The values given for total heat at various temperatures may be represented by : 



Where //=heat of liquid at existing pressure, 



r= latent heat of evaporation of saturated steam at this pressure, 

 C p mean specific heat at existing pressure and ultimate temperature, 

 T sup and T sat = temperatures of superheated and of saturated steam. 



The mean specific heat must be distinguished from the actual specific heat 

 at any temperature and pressure. The actual specific heat at a given pressure 

 and temperature is that corresponding to a change in temperature of one degree, 

 while the mean specific heat is the average for all temperatures from that of satu- 

 rated steam up to the ultimate temperature of the superheated steam at the 

 existing pressure. 



The temperatures given in the table are the ultimate temperatures of the super- 

 heated steam, the degree of superheat being represented by these ultimate 

 temperatures less that of saturated steam at a corresponding pressure. 



The specific volumes are based on values as given by Knoblauch, Linde and 

 Klebe. Of all the corrective characteristic equations for superheated steam, that 

 advanced by these authorities is probably the most satisfactory. This is : 



} 3 

 j-D 



Where /= pressures in kilograms per square meter, 

 v= volume in cubic meters, 

 T= absolute temperatures degrees centigrade, 

 a, B, C and D=constants. 



Reduced to English units, the pressures being in pounds per square inch, the 

 volume in cubic feet per pound and the temperature in degrees Fahrenheit this 



becomes : 



7150,300,000 

 ^=0.5962 T / (i-fo.ooi/j./) - = -0.0833 



In engineering work it is frequently necessary to know the mean specific 

 heat of superheated steam at a given pressure and temperature. Fig. i shows 

 graphically values of this mean specific heat for various temperatures and 

 pressures and has been computed from values of total heat as given in Marks 

 and Davis' steam tables. The calculation involved, expressed as a formula, is : 



H // 



Sp. Ht.=;=p ;p 



sup. sat. 



Where Sp. Ht.=mean specific heat at a given pressure and temperature, 



H=total heat of superheated steam at a given temperature and 



pressure, 



/&=total heat of saturated steam at the corresponding pressure, 

 T and T sat _= temperatures of superheated and saturated steam. 



