230 



KANSAS UNIVERSITY SCIENCE BULLETIN. 



vaporization takes place, the entroiay of vaporization will be -^, and 

 the total entropy of the liquid and vapor will be 



xr . 7 T 



^+ CylogeYT, 



To show the connection between the entropy diagram and the 

 steam-engine-indicator diagram, it is best to consider the thermody- 

 namic action of the whole system — boiler, engine, condenser, and feed- 

 water heater. Although the consecutive operations for turning heat 

 into work take place in different organs of the system, these consecu- 

 tive operations may be considered as the successive phases of a closed 

 cycle in which we have (see fig. 1), first, the line ah, representing 

 evaporation of the liquid in the boiler, at temperature T, into steam 

 of quality of dryness x. Work is done during this process at con- 

 stant pressure on the piston. The volume of the pound of water will 



Fig. 1. 



not vary very much from .017 cubic feet ; h represents the volume of 

 the pound of liquid after it has been expanded into steam. Assuming 

 that evaporation has taken place, suppose the steam to be allowed to 

 expand in such a manner that at all pressures it remains dry ; that is, 

 none of it condenses, and it is not superheated. We may plot these 

 volumes at various pressures by inserting the known specific volumes 

 of steam. The line he is thus plotted. The next process in the sys- 

 tem as a whole is the behavior, after expansion, of this one pound of 

 steam at temperature 212° F. and atmospheric pressure. This step is 

 condensation into feed water. This condensation occurs at constant 

 pressure of the atmosphere, and will consequently be represented by 

 the constant pressure line cd, indicating a diminution in volume from 

 about 26 cubic feet to about .017 cubic feet. The last stage is repre- 



