30 PROPERTIES OK STEAM AND Oil IKK VAPORS. 



final results of computations and their limits known, arc not likely to 

 cause trouble. 



On the other hand tin- error of half a hundredth of a unit of entropy 

 will at 400 correspond to 0.51 of a per cent of priming or moisture in 

 the steam, and will carry a like error into all of the work. This uncer- 

 tainty of using the table without interpolation will he nearly the .same 

 throughout the table. 



Should the errors named be considered to be too large in any 

 greater accuracy can be had by interpolation. Direct interpolation for 

 temperature or for entropy can be made with facility; cross-interpolation 

 will be somewhat more troublesome. 



The use of the tables can best be illustrated by a few examples. 



Example i. Given the pressure by the gauge 150.3 pounds (165 

 absolute) and the priming 2.0 per cent i.v = 0.980) to find the entropy, 

 heat contents and specific volume. This condition is found most nearly 

 on page 78 and gives 



$ i . 54 xr -f q = 1176.8 v = 2. 699. 



Example 2. Given the pressure 150.3 pounds by the gauge and the 

 temperature 508 F., to find the entropy, heat contents and sp 

 volume. The superheating is 142 and the temperature of saturated 

 steam corresponding to 165 pounds absolute is 366 F. These conditions 

 are found on page 93 and give 



<f> = 1.65 r + q + c p (/-/,) = 1274 v = 3.395. 



Example 3. Required the amount of heat changed into work 

 pound of steam for Rankine's cycle, the initial pressure being 150.3 

 pounds by the gauge and the exhaust being under a vacuum of 26 inches 

 of mercury. The steam initially has i.o per cent of priming, and the 

 barometer stands at 30 inches of mercury. 



The exhaust pressure is 4 inches of mercury which by Table* XIV 

 corresponds to 1.96 pound. The initial absolute pressure is found by 

 adding the equivalent of 30 inches of mercury or 



14.7 pounds to 150.3 giving 165.0. 

 The solution of this problem is found in the column for entropy 



