Thermodynamics FIRST LAW OF THERMODYNAMICSThis example demonstrates thatFigure 19 T-s Diagram with Rankine Cyclespotential and kinetic energy terms areinsignificant for a turbine, since theDpe and Dke values are less than 1Btu/lbm.When the system (the fluid beingstudied) changes its properties(temperature, pressure, volume) fromone value to another as a consequenceof work or heat or internal energyexchange, then it is said that the fluidhas gone through a "process." Insome processes, the relationshipsbetween pressure, temperature, andvolume are specified as the fluid goesfrom one thermodynamic state toanother. The most common processesare those in which the temperature,pressure, or volume is held constantduring the process. These would beclassified as isothermal, isobaric, orisovolumetric processes, respectively.Iso means "constant or one." If thefluid passes through various processesand then eventually returns to thesame state it began with, the system issaid to have undergone a cyclicprocess. One such cyclic process usedis the Rankine cycle, two examples ofwhich are shown in Figure 19.The processes that comprise the cycleare described below.ab: Liquid is compressedwith no change inentropy (by ideal pump).bc: Constant pressure transfer of heat in the boiler. Heat is added to the compressedliquid, two-phase, and superheat states.cd: Constant entropy expansion with shaft work output (in ideal turbine).da: Constant pressure transfer of heat in the sink. Unavailable heat is rejected to theheat sink (condenser).Rev. 0 Page 61 HT-01
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