76 BULLETIN 1136, U. S. DEPARTMENT OF AGRICULTURE 
of lumber themselves equalize the various rates of fiow in the air as it 
reaches them. Two sets of steam spray lines may be provided, as 
shown, one set for use with outward circulation and the other for 
PX 
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 ——————— 
CoO nL re Xx] ROX RAT ALU SIL ee 
BORSA OARS PREI ESS PRE REPO APES ERA 
a eS 
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INLET DUCT | 
a Sal eae 
RETURN DUCT 
— x, ~- 
_ 
FETURN DUCT 
FALE SH All? INTAKE 
FIGURE 11.—Cross section of a typical] external-blower compartment kiln. The blower, 
drawing air over the heating coils, forces a current of air upward through the inlet 
duct and the chimney, through the kiln charge, as indicated by the arrows, downward 
into the return ducts, and then to the heating coils. Supplying some air from the 
intake reduces the humidity in the kiln, since the fresh air replaces moisture-laden air 
that ordinarily escapes through leakage; exhaust flues, however, are necessary with 
rapid drying rates Z 
inward. Since the circulation-producing effect of the steam jets is not 
needed, however, a simpler arrangement with a single steam line 
running along the bottom of the kiln near the center and a single jet 
located at each fan has been developed. 
