1 1 IK TABLES AND DIAGRAMS 25 



lems that involve hygrometric conditions. Aft b customary in present 



tabular values are based on th. wri^ht i han the volume 



of the dry air. The three column-* of thermal magnitudes may require 



The first of these gives the heat content 

 pound of dry air above o F. The values were obtained from Swann's 

 expression for the specific heat of air, nam 



r,- 0.24112 + 0.000009 /. 

 I IK next column gives the heat required to vaporize the weight of 



: n.jtiii.,1 t<> saturate tin- air at the given trtnjH-r.ittir.-. BckiW 

 ;>-> degrees thr hrat of MiMiiiMtion rather than the latent heat of vapor- 

 ization is used. I 'hr third . .: thr three columns gives the heat cot 

 of thr mixturr. ami thr values are obtained by adding the corresponding 

 values fa the other columns, Stri.tly ^M-akin^. the term "heat content" 

 U improper in this >nn< -. ti-.n, because- thr heat of the liquid is not in- 

 cludrd. Thr hrat ouitrnt ..i a non-saturated mixture with known rela- 

 ti\r humidity ma\ U- found with Millicient accuracy from the first two 

 of these three columns. Multiply the talmlar value in the second col- 

 umn by thr relative humidity and add the product to the value in the 

 fir-t column. Thu- with a trmjx-raturc of 80 F. and relative humidity 

 of 0.70, tlu hrat < .nteni of i pound of air with the contained water 

 vapor i- 



0.70 X 23.31 - 35.64 B.t.u. 



Tables 7, 8, 9, and 10 for ammonia ronvs|>ond to Tables I, 2, 3. and 5 

 for wat< r \ a|x>r, and require no special comm< 



The Diagrams. For the expedition-* solution of many engineering 



problems in whirh extreme accuracy i- not required the tables of prop- 



- may be replaced by certain graphical (harts. It U perhaps true 



that tlu valur <>t Mich graph ii al aids is generally overestimated, and that 



most proMrm- (an IK \\orkrd from the tables with the expenditure of 



\ little m<>iv time and rtt.rt and with much greater accura* 



While any two of the variables p. r. / may be taken as the 



ordir. i abscissa, resp . the M oilier chart, in which i and i 



are so used, has important advantages. 



Two M oilier diagrams, <>; -team and one for ammonia, accom- 



pany these tables. These differ in one essential respect. In the case of 

 m the properties of the medium near the liquid state are rarely 

 needed, hem r thr (hart inrlnd<- <nly the properties near the saturation 

 limit and in the region of superheat. In the case of ammonia, on the 

 other hand, the liquid curve must be included on account of the phe- 

 nomena connected with the free expansion of the fluid through the expan- 

 sion valve. Therefore the ammonia diagram has two parts, one showing 

 the properties in the region of superheat and near the saturation curve, 

 the other the properties near the liquid curve. 



