PROPERTY DIAGRAMS AND STEAM TABLES ThermodynamicsExample 2: Use of steam tablesWhat 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 = 0.01934ng = 1.14162 hf = 424.2hfg= 780.4 sf = 0.6217 sfg = 0.8630n= nf + x (nfg)n= 0.01934 + (0.9)(1.14162) = 1.0468 lbm/ft3h = hf+ x(hfg)h = 424.2 + (0.90)(780.4) = 1126.56 Btu/lbms = sf + x(sfg)s = 0.6217 + (0.9)(0.8630) = 1.3984 Btu/lbm-°RIf the substance is not water vapor, the "state" of the substance is usually obtained through theuse of T-s (temperature-entropy) and h-s (enthalpy-entropy) diagrams, available in mostthermodynamics texts for common substances. The use of such diagrams is demonstrated by thefollowing two examples.Example 3: Use of the h-s diagramMercury is used in a nuclear facility. What is the enthalpy of the mercury if its pressureis 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 givesan enthalpy that is equal to h = 115 Btu/lbm.HT-01 Page 50 Rev. 0
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