BeginnerTopic 24 of 105Thermodynamics & Fluids
Carnot cycle
The ideal reversible engine with efficiency 1-Tc/Th.
In depth
Four reversible steps: isothermal heat addition, adiabatic expansion, isothermal heat rejection, adiabatic compression. Efficiency η=1-T_C/T_H depends only on the reservoir temperatures. It is the upper bound and the standard for comparing cycles.
Key points
- Not practical because of small work per cycle
- Absolute temperatures
- Applies to refrigerators in reverse
ExampleBetween 800 K and 300 K the maximum efficiency is 62.5%.
What is Carnot cycle?
The ideal reversible engine with efficiency 1-Tc/Th.
Why is it important to understand carnot cycle?
The Carnot cycle sets the maximum efficiency between two temperatures, so it is the benchmark used to judge real engines and plants.
Why is the Carnot efficiency the maximum?
It is reversible, and no real engine can be more efficient than a reversible engine working between the same two reservoirs.
Why is Carnot efficiency rarely reached in practice?
Real processes are irreversible and must transfer heat across finite temperature differences, so efficiencies fall well below the Carnot value.
How is Carnot cycle used in practice?
Typical applications include comparing the efficiency of a geothermal plant to the Carnot limit at its source temperature, setting a target for a new power cycle design and estimating the maximum possible efficiency of a solar thermal plant.
What should I learn before Carnot cycle?
Study "Refrigerators and heat pumps" first (topic 23 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
What are the key points of Carnot cycle?
Not practical because of small work per cycle. Absolute temperatures. Applies to refrigerators in reverse.
Can you give an example of Carnot cycle?
Between 800 K and 300 K the maximum efficiency is 62.5%.
What comes after Carnot cycle?
The next topic is "Entropy", which builds directly on this one.
How difficult is Carnot cycle?
It is classed as Beginner in Thermodynamics & Fluids (topic 24 of 105). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.