Carnot Cycle vs Rankine Cycle

Today I am going to tell you difference between Carnot cycle and Rankine cycle. Both Carnot cycle and Rankine cycle are air standard cycles. Carnot cycle is an ideal cycle of heat engine which gives highest efficiency between given temperature difference but it is a theoretical cycle and actually no engine works on Carnot cycle. Rankine cycle is an ideal cycle of vapor or steam power generation. All steam power plant work on this cycle. It used water as the working substance. Both these cycle have different features which I will describe below.

Carnot cycle has two isothermal processes and two isentropic processes. Heat is added and rejected isothermally and compression and expansion take place at constant entropy. It is a theoretical cycle but actually it is difficult to achieve isothermal heat addition and rejection. It gives highest efficiency between given temperature difference.

As I told Rankine cycle is a ideal vapor power generation cycle used in steam turbine. It consist two isobaric and two isentropic processes. Heat is added and rejected at constant pressure and expansion and compression of gas takes place isentropically. In practically, first water is pumped to a boiler where heat is added at constant pressure which converts water into steam. This high temperature steam rotates the turbine. This expansion of gas takes places isentropically. Now the heat is rejected into condenser at constant pressure which converts it into water. Now the water is pumped isentropically which complete the cycle. This cycle runs continuously which generate power.

The basic and main difference between Carnot and Rankine cycle is that in Carnot cycle heat is added and rejected at constant pressure and in Rankine cycle heat addition and rejection take place at constant pressure. The other main difference is that the Rankine cycle use water as working substance and Carnot cycle used air as working substance. There are many other differences which are describe below in tabular form.

 

Difference between Carnot Cycle and Rankine cycle:

Sr. No.	Carnot Cycle	Rankine Cycle
1.	It is a theoretical cycle. . It gives maximum efficiency between two temperature difference	This one is a practical cycle of steam engine and turbine.
2.	Heat is added and rejected at constant temperature.	Heat is added and rejected at constant pressure.
3.	It has highest efficiency between two temperature differences.	Rankine cycle has lower efficiency than Carnot cycle.
4.	Carnot cycle uses air as the working substance.	Rankine cycle uses water as working substance.
5.	Carnot cycle is ideal cycle for heat engine.	It is ideal cycle for vapor power engine.

Today we have discussed about main difference between Carnot cycle and Rankine Cycle. If you have any query regarding this article, ask by commenting.