# Carnot cycle vs. Rankine cycle: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on March 2, 2024
The Carnot cycle is an idealized thermodynamic cycle representing maximum efficiency, while the Rankine cycle is a practical cycle used in steam power plants.

## Key Differences

The Carnot cycle is a theoretical concept that represents the maximum possible efficiency a heat engine can achieve under certain conditions. In contrast, the Rankine cycle is a more practical model used for steam engines, particularly in power generation.
In the Carnot cycle, the working fluid undergoes a series of reversible processes: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression. The Rankine cycle, however, involves real processes: adiabatic expansion in a turbine, constant pressure heat rejection, adiabatic compression in a pump, and constant pressure heat addition in a boiler.
Efficiency in the Carnot cycle is determined by the temperature difference between the heat source and sink, and it is always higher than any real heat engine. The Rankine cycle's efficiency is lower due to irreversibilities and practical limitations like friction and heat losses.
The Carnot cycle is an ideal model used for theoretical purposes and sets an upper limit on the efficiency of heat engines. The Rankine cycle, on the other hand, is used to design and analyze actual power plants and steam engines.
The Carnot cycle assumes no entropy is generated, which is not achievable in reality. The Rankine cycle incorporates real-world factors such as the generation of entropy and non-ideal fluid properties, making it more applicable to real-world systems.

## Comparison Chart

### Nature

Theoretical, idealized
Practical, real-world

### Processes Involved

Real processes with irreversibilities

### Efficiency

Maximum possible
Lower due to practical limitations

### Application

Theoretical analysis
Design of steam power plants

### Entropy Generation

Zero (assumed)
Occurs due to irreversibilities

## Carnot cycle and Rankine cycle Definitions

#### Carnot cycle

A conceptual model for the most efficient heat engine cycle.
Engineers use the Carnot cycle as a benchmark for evaluating real-world engine efficiencies.

#### Rankine cycle

A real-world process involving steam generation, expansion, and condensation.
The Rankine cycle describes the operation of steam turbines and generators in a power station.

#### Carnot cycle

An ideal cycle with no entropy generation or losses.
While studying thermodynamics, students learn that the Carnot cycle represents an idealized, lossless process.

#### Rankine cycle

A common cycle for electricity generation using steam.
Engineers optimize the Rankine cycle to improve the efficiency of thermal power plants.

#### Carnot cycle

An idealized process involving reversible isothermal and adiabatic changes.
In textbooks, the Carnot cycle is depicted as a perfect model for heat engine cycles.

#### Rankine cycle

An applicable model for heat engines involving phase changes.
In the Rankine cycle, water undergoes phase changes to drive turbines and generate electricity.

#### Carnot cycle

A theoretical construct illustrating the upper limit of thermal efficiency.
The Carnot cycle sets an unattainable standard for efficiency in practical engines.

#### Rankine cycle

A thermodynamic cycle for steam engines with real-world inefficiencies.
Unlike the idealized Carnot cycle, the Rankine cycle accounts for real energy losses in steam engines.

#### Carnot cycle

A theoretical thermodynamic cycle demonstrating maximum efficiency.
The Carnot cycle is often used in thermodynamics to explain the efficiency limits of heat engines.

#### Rankine cycle

A practical thermodynamic cycle used in steam power plants.
Most thermal power plants operate based on the principles of the Rankine cycle.

## FAQs

#### What is the primary application of the Rankine cycle?

It's used to design and analyze steam power plants and turbines.

#### What is the Rankine cycle?

A practical thermodynamic cycle used in steam power plants.

#### Are there any practical implementations of the Carnot cycle?

No, it's a theoretical model and not used in practical applications.

#### What fluids are used in the Carnot cycle?

Any fluid can be used theoretically, as the cycle is idealized.

#### How does the Carnot cycle differ from real engines?

The Carnot cycle is theoretical and assumes no entropy generation or losses.

#### Why is the Carnot cycle important in thermodynamics?

It sets the theoretical upper limit for the efficiency of heat engines.

#### Is the Carnot cycle used in any educational contexts?

Yes, it's commonly used in thermodynamics education to explain concepts of efficiency.

#### What makes the Rankine cycle suitable for power plants?

Its practical design and ability to handle real-world thermodynamic processes.

#### Do the Carnot and Rankine cycles operate under the same principles?

They both follow thermodynamic laws, but the Carnot cycle is idealized while the Rankine cycle is practical.

#### What is the Carnot cycle?

An idealized thermodynamic cycle representing the maximum possible efficiency.

#### Can the Carnot cycle be used to improve real engine designs?

It serves as a benchmark, but direct application is not practical.

#### How does efficiency in the Rankine cycle compare to the Carnot cycle?

The Rankine cycle has lower efficiency due to practical limitations and irreversibilities.

#### What is the working fluid in most Rankine cycle applications?

Water, often in the form of steam.

#### How does the Rankine cycle handle phase changes?

It includes the boiling and condensation of water in its process.

#### Are there any variations of the Rankine cycle?

Yes, there are several modifications to improve efficiency and adapt to different conditions.

#### How does the environment impact the Rankine cycle?

Environmental conditions like temperature and pressure can affect its efficiency.

#### Can the Carnot cycle efficiency be achieved in practice?

No, due to real-world limitations like friction and heat losses.

#### What are the major components in a Rankine cycle?

Boiler, turbine, condenser, and pump.

#### How does the Carnot cycle aid in understanding heat engines?

It provides a fundamental understanding of the limits of efficiency and energy conversion.