334 TABLE 8S 



ENTHALPY RESIDUAL OF MOIST AIR 



(Further explanation on p. 331.) 

 The enthalpy residual Ah of moist air is defined by 



h=. 7 -R\t + *. (r/c) (* + 1354.74) ] + Ah, (9) 



where h is the enthalpy of moist air per unit mass of dry air according to the Goff-Gratch 

 formulation. The constant 1354.74 °C. is the numerical value of the quantity, eL„(0)/4i?, 

 where L v (0) is the latent heat of vaporization of water at C C. (Table 92). 



In Table 85 are listed values of enthalpy residual Ah as a function of pressure p, tem- 

 perature t, and relative humidity U. The unit of energy is the International Steam Tables 

 calorie (ITcal.) defined in terms of the absolute watthour (whr) by the conversion factor, 

 860/1.00019 ITcal. whr 1 , which is equivalent to 



1 ITcal. = 4.18684 X 10 T erg (10) 



making 



i? = 0.068557 ITcal. "K." 1 (gram dry air)' 1 (11) 



The enthalpy of moist air is a relative quantity subject to augmentation by amount 

 A + rB, where A and B are constants that can be disposed of quite arbitrarily. For the 

 present purpose, the residual Ah has arbitrarily been assigned the value zero at r = 0, 

 t = °C., p = 0; the quantity Ah/r has arbitrarily been assigned the value zero at 

 r = CO, f = °C, p = e w (0) =6.1078 millibars in conformity with the usual steam 

 tables practice. 



Linear interpolation is valid throughout Table 85. Below °C. the dependence of 

 enthalpy residual on relative humidity is entirely negligible. To aid interpolation, zero- 

 pressure values for dry air (r = 0) are listed in the column U = even though relative 

 humidity is not defined at this pressure (see footnote 5, p. 331). In the region covered by 

 Table 85, the enthalpy residual lies between — 0.20 and +0.05 ITcal. (gram dry air)" 1 , 

 which means that it can safely be disregarded in rough calculations. 



(continued) 



SMITHSONIAN METEOROLOGICAL TABLES 



