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Better understanding the Clausius Inequality

My conceptually understanding draws on the section on the Clausius Inequality from Finn's Thermal Physics. Attached is the graphic used for the derivation in the textbook. If I'm to understand ...
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1answer
49 views

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 ...
0
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1answer
50 views

Source and sink in an ideal reversible otto cyle?

what the temperature of source and sink is in an otto cycle? Since the temperature of the surroundings continuously change during the isochoric parts, we cannot have a single source and sink ...
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2answers
64 views

Efficiency of reversible carnot engine must be 0?

In order for heat to transfer in a reversible process, the temperature difference must be approximately zero. Therefore at the isotherms in a carnot engine, there is negligible temperature difference. ...
1
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2answers
360 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 ...
1
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1answer
238 views

Can you plot an irreversible cycle on a PV diagram?

You can only plot reversible processes in PV diagrams. And I suppose a cycle made of reversible processes should be reversible (am I right?). So every cycle plotted in a PV diagram should be ...
0
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3answers
136 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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1answer
120 views

$\sum{\frac{Q}{T}}$ is zero

I was going through a proof in my book and couldn't understand the last part of the proof. I mean I understand $$\frac{Q_1^{\prime}}{T_1}-\frac{Q_2^{\prime}}{T_2}\leq 0$$ But after that how did ...
1
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0answers
109 views

Does negative absolute temperature imply heat engine efficiency greater than one?

As it is shown in Prove that negative absolute temperatures are actually hotter than positive absolute temperatures, a body with absolute negative temperature is hotter than a body with any absolute ...
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1answer
3k views

Derive the Carnot Efficiency without using the Carnot Cycle? [closed]

How can you derive the Carnot efficiency using only properties of reversible cycles?
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1answer
188 views

Reversible engines

As far as my understanding goes, the only reversible heat engine is the Carnot engine, described by the Carnot cycle. On the other hand, in all of the resources I've found the change in entropy for ...
8
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3answers
596 views

How heat flow through finite temperature drop is an irreversible process?

Is it necessary that the drop/rise in temperature by flow of heat is irreversible?
2
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1answer
387 views

Prove all reversible heat engines that work between just two temperatures have the same efficiency

Can someone explain this explanation to me: A completely different argument focuses on the requirement that the device only move heat at one or other of the two temperatures. Then, provided we ...
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4answers
509 views

Does a reversible heat engine exchanging heat with an ideal gas that does a transformation imply that transformation is reversible?

Consider a reversible heat engine working between two sources. Suppose that one of the sources is a thermostat, while the other is an ideal gas which follows a transformation and exchanges some heat ...
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2answers
534 views

Question about reversible heat engine efficiency

I have a question regarding heat engines that cropped up whilst I was doing a practice question. I will summarise the results I obtained for the previous parts of the question so as to save your time. ...
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2answers
7k views

Efficiency of reversible engines

I'm a little confused about something. All reversible engines have the same efficiency, or one could drive the other to move more heat in the reverse direction. Also, no engine has an efficiency ...
6
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4answers
4k views

Why is it that a Carnot heat engine will reject no heat to a zero temperature sink?

Looking at the equation for Carnot efficiency, I notice that as the temperature of the heat sink approaches zero, the efficiency approaches unity: $$ \eta_{rev} = 1 - \frac{0}{T_H} = 1 $$ Seeing ...