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Questions tagged [carnot-cycle]

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Why an ideal gas expands in the 2nd step of carnot's cycle/engine?

In the 2nd step of carnot's cycle, when the gas cylinder is kept under an adiabatic condition, it expands and the temperature falls. My question is why does the gas spend it's internal energy to ...
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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 ...
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Efficiency of a reversible thermodinamic cycle

1 mole of ideal monoatomic gas completes a reversible ABC cycle, in which AB is a VOlume constant tranformation, BC an adiabatic expansion(Q=0) and CA an isotherm(Temperature during tranformation is ...
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Efficiency of Carnot engine [duplicate]

Why is the efficiency of Carnot engine regarded as the maximum efficiency possible for a heat engine?
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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 ...
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402 views

Plotting isothermals and adiabats

first time poster in this site. I am trying to create a small program to make a graph of the Carnot cycle. For isothermals I am simply trying to look for points where P*V would give the same ...
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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: ...
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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 ...
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385 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 ...
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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 ...
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398 views

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 ...
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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 ...
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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 ...
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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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Why a reversible engine's efficiency must be equal to that of a Carnot engine

Apparently, in order to prove that an engine must be as efficient as a Carnot engine if reversible is because apparently for its efficiency in either direction: $\eta_E \le (1-T_2/T_1)$ $\eta_R \ge (...
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Clausius's Carnot Cycle Equation Derivation

In his paper clausius describes a Carnot cycle and he continue arguing like below: In order to make an analytical application of the method...we will assume that all the changes which the gas ...
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226 views

Why is there Net Work Done on a Pressure/Volume Cycle?

The area enclosed by the rectangle is said to be the Net Work Done. My question is why would there be any net workdone if it returns to its initial position (W). Shouldn't it act like a force-...
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66 views

Can you calculate the supplied heat given a p(V) - Diagram of a isobar process?

You are given an p(V) - Diagram like this: Source: How to calculate the efficiency from a $p$-$v$ diagram? There you see two isothermal processes and two isochor processes. For every given ...
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Where does the energy come from for adiabatic processes of a Carnot cycle?

I'm getting stuck on where this additional energy comes to move the piston further outward/inward during adiabatic processes when the only energy changed is during isothermal processes. Can someone ...
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Why can't we make Carnot heat engine in real life?

Question is obvious: Why can't we make Carnot heat engine in real life? I read Wikipedia and Fundamentals of Physics (Halliday) but I didn't found anything about my question. there we're explanations ...
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1answer
372 views

Carnot Engine - Maximum Efficiency Proof?

As an introductory physics student (independently studying before my return to official classes this summer), I am given a "proof" that the Carnot engine has the maximum efficiency possible by way of ...
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392 views

Why does there need to be an isothermal compression in a Carnot cycle?

This is the part that allows the Carnot engine to not violate the 2nd law of thermodynamics, but, hypothetically, why can't we just adiabatically compress the working substance to get it back to State ...
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1answer
202 views

Why is there a cold reservoir in a Carnot engine?

I'm trying to wrap my head around the idea behind a Carnot engine. The main question I'm trying to figure out is how a Carnot engine actually works in producing work. I'll provide a picture for ...
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Deriving the second law of thermodynamics from an irreversible carnot process

I have studied the ideal carnot cycle extensively where we assume that $$\Delta S_{\mathrm{total}}=\sum_i \frac{Q_i}{T_i} =0$$ Now I was wondering whether it is possible to derive basic properties ...
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1answer
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Limitations of converting pressure into kinetic energy

Bernoulli's principle states that an increase in the kinetic energy of a fluid occurs simultaneously with a decrease in pressure for isentropic processes. What then limits us from converting all of ...
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How do I prove that the Carnot cycle is the most efficient graphically? [closed]

I have to prove that the Carnot cycle is the most efficient by comparing it with a arbitrary cycle working within the temperature range of $T_L$ to $T_H$ in a ST-diagram. How do I do this?
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Irreversible heat engines strictly less efficient than reversible ones

I understand how Carnot's theorem implies that irreversible heat engines must be no more efficient than reversible one's, but it is less clear why they need to be less efficient, as I have seen stated ...
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1answer
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Entropy generation in an endoreversible engine

An endoreversible engine is one that is internally reversible (i.e., a perfect Carnot engine) but the heat transfers occur across imperfect conductors (resistances), thus rendering the engine ...
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Why is the net entropy change of an irreversible engine positive?

In a Carnot engine the net entropy changein a cycle is zero. But in an irreversible engine operating between two temperatures the net entropy change in a cycle is positive. As I have understood, this ...
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How is the work done by Carnot Engine obtained or converted to usable form?

I read about the Carnot Cycle and Carnot engine where it was said that the work done by this engine is equal to the area enclosed in the PV diagram. I understood the proof and everything but I am not ...
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Efficiency of a Carnot machine, in which, some of its extreme points are in the region of liquid transition to steam

I need to calculate the efficiency of a Carnot machine, in which, some of its extreme points are in the region of liquid transition to steam with the works, differences of energy and heats of each ...
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1answer
96 views

Carnot's Engine Proof flawed?

https://www.youtube.com/watch?v=LUoUb4hGMH8 I was looking at the reason as to why a Carnot Engine and watched this video on KhanAcademy. He used a very clever method of proving this by using the ...
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64 views

Thermodynamic cycles

Consider a system that takes excess air (assume it to be an ideal gas, $Cp = \frac{7}{2} R$) from a power plant stack at $370 \rm K$ (typo in figure) and $2$ bar and compresses it to 20 bar ...
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Does chaining Carnot heat engines make them more efficient?

Since the efficiency of a Carnot cycle depends on the difference between the hot and cold sides of the engine, could you put multiple heat engines in a series to maximize overall efficiency? A $3000 \,...
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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 ...
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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 ...
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228 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 ...
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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 ...
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1answer
1k 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 ...
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142 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 ...
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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 ...
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1answer
303 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 ...
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1answer
243 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 ...
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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 ...
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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 ...
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Why is the entropy of a Carnot engine always constant?

I am 99% sure that I am wrong here, but here is my reasoning. The efficiency of a Carnot engine can be written as: $$ \eta_{carnot} = 1 - \frac{T_f}{T_i} $$ But since Effency's definition says $\...
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Why can't a Carnot engine heat sink be at absolute zero? [duplicate]

We know that for a Carnot engine the efficiency is given by $1-(T_2/T_1)$, but why can't a real engine have $T_2=0\,{\rm K}$? I know that the efficiency cannot be $1$, but why can't we make the heat ...
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402 views

Is the efficiency of a reversible heat engine independent of the processes involved?

Does the following question conflict that fact that efficiency of a reversible engine is independent of processes involved?
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228 views

What makes a process reversible?

I just want someone to verify what I think. I originally thought that for a reversible process to occur, no irreversibilities like friction can occur. Nevertheless, if we consider the Carnot ...
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Does the thermal efficiency depend on the reversibility of the engine when isochoric or isobaric processes are involved?

I'm confused on the efficiency of a thermal engine (with an ideal gas) in the case in which it is reversible or not reversible, in particular where the ideal gas follows isochoric or isobaric ...