. Applied thermodynamics for engineers. Q Fig. 160. Arts. 365, 3(>6, 379. -of Steam Formation. Paths 366. Path during Evaporation. Starting at 32°, the path of thesubstance during heating and evaporation at constant pressure wouldbe any of a series of lines aef\ ahi^ etc. The curve ab is sometimescalled the locus of boiling points. If superheating at constant pres-sure occur after evaporation, then (assuming Charles law to hold)the paths will continue as fg^ ij\ straight lines converging at a saturated vapor, wet or dry, the isothermal can only be a straightline of constant pressure.
. Applied thermodynamics for engineers. Q Fig. 160. Arts. 365, 3(>6, 379. -of Steam Formation. Paths 366. Path during Evaporation. Starting at 32°, the path of thesubstance during heating and evaporation at constant pressure wouldbe any of a series of lines aef\ ahi^ etc. The curve ab is sometimescalled the locus of boiling points. If superheating at constant pres-sure occur after evaporation, then (assuming Charles law to hold)the paths will continue as fg^ ij\ straight lines converging at a saturated vapor, wet or dry, the isothermal can only be a straightline of constant pressure. 367. Entropy Diagram. Figure 161 reproduces Fig. 160 on theentropy plane. The line ab represents the heating of the water atconstant pressure. Since the specific heat is slightly variable, the 238 APPLIED THERMODYNAMICS increase of entropy must be computed for small differences of tem-perature. The more complete steam tables give the entropy at variousboiling points, measured above 32^. Let evaporation occur when the. 0 g M c p Fig. 161. Arts. 367, 309-373, 376, 379, 386, Steam Dome. temperature ^s Tf,. The increase of entropy from the point b (sincethe temperature is constant during the formation of steam at constantpressure) is simply L^^Tf, + ), which is laid off as be. Otlierpoints being similarly obtained, the saturation curve cd is paths from liquid at 32° to dry saturated steam are abc, a VN^aJJS, etc. The factor of evaporation may be readily illustrated. Let the areae ?7>6»f represent L^^o, the heat necessary to evaporate one pound from andat 212° F. The area gjhch represents the heat necessary to evaporate onepound at a pressure h from a feed-water temperature j. The factor ofevaporation is gjhch-7- eUSf For wet steam at the pressure h, it is, forexample, gjhik -^ eUSf 368. Specific Volumes: Analytical Method. This was developed byClapeyron in 1834. In Fig. 162, let abed represent a Carnot cycle inwhich steam is the working substance and
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