22 
BULLETIN 509, U. S. DEPARTMENT* OF AGRICULTURE. 
been worked out, assuming the water to start with an initial tem- 
perature of 59° F. and to evaporate at the temperature t 3 , which is 
the temperature of the leaving air. The efficiency here expressed is 
the ratio of the total heat of water vapor at t 3 above 59° F. divided 
by the least possible expenditure of heat necessary to evaporate it 
under the assumed conditions of the entering and leaving air at 
atmospheric pressure. When the temperature t t of the entering air 
approaches that of the heated air t 2 — that is, when a high humidity 
is used — the calculations become very uncertain, since the quantity of 
air called for under the assumed conditions approaches infinity, 
while the temperature differences between t t and t 3 become infini- 
tesimal. 
The minimum volume of air required to evaporate 1 pound of 
water is also given in Table 2. 
Table 2. — Maximum possible theoretical heat efficiency of evaporation under 
given conditions (ti, t 2 , hi, h 3 ) at atmospheric pressure (760 mm.). 
Heat con- 
Total 
sumed to 
heat of 
Entering air. 
After heating. 
Leaving air. 
evaporate 
1 pound 
1 pound 
of vapor 
Minimum 
of water 
att 3 
volume 
Efficiency 
from 
above 
of air 
H-hG. 
initial 
initial 
required. 
tempera- 
ture of 
tempera- 
ture of 
ti 
h. 
u 
h 2 
ts 
h 3 
59° F. 
59° F. 
A 
B 
c 
D 
E 
F 
G 
H 
J 
K 
F. 
Perct. 
o p 
Perct. 
F. 
Perct. 
B.t.u. 
B. t. u. 
Cubic ft. 
32 
100 
95 
11 
65 
75 
2,353 
1,074 
2,163 
0.457 
59 
100 
95 
31 
76 
75 
2,100 
1,078 
3,426 
.514 
32 
100 
158 
2 
84 
75 
1,911 
1,080 
993 
.565 
59 
100 
158 
6 
92 
75 
1,715 
1,082 
1,126 
.631 
86 
100 
158 
13 
107 
75 
1,556 
1,087 
1,402 
.698 
32 
100 
212 
0+ 
97 
75 
1,758 
1,084 
694 
.617 
59 
100 
212 
2 
103 
75 
1,572 
1,086 
731 
.690 
86 
100 
212 
4 
114 
75 
1,422 
1,089 
796 
.767 
32 
100 
95 
11 
84 
25 
6,136 
1,080 
5,738 
.176 
32 
100 
158 
2 
110 
25 
2,972 
1,088 
1,495 
.366 
86 
100 
158 
13 
141 
25 
4,869 
1,098 
4,385 
.225 
32 
100 
212 
0+ 
126 
25 
2,352 
1,093 
930 
.457 
86 
100 
212 
4 
146 
25 
2,166 
1,099 
1,206 
.507 
32 
100 
95 
11 
60 
100 
1,974 
1,073 
1,836 
.544 
59 
100 
95 
31 
70 
100 
1,679 
1,076 
2,733 
.641 
86 
100 
95 
74 
88 
100 
1,476 
1,081 
9,725 
.733 
32 
100 
158 
2 
79 
100 
1,692 
1,079 
876 
.636 
86 
100 
158 
13 
99.5 
100 
1,390 
1,085 
1,329 
.781 
140 
100 
158 
63 
140.9 
100 
1,119 
1,098 
3,879 
.981 
32 
100 
212 
0+ 
90 
100 
1,582 
1,082 
625 
.684 
86 
100 
212 
4 
106 
100 
1,350 
1,087 
721 
.S04 
176 
100 
212 
47 
176.5 
100 
1,130 
1,108 
2,002 
.972 
IN WATER VAPOR ALONE. 
140 
100 
158 
63 
140 
100 
1,097 
1,097 
16,418 
1.00 
212 
100 
230 
71 
212 
100 
1,119 
1,119 
3, 657 
1.00 
212 
100 
320 
16 
212 
100 
1,121 
1,121 
664 
1.00 
