PROPERTY DIAGRAMS AND STEAM TABLES
Thermodynamics
Example 2: Use of steam tables
What are the specific volume, enthalpy, and entropy of steam having a quality of 90%
at 400 psia?
Solution:
From the steam tables at 400 psia:
nf = 0.01934
ng = 1.14162
hf = 424.2
hfg = 780.4
sf = 0.6217
sfg = 0.8630
n
= nf + x (nfg)
n
= 0.01934 + (0.9)(1.14162) = 1.0468 lbm/ft3
h
= hf + x(hfg)
h
= 424.2 + (0.90)(780.4) = 1126.56 Btu/lbm
s
= sf + x(sfg)
s
= 0.6217 + (0.9)(0.8630) = 1.3984 Btu/lbm-°R
If the substance is not water vapor, the "state" of the substance is usually obtained through the
use of T-s (temperature-entropy) and h-s (enthalpy-entropy) diagrams, available in most
thermodynamics texts for common substances. The use of such diagrams is demonstrated by the
following two examples.
Example 3: Use of the h-s diagram
Mercury is used in a nuclear facility. What is the enthalpy of the mercury if its pressure
is 100 psia and its quality is 70%?
Solution:
From the mercury diagram, Figure A-3 of Appendix A, locate the pressure of 100 psia.
Follow that line until reaching a quality of 70%. The intersection of the two lines gives
an enthalpy that is equal to h = 115 Btu/lbm.
HT-01
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