. Applied thermodynamics for engineers. present total heats of wet vapor above 32 expansion proceeds from the superheated to the saturated region^ V ^9 ^9 ^:^ = p\(uJ^s) + (w-7i)\-P{^XU-\-s) + h + r +^Oi^_jr_XB, in which 7i = u-\- s is the volume of saturated steam at the pressure p,w is the volume of superheated steam, and p(w — n) is the internal energy measured above saturation.* This also re-duces to q— Q + s(^p — P), where q is the total heat in the super-heated steam, and the same form ofexpression will be found to apply toexpansion wholly in the superheatedregion. The gain in
. Applied thermodynamics for engineers. present total heats of wet vapor above 32 expansion proceeds from the superheated to the saturated region^ V ^9 ^9 ^:^ = p\(uJ^s) + (w-7i)\-P{^XU-\-s) + h + r +^Oi^_jr_XB, in which 7i = u-\- s is the volume of saturated steam at the pressure p,w is the volume of superheated steam, and p(w — n) is the internal energy measured above saturation.* This also re-duces to q— Q + s(^p — P), where q is the total heat in the super-heated steam, and the same form ofexpression will be found to apply toexpansion wholly in the superheatedregion. The gain in kinetic energyof a jet due to adiabatic expansion toa lower pressure is thus equivalent tothe decrease in the total heat of thesteam plus the work which would berequired to force the liquid backagainst the same pressure head. InP^ig. 237, let ab^ AB, 01)^ represent the three paths. Then thelosses of heat are represented by the areas dabc, deABc^ deCDfc. * For any gas treated as perfect, the gain ©f internal energy from tio T is. Fig. 237. Art. 515. — Adiabatic HeatDroiD. y E (T-t) PV—pv or in this case, since internal energy is gained at constant pressure, _ p(tv — n) y-i 366 APPLIED THERMODYNAMICS The term s(j)—P) being ordinarily negligible, these areas also rep-resent the kinetic energy acquired, which may be written In the turbine nozzle, the initial velocity may also, without seriouserror, be regarded as negligible; whence y2 — =q-Qov 7 = (g -Q)=223MVq~Q feet per second. 516. Computation of Heat Drop. The^valueoi q— Q may be determinedfor an adiabatic path between stated limits from the entropy diagram,Fig. 175, or from the Mollier diagram, Fig. 177. Thus, from the lastnamed, steam at 100 lb. absolute pressure and at 500° F. contains 1273B. t. u. per pound; steam 85 per cent dry at 3 lb. absolute pressurecontains 973 B. t. u. Steam at 150 lb. absolute pressure and 600° F. con-tains 1317 B. t. u. If it expand adiabatically to lb. absolute p
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