20 PROPERTIES OF STEAM AND OTH1.K VAPORS 



Rankine's Cycle. An important investigation for the steam-engine 

 may be made by aid of the accompanying figure* which represents the 

 indicator diagram from a rtMUB engine- without clear- 

 ance and with a nonconducting cylinder. Strain i> 

 admitted at an absolute pressure p l fiom a to b\ adia- 

 batic expansion follows from b to < ; finally tin steam 



K, .. i "is exhausted from c to d at the pressure- /).,. The 



external work during admission for one pound of steam having the 

 quality x t is 



Pi v i - Pi (*i*i + *); 

 the external work during expansion i> 



EI " E * = ~A (q * ~ q ** * lPl ~ X ^' f 

 and the external work during exhaust is 



Pf>* = P* (*2*> + *) 



which must be subtracted since it is done by the piston on the steam. 

 The effective work of the cycle is 



or substituting the proper values 

 W - (q, + x^ + Ap,x lUl -q, - xj> 2 - ApwJ -f 



the last term is small and may be dropped. 

 Remembering that 



r = p + Apu, 

 we have 



w = 



The values of r and q may be taken from Tables I, II, or III, and the 

 value of x 7 can be determined by aid of the equation 



By the first law of thermodynamics the difference between the heat 

 supplied to an engine and the heat rejected, is equivalent to the work 

 done, provided there are no losses; therefore, 



