156 ILLINOIS ACADEMY OF SCIENCE 



NOTES ON THE PROPERTIES OF STEAM 



G. A. GOODENOUGH, UNIVERSITY OF ILLINOIS 



The various properties of saturated and superheated vapors, 

 pressure, temperature, volume, heat content, specific heat, etc., 

 are not independent, but connected by certain well-known ther- 

 modynamic relations. Consequently the values of these prop- 

 erties when collected in tabular form are consistent when 

 derived from formulas that satisfy the necessary thermo- 

 dynamic relations. 



The two most important relations are the following : 



fU=-"(S-), 



sat 

 The first is a statement that the rate of change of the spe- 

 cific heat of superheated vapor with the pressure, holding the 

 temperature constant, is with its sign changed equal to the 

 product of the temperature and the curvature of constant 

 pressure curves on the vT-plane. The second relation ap- 

 plies to the saturation condition and gives a relation between 

 latent heat r, change of volume v"-v' during vaporization, 

 and the slope $2- of the saturation curve. 



r dt 



In the case of water vapor, the series of experiments in 

 the Munich laboratory give fairly reliable information re- 

 garding the volume and specific heat of superheated steam. 

 The problem lies in the correlation of these experiments 

 through relation (1). It is one of exceeding difficulty, but 

 has been successfully solved in the University of Illinois in- 

 vestigations. The method of attack is as follows : 



A characteristic equation v=f (p,T) was chosen and the 

 constants were determined so as to satisfy the volume meas- 

 urements. From this equation the second member of ( 1 ) was 

 obtained and c p was then readily expressed as a function of T. 

 By adjustment of the constants, the resulting values of c p 

 were made to satisfy the specific heat measurements. Fin- 

 ally, the other properties derived from these equations were 

 made to satisfy the second relation and all other outstanding 

 requirements. 



The result of the work is a table of the properties of steam 

 that possesses absolute thermodynamic consistency and at the 

 same time extreme accuracy. 



