FOREST SERVICE WATER SPRAY DRY KILN. 
21 
5. In the case of a single kiln or the end compartment of a bat- 
tery of kilns haYing side spray chambers, the heat loss through the 
outside wall need not be considered, as it actually assists the water 
sprays in lowering to the dew point the air leaving the lumber. 
Except in extreme cases, the heat passing off from the lumber in the 
form of vapor is sufficient to take care of radiation losses through the 
ceiling and walls of the kiln. 
The following formula and constants have been established from 
the experience obtained in connection with design of commercial 
kilns and from results of tests made in laboratory kilns. Theoreti- 
cally it is not correct to consider that the heat required is propor- 
tional to the size of the kiln, since it varies directly with the quantity 
of air in circulation passing over the heating coils; the greater the 
circulation the greater the heat radiated per square foot of heating 
surface. However, since so many local variable factors influence 
this quantity in different kilns, and since the circulation in the water- 
spray kilns may be assumed as approximately equal in different 
cases, it has been found that an empirical rule such as here given is 
sufficiently accurate for estimating purposes. 
WXHXK=R 1 
W= Width of the kiln above rail, in feet. 
H=Average height of kiln above rail, in feet. 
K= Constant from table below. 
R x = Radiation surface required per linear foot of kiln. 
Table 3 .—Constant "K." 
Maxi- 
mum 
tempera- 
ture and 
25 per 
cent hu- 
midity. 
rounds steam pressure. 
2.5 
7 
30 
80 
120 
130 
145 
160 
180 
Constant. 
0.10 
.166 
Constant. 
0.075 
.130 
.166 
Constant. 
Constant. 
0.090 
.125 
.166 
0.055 
.085 
.120 
.166 
The above formula gives the radiation per linear foot of kiln. 
To find the number of pipes required : 
5-* 
A=area of 1 foot of pipe (see Table 4). 
P=number of pipes required in cross section of kiln. 
