22 



BULLETIN 509, U. S. DEPAETMENT* OF AGRICULTURE. 



been ^Yorked out, assuming the water to start with an initial tem- 

 perature of 59° F. and to evaporate at the temperature tj, w^iich is 

 the temperature of the leaving air. The efficiency here expressed is 

 the ratio of the total heat of water vapor at tg above 59° F. divided 

 by the least possible expenditure of heat necessary to evaporate it 

 under the assumed ccfnditions of the entering and leaving air at 

 atmospheric pres^re. When the temperature t^ of the entering air 

 approaches that of the heated air tg — 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 bet.ween t^ and t^ 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, tn, hi, hs) at atmospheric pressure {760 mm.). 















Heat con- 

 sumed to 



Total 

 heat of 







Entering air. 



After heating. 



Leaving air. 



evaporate 

 1 pound 

 of water 

 from 

 initial 

 tempera- 

 ture of 

 59° F. 



1 pound 

 of vapor 

 atts 

 above 

 initial 

 tempera- 

 ture of 

 59° F. 



Minimum 

 volume 



of air 

 required. 



Efficiency 

 H-^G. 



ti 



hi 



t2 



h2 



t3 



h3 



A 



B 



c 



D 



E 



F 



G 



H 



J 



K 



" F. 

 32 

 59 



Perct. 

 100 

 100 



jr. 



95 

 95 



Perct. 

 11 

 31 



° F. 



65 



76 



Perct. 



75 

 75 



B.t.u. 

 2,353 

 2,100 



B. t. u. 

 1,074 

 1,078 



Cubic ft. 

 2,163 

 3,426 



0.457 

 .514 



32 

 59 

 86 



100 

 100 

 100 



158 

 158 

 158 



2 

 6 

 13 



84 

 92 

 107 



75 

 75 

 75 



1,911 

 1,715 

 1,556 



1,080 

 1,082 

 1,087 



993 

 1,126 

 1,402 



.565 

 .631 

 .698 



32 

 59 

 86 



100 

 100 

 100 



212 

 212 

 212 



0+ 



2 



4 



97 

 103 

 114 



75 

 75 

 75 



1,758 

 1,572 

 1,422 



1,084 

 1,086 

 1,089 



694 

 731 

 796 



.617 

 .690 

 .767 



32 



100 



95 



11 



84 



25 



6,136 



1,080 



5,738 



.176 



32 



86 



100 

 100 



158 

 158 



2 

 13 



110 

 141 



25 

 25 



2,972 

 4,869 



1,088 

 1,098 



1,495 

 4,385 



.366 

 .225 



32 



86 



100 

 100 



212 

 212 



0+ 

 4 



126 

 146 



25 

 25 



2,352 

 2,166 



1,093 

 1,099 



930 

 1,206 



.457 

 .507 



32 

 59 



86 



100 

 100 

 100 



95 

 95 

 95 



11 

 31 



74 



60 

 70 



88 



100 

 100 

 100 



1,974 

 1,679 

 1,476 



1,073 

 1,076 

 1,081 



1,836 

 2,733 

 9,72.5 



.544 

 .641 

 .733 



32 

 86 

 140 



100 

 100 

 100 



158 

 158 

 158 



2 

 13 

 63 



79 

 99.5 

 140.9 



100 

 100 

 100 



1,692 

 1,390 

 1,119 



l,079i 

 1,085 

 1,098 



876 

 1,329 

 3,879 



.636 



.781 

 .981 



32 

 86 

 176 



100 

 100 

 100 



212 

 212 

 212 



0+ 

 4 

 47 



90 

 106 

 176.5 



100 

 100 

 100 



1, 582 

 1,.350 

 1,130 



1,082 

 1,087 

 1,108 



625 



721 



2,002 



.684 

 .804 

 .972 



IN WATER VAPOR AI.ONE. 



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 



