Understanding the Rankine Cycle Processes

The Rankine cycle is an idealized thermodynamic cycle that describes the process by which certain heat engines, such as steam turbines or reciprocating steam engines, convert heat into mechanical work. It is the fundamental operating cycle of thermal power plants that use water as the working fluid.

The Rankine cycle consists of four main processes:

1. Process 1-2: Isentropic Compression
   This process involves the working fluid (water) being pumped from low pressure to high pressure. The pump does work on the fluid. This process is considered isentropic, meaning it is adiabatic (no heat transfer) and reversible.
2. Process 2-3: Isobaric Heat Addition
   The high-pressure liquid enters a boiler where it is heated at constant pressure (isobaric). The fluid absorbs heat from an external source, converting it into high-pressure, high-temperature steam.
3. Process 3-4: Isentropic Expansion
   The high-pressure steam expands through a turbine, producing work. This expansion is also considered isentropic (adiabatic and reversible). The temperature and pressure of the steam decrease during this process.
4. Process 4-1: Isobaric Heat Rejection
   The low-pressure steam from the turbine enters a condenser, where it is condensed back into a saturated liquid at constant pressure (isobaric). Heat is rejected from the fluid to a cooling medium.

Looking at these four processes, we can identify that the Rankine cycle is composed of:

• Two isobaric processes (constant pressure): Heat addition in the boiler (2-3) and heat rejection in the condenser (4-1).
• Two isentropic processes (constant entropy, adiabatic and reversible): Compression in the pump (1-2) and expansion in the turbine (3-4).

Therefore, the Rankine cycle consists of two isobaric and two isentropic processes.