation are merely these: Provision 
must be made for high-pressure steam for the heating coils and the 
