# Questions tagged [carnot-cycle]

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### How does the Carnot Cycle work?

I am learning the Carnot cycle, which consists of four transformations for a fluid. In the first two transformations the volume of the fluid expands, generating work. This happens in two steps: ...
2answers
151 views

### About the 2nd Carnot Corollary

I have a question about the 2nd Carnot Corollary. According to Moran, Fundamentals of Engineering Thermodynamics, the 2nd Carnot Corollary stated that "all reversible power cycles operating between ...
3answers
375 views

### Why doesn't the water cycle stop, since it dissipates energy?

In artificial cycles like for example refrigeration cycle, because of irreversibilities extra energy is require to be provided so that the refrigerant is available at the same state as it was at the ...
2answers
203 views

### Example of a Carnot machine made of a different physical system than a ideal gas?

Anybody knows an example of a Carnot machine made with any different thing than a gas? For example wire or a magnet. I was wondering that since I read the Kardar's book on Statistical Mechanics. He ...
1answer
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### Validity of Carnot's theorem when operating between finite reservoirs

Carnot’s theorem tells us that "the most efficient heat engines operating between 2 reservoirs have the same efficiency as a Carnot engine". This theorem assumes that the engines are operating ...
2answers
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### Calculating efficiency of a Engine

Given are four points in a PV-diagram: $(V_1, 3/2P_1)$ is the leftmost point, $(V_2,3/2P_1)$ is the rightmost point, $(\frac{V_1+V_2}{2},P_1)$ is the lowest point and $(\frac{V_1+V_2}{2},2P_1)$ is the ...
2answers
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### Why is the Peltier / Seebeck Effect's efficiency so low in practical devices?

Usually solid state devices are able to attain excellent efficiency. However, currently existing Peltier coolers and Seebeck generators have horrible efficiency -- far worse than Carnot, and also far ...
2answers
78 views

### Thermodynamics problems with a cycle (insufficient data?)

I am having some troubles in solving the following problem a professor gave us, and in my opinion I think that either there are insufficient data or the solutions are infinite. We have a perfect gas,...
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### Total Reversibility of Carnot Cycle

I was reading about Carnot cycle in "Thermodynamics by Cengel & Boles", now it is stated that Carnot cycle is a totally reversible cycle, i.e it is an internally as well as externally reversible ...
1answer
104 views

### Carnot cycle with varying reservoirs

I was thinking what will happen to the standard Carnot cycle, if instead of - say - the usual cold reservoir, we adopt a smaller refrigerator, whose temperature in fact changes after the heat release ...
2answers
371 views

### Could a Carnot engine linked to a Carnot “refrigerator” create a perpetual heat flow between two reservoirs?

Here is a diagram of the system in question (adapted from the diagram on this page): All of the work produced by the Carnot engine is used to drive the Carnot refrigerator, which is simply a Carnot ...
1answer
219 views

### Actual sequence of refrigeration cycle

Whenever i have studied refrigeration cycle on books, i have found that the diagrams are always explained starting from the compressor*, then condenser then throttle and finally evaporator. I find it ...
1answer
3k views

### Calculating the maximum efficiency of an engine cycle

I'm a little confused about calculating the maximum efficiency of an engine cycle. From what I've learned the carnot cycle is connected by two adiabatic processes and two isothermal, and this is the ...
1answer
619 views

### How is isothermal expansion/compression physically possible when it assumes heat flow between equally hot bodies?

An ideal Carnot engine is composed of two reservoirs and a working fluid. The hot reservoir and the cold reservoir have temperatures $T_1$ and $T_2$ respectively, with $T_1>T_2$. The working fluid ...
1answer
988 views

### Reversible and irreversible cycles: Changes in entropy of the system and the surrounding

Entropy is a state function. Is it true that at the end of a cyclic process, the change in entropy of the of the system and that of its surrounding are both separately zero irrespective of whether ...
3answers
137 views

### Is there an implemented example of an almost reversible heat engine?

I'm reading Feynman's discussion of Reversible engines (Vol I 44.3) in The Feynman Lectures on Physics. His discussion is very abstract, and leaves a lot of practical questions unanswered. Rather ...
2answers
226 views

### Heat transfer in the isothermal expansion in the Carnot cycle

Problem In the Carnot cycle there are two adiabatic and two isothermal processes. This question focuses on the isothermal expansion. In the isothermal expansion books often writes that the system is ...
1answer
277 views

### Why does the Carnot cycle require adiabatic processes specifically?

Why does the Carnot cycle need two isentropic adiabatic processes to move between hot and cold reservoirs? Surely as the only requirement for the Carnot cycle is that it is constructed out entirely ...
1answer
220 views

### How Much Heat Is Absorbed/Rejected By The Heat Engine?

If a heat engine undergoes a reversible cycle consisting of two isobaric processes and two adiabatic processes, what methodology is used to determine how much heat is absorbed or rejected by the heat ...
1answer
373 views

### How do we know that entropy is a state function given by $\delta Q_{\mathrm{rev}}/T$ for any arbitrary (not just reversible process)?

In this video, the professor goes through a "derivation" for entropy using the Carnot cycle, in which he establishes that entropy is a state function for that process. However, he then continues the ...
2answers
725 views

### Prove carnot engine is most efficient

According to Carnot's theorem, Carnot engine is the most efficient engine. I wanted to know its proof. I looked up and I found a proof on Khan Academy in which he used a reverse carnot engine to prove ...
2answers
718 views