Thermodynamics – Carnot Cycle

The Carnot cycle consists of two isothermal and two adiabatic cycles, the most effective heat engine cycle. Physical physics allows the Carnot cycle to be the most effective heat engine cycle possible. When the second rule of thermodynamics dictates that not all of the heat given to a heat engine may be utilised to produce work, the Carnot considers the proportion of the heat that can be used in this way. The activities involved in the heat engine cycle have to be reversible and require no change in entropy to reach Carnot efficiency. The Carnot cycle is ideal because no real engine operations are reversible and all-natural physical processes entail some rise in entropy.

Carnot cycle

The Carnot cycle is an idealised thermodynamic cycle that happens in a machine or computer when it absorbs an amount of heat Q1 from a higher-temperature source and emits heat Q2 to a lower-temperature source, resulting in work on the outside. According to Carnot, a heated body that creates heat is required and a cool body whereby the caloric is delivered, resulting in mechanical labour. It also proves that the work is independent of the material utilised to generate heat and the machine’s design and construction material.

Coming up next are four reversible cycles that make up the Carnot cycle:

(Process 1-2): Reversible isothermal expansion: With just a tiny difference in temperature between the source of heat and the cylinder, heat transfer happens. As a result, it’s a reversible heat transmission method. The gas in their in-cylinder increases gently, exerting effort on its surroundings while keeping a steady temperature TH. The total quantity of heat transmitted to the gas is QH during this process.

(Process 2-3): Reversible adiabatic expansion: Whenever the heat stimulus is removed, the gas expands adiabatically. The gas in the cylinder keeps expanding slowly, causing damage to its surroundings until its temperature lowers from TH to TL. The process is both reversible and adiabatic if the piston travels frictionlessly and the process is quasi-equilibrium.

(Process 3-4): Reversible isothermal compression: At temperature TL, the cylinder is placed in contact with such a heat sink. An external force pushes the piston, which then works on the gas. The gas temperature is maintained at TL during compression, as well as the operation is a reversible type of heat transfer. During this operation, the total quantity of heat expelled from the gas’s heat sink is QL.

(Process 4-1): Reversible adiabatic compression: This heat sink is removed and the gas is squeezed adiabatically. Until the temperature of the gas increases from TL to TH, the gas inside the cylinder remains compressed slowly, receiving work from its surroundings. The cycle is completed when the gas returns to its normal condition.

The status of the gas has been restored to its original state at the end of the fourth step and the cycle could be repeated as many times as desired. The gas has created work W during the cycle and the quantity of work is equivalent to the size contained by the process curves. The quantity of work created is equal to net heat is transferred throughout the operation, according to the first rule of thermodynamics:

W = Q1 – Q2

The Carnot cycle functions as an engine, turning heat transferred towards the gas during the operations into usable work. An Otto cycle illustrates how internal combustion works, whereas a Brayton cycle shows how well a gas turbine engine works.

Principles of Carnot cycle

The heat engine is a reversible thermodynamic efficiency if all of the processes that constitute the cycle are reversible processes. Otherwise, it’s a heat engine that can’t be turned off. Unfortunately, because no reversible mechanism exists in nature, most heat engines were irreversible in practice.

The second law of thermodynamics results is known as the Carnot Principles. They’re written like this:

An irreversible heat engine’s efficiency is always lower than a reversible one running between two liquids. Every reversible heat engine working between the same two liquids has the same efficiency.

The Carnot cycle has a variety of applications

One of the uses of this cycle is thermal devices and thermal machines. A few examples are:

• Heat pumps for heating.

• Freezers for cooling.

• Steam turbines in ships.

• Combustion engines in combustion vehicles.

• Aircraft reaction turbines.

 Carnot cycle’s effectiveness

The Carnot cycle is reversible, denoting an engine cycle’s maximum efficiency. Because natural engine cycles are irreversible, they have a substantially lower efficiency than Carnot while operating at the same temperatures. The addition and removal of the fluid inside the cycle are aspects that determine efficiency. The Carnot cycle achieves optimum efficiency because all of the heat is sent to the fluid at its highest temperature.

Note: Carnot engine is an ideal circumstance in which it establishes a limit even though it is impossible to create in everyday life. When a real engine is built, the objective is to make it as flawless as possible to be as efficient as feasible. Another device, similar to the Carnot engine, is a refrigerator.

Conclusion

All cycles trend toward the Carnot cycle, which is the ideal cycle. The maximal adiabatic thermal efficiency can be attained by reaching the isothermal contraction and extension of the Carnot cycle or through inter-cooling in compression and warming in the expansion process. The Carnot cycle has the highest engine efficiency (even though other cycles have the same efficiency) because it is based on no wasted processes, including friction and no heat conduction between various engine sections at various temperatures.