Four Processes in the Rankine Cycle

There are four important processes in the Rankine cycle. These states are identified by numbers as shown in Figure 5.6.

Figure 5.6 Rankine Cycle

Process 1–2 (Pumping Process): The working fluid is pumped from low pressure to high pressure, as the fluid is a liquid at this stage the pump requires some small amount of input energy.

Process 2–3 (Heating Process): The high pressure liquid enters a boiler where it is heated at constant pressure by an external heat source to become a dry saturated/superheated steam. The input energy required can be easily calculated using Mollier diagram or h–s chart or enthalpy–entropy chart also known as steam tables.

Process 3–4 (Expansion Process): The dry saturated or superheated steam expands in turbine. This decreases the temperature and pressure of the steam, and some condensation may occur. The output in this process can be easily calculated using the enthalpy–entropy chart or the steam tables.

Process 4–1 (Condensation Process): The wet vapour then enters a condenser where it is condensed at a constant temperature to become a saturated liquid.