PRINCIPLES OF NAVAL ENGINEERING 



Column 5 gives the enthalpy per pound of the 

 saturated liquid at the pressure and temperature 

 shown. The enthalpy of saturated water at 32 °F 

 and the corresponding saturation pressure of 

 0.08854 psis is taken as zero; hence, all enthalpy 

 figures indicate enthalpy with respect to this 

 arbitrarily assigned zero point. For example, 

 the enthalpy of 1 pound of saturated water at 190 

 psia and 377. 51°F is 350.79 Btu more than the 

 enthalpy of 1 pound of saturated water at 0.08854 

 psia and 32° F. 



Column 6 gives the enthalpy of evaporation, 

 per pound of working fluid— that is, the change in 

 enthalpy that occurs during evaporation. This 

 column is of particular significance since it in- 

 dicates the Btu per pound that must be supplied 

 to change the saturated liquid (water) to the 

 saturated vapor (steam) at the pressure and 

 temperature shown. In other words, the enthalpy 

 of evaporation is what we formerly described 

 as the latent heat of vaporization. 



Column 7 gives the enthalpy per pound of the 

 saturated vapor at the pressure and temperature 

 shown. Note that this is the sum of the enthalpy of 

 the saturated liquid and the enthalpy of evapora- 

 tion. 



Column 8 gives the entropy per pound of the 

 saturated liquid at the pressure and temperature 

 shown. The zero point for entropy, like the zero 

 point for enthalpy, is arbitrarily established at 

 32° F and the corresponding saturation pressure 

 of 0.08854 psia. 



Column 9 gives the entropy of evaporation 

 per pound of working fluid at the indicated pres- 

 sure and temperature. In other words, this 

 column shows the change of entropy that occurs 

 during evaporation. 



Column 10 gives the entropy per pound of the 

 saturated vapor at the pressure and temperature 

 shown. Note that this is the sum of the entropy of 

 the saturated liquid and the entropy of evapora- 

 tion. 



Columns 11 and J^ give the internal energy 

 of the saturated liquid and the internal energy 

 of the saturated vapor, respectively. 



In addition to giving properties of the satu- 

 rated liquid and the saturated vapor, theKeenan 

 and Keyes steam tables include data on the super- 

 heated vapor and other pertinent information. 



GRAPHICAL REPRESENTATION OF PROP- 

 ERTIES.— It is frequently useful to show the 

 relationship between two or more properties of 

 a working fluid by means of thermodynamic 

 graphs or diagrams. 



The relationships among pressure, volume, 

 and temperature of a perfect gas are sometimes 

 represented by a three-dimensional diagram of 

 the type shown in figure 8-12. The p-v-T sur- 

 face of a real substance may also be represented 

 in this way, but the diagrams become much more 

 complex because the relationships among the 

 properties are more complex. A simplified 

 p-v-T surface for water is shown in figure 8-13. 



147.65 

 Figure 8-12.— Three-dimensional representa- 

 tion of p-v-T surface for perfect gas. 



VOLUME 



147.66 

 Figure 8-13.— Three-dimensional representa- 

 tion of p-v-T surface for water. 



186 



