30 BULLETIN 894, U. S. DEPARTMENT OF AGRICULTURE. 
Table 7. — Constant h. 
2.5 
7.0 
30 
80 
Latent heat of steam in B. t. u 
965 
956 
928 
890 
Temperature of steam (degrees F.) 
220 ' 232 
274 
324 
Kiln temperature. 
B. t. u. given off per square foot radia- 
tion per degree difference in tempera- 
ture=k. 
°F. 
120 
2.6 
2.2 
3.0 
2.6 
2.2 
130 
3.0 
2.6 
2.2 
1.0 
145 
3.0 
150 ! 
2.6 
180 
2.2 
1 

For instance, a kiln 39 feet long inside has 1,068 square feet radia- 
tion in the heating coils, 7 pounds steam pressure available, and 145 
degrees maximum entering air temperature. The difference in tem- 
perature between the steam in the coils and the entering air or flue 
temperature is 232 — 145 = 87 degrees Fahrenheit. Therefore the 
formula becomes — 
1068X87X2.2 
steam per hour. 
956 
CEILING COILS 
=216.1 pounds 
The ceiling coil steam consumption can be approximated with 
sufficient accuracy by the same method and the same constants. 
The amount of steam consumed during the early stages of a kiln 
run, when temperatures are lower and humidities higher, is about 
one-half as much per hour as under maximum temperature and 
minimum humidities. Allowance should be made for the radiation 
from all exposed steam mains and supplies. 
STEAM JET. 
The steam jet line consists of a pipe running the full length of the 
spray chamber and located near the sprays, as shown in the cross 
sections (figs. 1, 2, and 5). This pipe is perforated with f-inch holes 
at intervals of 12 inches, so as to discharge steam straight down the 
spray chamber. For kilns up to 30 feet long 1-inch pipe should be 
used, and for kilns over 30 feet long IJ-inch pipe. For kilns up to 
50 feet in length the spray pipe should be fed at one end and capped 
at the opposite end. For kilns over 50 feet long the steam should 
enter the Jet line at the middle of the kiln and both ends should be 
capped. 
The function of the steam sprays is to condition the lumber both 
prior to and during the drying operation. They may also be used 
