Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . 100 150 200 250 o300 350 400 Temperature C. Fig. 13. Values of the True Specific Heat of Superheated Steam. nations that have preceded, the construction of all the linesexcept EHS should be obvious. This line is obtained by calcu-lating the change or increase in the entropy of superheatedsteam for various values of temperature (between Ta and Ti) fromthe following well-known relations: THE ELEMENTARY THEORY OF HEAT 20 CpdTT or Cf>s - 4>l = Cpm I l0ge —S I =
Steam turbines; a practical and theoretical treatise for engineers and students, including a discussion of the gas turbine . 100 150 200 250 o300 350 400 Temperature C. Fig. 13. Values of the True Specific Heat of Superheated Steam. nations that have preceded, the construction of all the linesexcept EHS should be obvious. This line is obtained by calcu-lating the change or increase in the entropy of superheatedsteam for various values of temperature (between Ta and Ti) fromthe following well-known relations: THE ELEMENTARY THEORY OF HEAT 20 CpdTT or Cf>s - 4>l = Cpm I l0ge —S I = Cpm (logio T, - logio ^ J, where C^ is the mean value of the specific heat of steam takenfrom the curves in Fig. 12 for the temperature T8. The amount of energy that becomes available in the adiabaticexpansion of superheated steam is very easily expressed with. Fig. 14. Simple Temperature-Entropy Diagram for Superheated Steam. the help of Fig. 14a. Two conditions after expansion must beconsidered: (1) When the steam in the final condition is superheated, (2) When the steam in the final condition is wet (or drysaturated). Using Fig. 14a with the notation as before except that Eaa isthe available energy from the adiabatic expansion of steam ini-tially superheated in per pound, 08 and H8 are respec-tively the total entropy and the total heat of the superheated 30 THE STEAM TURBINE steam at the initial condition, then obviously from the diagram,when the steam is wet at the final condition, Hs — H3 + (03 — 0S) T3. (1) When the steam is superheated at the final condition, as, forexample, when the temperature after expansion is T2, Eas — Hs — H2 — (08 02) T2.* (1) It will be observed that these equations (1) and (i) are thesame in form as equation (1), page 23, and that equation (1)differs essentially in having the terms Hs and 08
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