Rankine Cycle Theory

Rankine Cycle Theory

Rankine cycle is a heat engine with vapor power cycle. The common working fluid is water. The cycle consists of four processes:
1 to 2: Isentropic expansion (Steam turbine)
2 to 3: Isobaric heat rejection (Condenser)
3 to 4: Isentropic compression (Pump)
4 to 1: Isobaric heat supply (Boiler)



Work output of the cycle (Steam turbine), W1 and work input to the cycle (Pump), W2 are:

W1 = m (h1-h2)
W2 = m (h4-h3)

where m is the mass flow of the cycle. Heat supplied to the cycle (boiler), Q1 and heat rejected from the cycle (condenser), Q2 are:

Q1 = m (h1-h4)
Q2 = m (h2-h3)

The net work output of the cycle is:

W = W1 - W2

The thermal efficiency of a Rankine cycle is:

The efficiency of the Rankine cycle is not as high as Carnot cycle but the cycle has less practical difficulties and more economic.
The Isentropic efficiency of a turbine is a comparison of the actual power output with the Isentropic case. Typical Isentropic efficiencies range from 70-90%.



To calculate these enthalpy changes, you need to know the initial and final states, for example, temperature and pressure, of the working fluid for both the actual and isentropic cases. In the isentropic case, h2s is found from P2