THE RANKINE CYCLE

The Rankine cycle is the most widely used cycle for electric power generation. Figure 2.1 illustrates a simplified flow diagram of a Rankine cycle. Figure 2.2 (a, b) shows the ideal Rankine cycle on P-v and T-s diagrams. Cycle 1-2-3-4- B-1 is a saturated Rankine cycle (saturated vapor enters the turbine). Cycle 1 ?-2 ?-3-4- B-1 ? is a superheated Rankine cycle.

Figure 2.1: Schematic flow diagram of a Rankine cycle.

Figure 2.2: Ideal Rankine cycles of the ( a) P-V and ( b) T-s diagrams. Line 1-2-3-4- B-1 = saturated cycle. Line 1 ?-2 ?-3-4- B-1 ? = superheated cycle. CP = critical point.

The cycles shown are internally reversible. The processes through the turbine and pump are adiabatic reversible. Hence, vertical on the T-s diagram. There are no pressure losses in the piping. Line 4- B-1-1 ? is a constant-pressure line.

The reversible Rankine cycle has the following processes:

Line 1-2 or 1 ? -2 ? . Adiabatic reversible expansion through the turbine. The exhaust vapor at point 2 or point 2 ? is usually in the two-phase region.

Line 2-3 or 2 ? -3. Constant-temperature and, being a two-phase mixture process, constant-pressure heat rejection in the condenser.

Line 3-4. Adiabatic reversible compression by the pump of saturated liquid at the condenser pressure, point 3, to subcooled liquid at the steam generator...