Rankine Cycle

In a Rankine cycle (select "Rankine cycle" from drop down menu to view schematic of cycle), high-pressure liquid water (1) enters a boiler where it is heated to saturation temperature (2), vaporized, and superheated (3). The superheated steam is fed to a steam turbine, where it expands and generates mechanical work. The steam exits the turbine at a lower pressure and temperature as either superheated steam or steam at saturation temperature with a quality (4). This steam condenses (5), and a pump compresses the liquid water to high pressure (1). The cycle is shown on a pressure-enthalpy () diagram. Use sliders to vary the inlet pressure to the turbine and to select one of four outlet pressures . Use a slider to vary the turbine efficiency , which is the ratio of work produced by the turbine to the work produced by a reversible turbine between the same inlet and outlet pressures. The pathway for the irreversible turbine () is the thick dashed line on the diagram; the reversible turbine pathway is represented by the thin dotted line. Select "turbine" from the drop-down menu to show the inlet and outlet conditions for the turbine and the work generated.
  • Contributed by: Rachael L. Baumann
  • Additional contributions by: John L. Falconer and Nick Bongiardina
  • (University of Colorado Boulder, Department of Chemical and Biological Engineering)


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The inlet temperature to the turbine, (°C) is set; you can vary the inlet and outlet pressures (MPa). From these conditions the enthalpy (kJ/kg) and entropy (kJ/[kg K]) are obtained from the superheated steam tables.
The superscript denotes reversibility. A reversible steam turbine is isentropic, so , where is the entropy of the steam exiting a reversible turbine.
If at , then the reversible outlet state is superheated.
If at , then the outlet steam is at saturation temperature and consists of liquid and vapor. The quality of the steam is:
where is the fraction of vapor, and the superscripts and refer to saturated liquid and saturated vapor.
Depending on the quality of the exiting steam, is obtained from either the saturated steam tables or the superheated steam tables.
If , and is found in the superheated steam tables at and .
If , and .
The change in enthalpy for the reversible turbine is the work for the reversible process.
The efficiency indicates the turbine irreversibility and is the ratio of irreversible work to reversible work. For the irreversible turbine:
The screencast video at [1] shows how to use this Demonstration, and the video at [2] explains the cycle.
[2] Power Cycle Introduction [Video]. (Mar 15, 2012) www.youtube.com/watch?v=BA77fu3zAbs.
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