Tables 84—92 33 \ 



THERMODYNAMIC PROPERTIES OF MOIST AIR 



All material contained in Tables 84-92 has been specially prepared for this volume by 

 John A. Goff * and Serge Gratch. 2 The data are calculated on the basis of the Goff-Gratch 

 formulation of the thermodynamic properties of air and water vapor. The basic references 

 for this formulation are : 



1. "Final Report of the Working Subcommittee of the International Joint Committee 



on Psychrometric Data," by J. A. Goff. Paper presented before the American 

 Society of Mechanical Engineers, December 1948. Amer. Soc. Mech. Eng. Trans., 

 vol. 71, 1949. 



2. "Thermodynamic Properties of Moist Air," by J. A. Goff and S. Gratch, Trans. 



Amer. Soc. Heat, and Vent. Eng., vol. 51, pp. 125-128, 1945. Also: Heating, Piping 

 & Air Conditioning, ASHVE Journal Section, vol. 17, pp. 334-348, 1945. 



3. "Low Pressure Properties of Water from — 160 to 212 F," by J. A. Goff and S. 



Gratch. Trans. Amer. Soc. Heat, and Vent. Eng., vol. 52, pp. 95-129, 1946. 



At the Toronto (1947) meetings of the International Meteorological Organization, the 

 Aerological Commission, Subcommission on Physical Functions and Tables recommended " 

 the adoption of "the most acceptable values of aerological constants and functions con- 

 sistent with (a) present-day observational knowledge, (b) thermodynamic logic, and (c) 

 theoretical and practical requirements of aerology." It also recommended agreement with 

 those values adopted by the Working Subcommittee of the International Joint Com- 

 mittee on Psychrometric Data (see reference 1, above). With this in view, the Aerological 

 Commission recommended the adoption of the Goff-Gratch formulation of the thermo- 

 dynamic properties of air and water vapor. These recommendations were later approved 

 by the I. M. O. Twelfth Conference of Directors (Washington, 1947). 



The formulation provides for a consistent and logical system for the values of the 

 various thermodynamic parameters. In order to take into account the deviations of the 

 density of air and water vapor from ideal gas laws, the compressibility factors C and C, 

 were introduced into the respective equations of state (see Tables 84 and 91). The modi- 

 fications in the saturation vapor pressure over water and ice due to the presence of air 

 has been taken into account by the introduction of the factors fv> and fi respectively (see 

 Tables 89 and 90).* 



The unit of energy used throughout the discussion and tables to follow is the Inter- 

 national Steam Tables calorie, ITcal. (see Introduction, p. 4). Equations and footnotes 

 have been numbered consecutively in Tables 84-92 because of the frequent use of cross 

 references. 



All computations were carried out in the University of Pennsylvania Thermodynamic 

 Research Laboratory operated under contract with the Navy Department, Office of Naval 

 Research. 



Relative humidity. — For the purpose of thermodynamic analysis, moist air is to be 

 regarded as a mixture of only two constituents, namely, dry air and water vapor. The 

 mass of water vapor per unit mass of dry air is a convenient parameter in terms of which 

 to express the relative composition of the mixture. This parameter is called the mixing 

 ratio of the moist air and is denoted by the symbol r. At any pressure p and temperature 

 T within certain limits, 6 moist air can coexist in neutral or metastable equilibrium, over a 



1 Dean, Towne Scientific School, University of Pennsylvania; Director, University of Pennsylvania 

 Thermodynamic Research Laboratory. 



•Assistant Professor of Mechanical Engineering, Towne Scientific School, University of Pennsylvania; 

 Project Leader, University of Pennsylvania Thermodynamic Research Laboratory. 



* I. M. O. Aerological Commission, Doc. 25, Toronto, 1947. 



4 See also Sheppard, P. A., The physical properties of air with reference to meteorological practice 

 and air conditioning engineer. A paper presented before the American Society of Mechanical Engineers 

 in December 1948, Amer. Soc. Mech. Eng. Trans., vol. 71, 1949. 



6 At any given temperature T there is a lowest pressure p = ew(T) for saturation with respect to 

 liquid, where ew(T) denotes the saturation pressure of pure water vapor with respect to liquid water. 

 At and below this pressure, rw {p, T) ceases to exist and relative humidity, therefore, is not defined. 



At any given pressure p there is a highest temperature, namely, the solution of ev (T) = p, for 

 saturation with respect to liquid water. At and above this temperature, r»(/>, T) ceases to exist and 

 relative humidity, therefore, is not defined. 



{continued) 



SMITHSONIAN METEOROLOGICAL TABLES 



