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All standard heat engines (steam, gasoline, diesel) operate by applying heat to a gas, which expands in a cylinder and pushes a piston to perform its function. So it’s simple to see how to convert heat into work, but that’s a one-time deal. To have a useful engine, we need it to keep repeating. The simplest heat engine is known as the Carnot engine, and a Carnot cycle is one complete heating/cooling, expanding/contracting cycle back to the original gas volume and temperature.
What Is A Carnot Engine?
A Carnot engine is a heat engine that operates according to the Carnot cycle. The Carnot cycle estimates the maximum efficiency with which a heat engine can transform heat into output work when functioning between two reservoirs (hot and cold). Nicolas Leonard Sadi Carnot created the Carnot engine in 1824. Because of the name of its creator, this engine is recognised as a Carnot engine (Sadi Carnot).
The Carnot engine is a model engine that employs reversible mechanical and thermal interactions. This statement reflects the engine’s ability to complete its movement and return to its original state without growing entropy (without losing energy). The engine must be in thermal equilibrium throughout the cycle to return to its initial state without losing energy.
To better understand the meaning of the Carnot engine, we will explain a few terms:
Mechanical interactions: There is no heat transfer during the mechanical interaction process (Q = 0) because energy does not drop due to friction. This is known as an adiabatic process.
Thermal interaction: Heat transfer is extremely slow during the thermal interaction process (quasi-static). It means that the temperature difference between input/output and system heat is roughly the same, implying that heat transfer occurs over an infinitely long time. The intrinsic temperature of the system must remain constant during the thermal interaction. As a result, this process is known as the isothermal process.
Carnot Engine Principle
Nicolas Leonard Sadi Carnot designed the first Carnot engine in 1824. Benoît Paul Émile Clapeyron modified and expanded the existing model in 1834. And in 1857, Rudolf Clausius examined the engine for efficiency. This engine is said to work on a few principles, these principles are:
The efficiency of an irreversible heat engine is always less than that of a reversible one operating between the same two reservoirs.
All reversible heat engines operating between the same two reservoirs have the same efficiency.
It is critical to raise the temperature of the combustion room to improve the thermal efficiency of a gas power turbine. For example, turbine blades cannot withstand high-temperature gas, resulting in premature fatigue.
Carnot Cycle
To know the Carnot engine’s importance, we must know how the Carnot engine works. The Carnot engine works on the principle of the Carnot cycle.
Carnot cycle can be divided into four stages:
Isothermal Expansion: (A to B)
Line A to B in the diagram above symbolises the Isothermal Expansion process. The term isothermal is derived from the words “iso” and “thermal.”
Where “Iso” means “identical,” “temperature” implies “heat,” and “isothermal” indicates “no change in temperature.”
The gas expands during this isothermal expansion process, and this expansion works on the external environment by moving the piston upward. The pressure of the gas decreases during this process (as shown in the above diagram). However, the gas temperature does not change during this entire process, so it is referred to as an isothermal expansion (constant temperature expansion).
During this isothermal expansion, the gas absorbs heat energy QH from the high-temperature reservoir, increasing the entropy of the gas (energy).
Adiabatic Expansion: (B to C)
The gas expands indefinitely during the adiabatic expansion process. Its pressure decreases, Further, volume rises, and temperature decreases as some of the internal energy is lost in proportion to the work done.
This gas expansion process forces the piston upward and works on the external environment. The gas expansion cools the gas and transforms its temperature to a “cold” temperature without the addition of heat (Tc).
Isothermal compression (C to D)
The surrounding environment works on the gas during this process, causing heat to transfer from the system to the cold reservoir. The temperature of the gas remains constant during the isothermal compression process. Still, the pressure rises, and the gas volume falls. The heat energy is forced to move from the system to the cold reservoir due to this process, and the system’s entropy decreases.
Adiabatic Compression (D to A)
The line D to A in the above graph indicates the Adiabatic reversible compression process. The piston and cylinder are presumed to be isolated again during this process, and the hot reservoir is supposed to be removed. The environment continuously works on the gas during this stage by shifting the piston down.
As the piston descends further, it constantly compresses the gas and raises its temperature and pressure from P3 to P1 (as shown above). This process increases the internal energy of the gas, compresses it, and raises its temperature from Tc to Th. The entropy remains constant in the adiabatic process. The cycle then repeats itself.
What Is the Carnot Theorem?
If we follow Carnot Theorem, then it follows:
The productivity of all reversible heat engines operating between two similar reservoirs is the same.
The productivity of the reversible Carnot heat engine operating between the two reservoirs is higher than that of the irreversible heat engines operating on the same reservoirs.
A Carnot engine’s maximum efficiency is given below:
Conclusion
A Carnot engine is an engine that works on the principle of a Carnot engine. In this article, we have highlighted the meaning of the Carnot engine’s and the Carnot engine importance. The Carnot cycle is a complex process that is divided into four parts.
