Questions tagged [carnot-cycle]

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Is freezing water a carnot cycle?

Freezing water is a reversible process, but how do we know if it could be interpreted as a carnot cycle?
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Is it always true that a non-adiabatic reversible process is an isothermal process?

In a Carnot Cycle, a reversible isothermal process is a non-adiabatic reversible process. Is it always true that a non-adiabatic reversible process is an isothermal process?
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Steam flow direction through valves - Watt Engine

I don't have a background in Thermodynamics. I am trying to understand a paragraph from the book - Einstein's Fridge. The author says that when the piston is near the bottom of the cylinder, and the ...
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1answer
37 views

What is the need of adiabatic compression in Carnot cycle?

Why do we need to compress the gas adiabatically after the isothermal compression of gas? What if we just skip this step? What will be the consequences? By "skipping this step",I mean, after ...
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5answers
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Why is it necessary for a heat engine to work in cycles?

We can make a steam engine just by putting huge amount of water in large tank and heat it and then use the steam to run the wheel. We just have to put huge amount of water and heat then engine will ...
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Why don't we really consider the TOTAL (SYSTEM +SURROUNDINGS) entropy change in Carnot cycle?

During a Carnot cycle, why don't we consider the increase in entropy of surrounding by the energy given to surrounding via work done by gas piston? I mean we want to find the total entropy change then ...
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1answer
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Why is entropy of gas reamains constant during adiabatic expansion?

In adiabatic compression, we add energy to the gas via piston and decrease volume. Now the increase in energy and decrease in volume will cause increase and decrease in entropy respectively, but it ...
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1answer
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Modified Carnot engine example requiring clarification regarding Clausius' Theorem and Second Law of Thermodynamics

If we introduce a finite temperature difference between source/drain and that of the working fluid in thermal contact, we would make the process irreversible since the direction of heat flow cannot ...
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1answer
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Can we show that the “Carnot cycle is the most efficient cycle in ideal gas” without using any form of the Second Law?

My Question: Is it possible to show that the Carnot cycle is the most efficient cycle in an ideal gas without using any form of the Second Law of Thermodynamics? Also. If this is possible, how can we ...
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What's the pressure of surrounding of carnot cycle? [closed]

Is it always equal to changing pressure of cylinder? How is it possible?
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Is efficiency of Carnot engine dependent on temperature of heat source/sink?

Suppose we are working with a Carnot engine. In this engine, temperature of the heat source is say $373K$ and that of heat sink is say $293K$. Now, the initial temperature of the gas(ideal) is 333K. ...
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Volume Ratio of Carnot Engine

Consider a Carnot engine operating between a hot reservoir with temperature 700 °C and a cold reservoir with temperature 70 °C. The engine contains 0.13 mol of gas, and outputs a net 630 J of work. ...
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Change in entropy of engine and the hot bath in a cycle

I want to clarify that this question is not a homework-type question. I have provided its solution and the apparent discrepancy. This is a question from a national competitive exam I gave. I am very ...
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Reconcile different definitions of temperature

In classical thermodynamics, one way to define the temperature is to measure the efficiency of the Carnot cycle, i.e. $$w = 1-\frac{T_c}{T_h}$$ And in some other texts (like in the statistical ...
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Can heat transfer from one object to another if they both have the same temperature?

I do not understand how the heat is transferred between the reservoir and the gas in stages 1 and 3 of the Carnot Cycle (the isothermal parts of the cycle). From what I know, If two objects have the ...
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Carnot's engine

Why do we use isothermal process in Carnot's engine? I think it should be isobaric process, because when we heat the gas it goes expanding to keep the pressure constant. Why is my thinking wrong?
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What does “entropy” really mean?

I'm currently taking a course of introduction to biophysics in college and we currently covered a subject called entropy (S). We did some maths based on the Carnot cycle and came up with the following ...
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Meaning of “Heat engine working between two Temperatures”

According to Carnot Theorem: "Of all engines working between two given temperature, none is more efficient than a carnot engine." I want to know what actually is meant by an engine working ...
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Theoretical efficiency of a laser

A laser produces a coherent, collimated light beam. This is like a less-disordered version of the light from say a light bulb. When I learned about heat pumps in thermodynamics class, I found that we ...
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$p$-$V$ Diagram of a real chiller (fridge, heat pump, …)

I am struggling to find a $p$-$V$ Diagram of a real (not CARNOT!) heat pump. Regarding engines (diesel, otto) this seems to be an easy task but I am failing to do so for heat pumps. Could anyone help ...
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Carnot cycle total reversibility

I read the discussion of the same problem in another problem posted here Carnot Total Reversibility, but still I can't get the reason why Carnot cycle is stated as "Totally Reversible", it ...
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1answer
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Adiabatic expansion vs. adiabatic compression in Carnot cycle

I am currently studying the Carnot cycle, and am close to understanding it, but something is nagging on my mind. So, during the expansion process of the cycle, work is done on the surroundings as heat ...
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2answers
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Is Carnot cycle the only “most efficient” cycle? [duplicate]

In all the books, that I have studied so far, they say that Carnot cycle is the most efficient cycle. But why isn't any other reversible process as efficient as Carnot cycle? Can somebody please ...
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Confusion with Carnot Cycle Problem

Consider two fluids $F_1$ and $F_2$ with equal volume and heat capacity as well as $T_1$ and $T_2$ respectively, whereby $T_1 > T_2$. One uses a Carnot cycle to transfer heat from $F_1$ to $F_2$ in ...
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1answer
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Why Doesn't Thermal Radiation Render Thermionic Conversion Unable To Approach Carnot Efficiency?

Thermionic Conversion follows the classic Richardson-Dushmann Equation for thermionic current as a function of temperature squared: $$J_{RD} = A_0 T^2 \exp\left(-\frac{\phi}{k_B T}\right)$$ where $J_{...
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Why does adiabatic contraction bring Carnot engine back to initial state? (and other questions)

I have many questions (all in bold) around the Carnot cycle. I know I'm not the first one to ask a bunch of questions in the middle of a description of my own understanding, but having read other ...
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Why does $\oint\frac{\delta Q}{T} = 0$ when evaluated over a Carnot cycle?

In my thermodynamics schoolbook, it is asked to apply the Clausius inequality to a Carnot cycle. According to the book the answer is to evaluate $\oint\frac{\delta Q}{T}$ over the cycle which should ...
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1answer
85 views

Carnot heat engine at maximum power

I am trying to prove that the Carnot efficiency for a heat engine with maximum power is $1-\sqrt{\frac{\tau_l}{\tau_h}}$, where $\tau_h$ is the high temperature, $\tau_2$ the lower temperature, and we ...
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How to find efficiency of a cycle thats not Carnot Cycle?

Here is the Full Question: A monoatomic gas is expanded adiabatically from volume $V_0$ to $2V_0$ and then is brought back to the initial state through an isothermal and isochoric process respectively....
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1answer
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Why is this equation valid in the carnot cycle? [closed]

I'm following a derivation here of a carnot-cycle and I'm stuck at $ T_3 / T_1 = T_4 / T_1 = (V_1 / V_4)^{(κ - 1)} = T_3 / T_2 = (V_2 / V_3)^{(κ - 1)} $ I don't get that. Is that due to ...
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2answers
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Carnot cycle doubt

I am trying to solve a carnot cycle numerical, where I encountered a concept doubt. When heat is absorbed from the heat source/higher reservoir during first isothermal expansion, does the temperature ...
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1answer
488 views

Isothermal irreversible expansion of ideal gas

I am studying Thermodynamics in my first year and I don't quite understand the process of isothermal reversible/irreversible expansion. Below is a P-V graph I found on Google, just to help me ...
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How to explain from the second law that absolute zero cannot be attained?

How can we explain from thermodynamics that the absolute zero of temperature cannot be attained? I was thinking along the following lines. The efficiency of Carnot engine $\eta=1-\frac{Q_2}{Q_1}=1-\...
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1answer
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Proof for $\oint \frac{dQ}{T}=0 $ in a reversible process

I'm actually trying to prove that Entropy is a state function. I get struck at the point where I need to prove that $\oint \frac{dQ}{T}=0 $ for a reversible process. Clausius in his book The ...
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How can we show that Entropy is a State Function?

Intro: Thank you for reading. I know there are lots of questions on Stack Exchange about entropy. The following is the one that most closely addressed my confusion: Entropy as a state property ...
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Why only isothermal and adiabatic for Carnot engine?

What is the reason behind choosing adiabatic and isothermal process for carnot engine? My book states the following reason. I am not able to understand it. It would be great if you could put it in ...
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154 views

In the isothermal expansion phase of a Carnot cycle, why does the gas expand?

Descriptions of the isothermal expansion in a Carnot cycle typically say heat is absorbed by the gas and the gas expands. But why would it expand? The heat reservoir keeps the temperature constant, ...
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The reversible Carnot cycle is the most efficient between $T_2$ and $T_1$. Is it a form the second law itself?

The second law of thermodynamics proposed by Clausius, Kelvin, Carnot ..etc in its original form as T dS> dQ for irreversible process and Tds =dQ only for reversible thermodynamics process. This ...
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Apparent contradiction concerning the net work of a Carnot cycle

The net work of a Carnot cycle, $W$, is $$\tag{1}W=Q_{h}-Q_c.$$ This work also satisfies $$\tag{2}W=Q_{h}\bigg ( 1-\frac{T_c}{T_h} \bigg )$$ Let us fix $Q_{h}$, the amount of heat initially ...
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Deriving $Q_{1}-Q_{2}=W$ for a perfect gas that had gone through a Carnot cycle

I saw multiple times that if an engine, say Carnot engine, absorbs heat $Q_{1}$ at $T_{1}$, does work $W$, and expels heat $Q_{2}$ at $T_{2}$, then we should have$$\tag{1}Q_{1}-Q_{2}=W.$$ Let us say ...
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How do I use calculus of variations to prove that Carnot cycle is the most efficient one?

There are already many questions on Physics SE asking for a proof of the maximum possible efficiency of Carnot's engine. However, none of them (at least the ones which I looked up) contain a ...
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Why does the gas compress during isothermal compression, in the carnot cycle

In this step, the gas is said to release some heat dq. From where does energy come from? The temperatures are the same, so internal energy won't flow. But the gas compresses, hence the change in ...
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About the adiabatic stroke in the Carnot cycle

I understood that in the adiabatic stroke, the internal energy is being used up to do work Again, assuming that the internal energy of all the gas molecules of the system are the same (can we?) Why ...
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Can anyone prove this overstated-but-almost-never-justified fact from thermodynamics?

Clausius inequality states that $\oint {\delta Q\over T}$ equals zero for a system undergoing a reversible cycle, whereas it can’t be greater than zero for an irreversible cycle. But everywhere, I ...
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Efficiency of heat engines

I have been taught that the an engine running on the Carnot's cycle has the maximum energy among the maximum efficiency, however I never found a convincing proof for it. Wherever I have put this ...
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Efficiency of sequential Carnot engines [closed]

A Carnot engine A operates between temperature $T_1$ and $T_2$ ($T_1>T_2$). A second Carnot engine B uses all the heat rejected by A as input and input and operates between temperature $T_2$ and $...
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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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197 views

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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1answer
229 views

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: ...