What is a Carnot engine?

In summary, during this conversation the topics of Carnot engines, Carnot cycles, heat engines, reservoirs, temperature gradients, refrigerators, and the first two laws of thermodynamics were discussed. The main points include the theoretical perfection and purpose of a Carnot engine, the use of heat flow between hot and cold reservoirs in a heat engine, the four actions of a Carnot cycle, and the concept of a temperature gradient. Other important facts about thermodynamics were also mentioned. The person asking the questions also notes that they find explanations from others to be clearer than those in their book.
  • #1
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Hey everyone,

I was sick when we started this unit. I've been trying to catch up, and need to ask a couple of broad questions.

1) What is a Carnot engine? Or the Carnot cycle? What is it used for ? Why do we can about perfect conditions??

2) When people keep mentioning "reservoirs", in problems, what do they mean?

3) What is a temperature gradient?

4) What is a refrigerator? (If it is different than the everyday appliance). And how do we describe/use it?

5) What are the first two laws? And how are they applied?

And any other important facts about Thermodynamics!

Thank you very much.

(PS - I'm going to read my book as well, as I have not gotten to most of these things in the chapters. But from my experience you guys explain things better than the book so I asked them here!)
 
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  • #2
A "Carnot engine" is a theoretically perfect heat engine where the maximum possible efficiency is achieved. None actually exist.

A heat engine is capable of making two different bodies at different temperatures do useful work merely by allowing heat to flow from hot to cold. THe two bodies are known as "resevoirs."

For a "hot resevoir" think of a large, large tub of hot water (So large that the temperature does not change significantly as a little bit of heat leaves it).

For the "cold resevoir" think of the atmosphere outside; it's something that the heat can flow into.

The carnot cycle is four actions of the piston: isothermal expansion, adiabatic expansion, isothermal compression, adiabatic compression. After one cycle the gas is back to its starting position on the PV graph.

Oops, got to go...
 
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  • #3


A Carnot engine is a theoretical heat engine that operates on a reversible thermodynamic cycle, known as the Carnot cycle. It was developed by French physicist Nicolas Léonard Sadi Carnot in the early 19th century as a way to understand the efficiency of heat engines. The Carnot engine is used to illustrate the maximum possible efficiency that any heat engine can achieve, and it serves as a benchmark for comparing the performance of real engines. It is also used in the development of practical heat engines, such as steam engines and gas turbines.

The Carnot cycle consists of four stages: isothermal compression, adiabatic expansion, isothermal expansion, and adiabatic compression. During the isothermal stages, the engine is in contact with a heat reservoir, which is a large body of material that can supply or absorb heat without changing its own temperature. In the adiabatic stages, the engine is thermally insulated, meaning no heat is exchanged with the surroundings. The Carnot cycle operates between two heat reservoirs, a hot reservoir at a higher temperature and a cold reservoir at a lower temperature. The engine converts heat energy from the hot reservoir to work, and releases waste heat to the cold reservoir.

The reason we care about perfect conditions in the Carnot cycle is because it represents the maximum possible efficiency for a heat engine. In other words, it shows us the best we can do in terms of converting heat into work. Real engines are not able to achieve this level of efficiency due to various factors such as friction and heat loss.

In thermodynamics, a reservoir refers to a large, homogeneous system with a fixed temperature. For example, a lake or a large body of water can be considered a reservoir for heat exchange. In the context of the Carnot cycle, the hot and cold reservoirs represent the heat sources and sinks for the engine.

A temperature gradient is a change in temperature over a distance. It is often used to describe the difference in temperature between two points in a system. In the Carnot cycle, the temperature gradient is important because it determines the direction of heat flow and ultimately the efficiency of the engine.

A refrigerator is a device that uses work to transfer heat from a cold reservoir to a hot reservoir. Unlike the everyday kitchen appliance, a thermodynamic refrigerator operates on a reversed version of the Carnot cycle. It is used to cool down a space or a substance below the temperature of its surroundings.

 

1. What is a Carnot engine?

A Carnot engine is a theoretical heat engine that operates on the Carnot cycle, which is a reversible thermodynamic process. It is a model that was developed by French physicist Nicolas Léonard Sadi Carnot in the early 19th century to explain the maximum efficiency that any heat engine can achieve.

2. How does a Carnot engine work?

A Carnot engine works by using a reversible process, where heat is absorbed from a high-temperature source and transferred to a low-temperature sink, while performing work. This process is repeated in a cycle, and the efficiency of the engine is determined by the temperature difference between the source and the sink.

3. What is the efficiency of a Carnot engine?

The efficiency of a Carnot engine is given by the equation η = (Th - Tl) / Th, where Th is the temperature of the high-temperature source and Tl is the temperature of the low-temperature sink. This means that the efficiency of a Carnot engine is dependent on the temperature difference between the source and the sink, and it can never be 100% efficient.

4. What are the applications of a Carnot engine?

While a Carnot engine is a theoretical model, its principles have been applied in real-life engines, such as steam engines and some refrigeration systems. It also serves as a benchmark for comparing the efficiency of other heat engines.

5. What are the main limitations of a Carnot engine?

The main limitation of a Carnot engine is that it is an idealized model and cannot be achieved in real-life systems. Additionally, it assumes reversible processes, which are not possible in practical situations. The efficiency of a Carnot engine also decreases as the temperature difference between the source and the sink decreases.

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