Questions tagged [carnot-cycle]

A theoretical ideal thermodynamic cycle which provides an upper limit on the efficiency that any classical thermodynamic engine can achieve during the conversion of heat into work, or conversely, the efficiency of a refrigeration system in creating a temperature difference by the application of work to the system.

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Efficiency of thermal (rankine) power plants based on ambient temperature?

so I'm preparing for an interview and this is a common question that they always ask, Say there are two power plants working on ideal rankine cycle One in Alaska (low ambient temperature) and one in ...
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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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Confusion about forces in the work done on the piston by the gas in Carnot cycle

I was drawing a free body diagram of the 3rd step of the Carnot cycle as shown below. The forces with - sign are reaction forces to the forces without the sign, according to Newton's 3rd law of ...
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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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Relation between heat quotient and temperature quotient

Is $$\frac{Q_c}{Q_h} = \frac{T_c}{T_h}$$ valid for any reversible ideal cycle Or just for the Carnot cycle?
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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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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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What does the ratio of reservoir temperatures have to do with the efficiency of a heat engine?

I am having a conceptual difficulty with heat engine efficiency. I do not understand why having a larger difference in temperature between the hot and cold reservoirs have an effect on the thermal ...
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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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Application of Stokes theorem in closed thermodynamic cycles

I was reading a book on thermodynamics when I came across the following: "Any closed thermodynamic cycle can be approximated by infinitely many Carnot cycles". I realize that because the ...
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Can the Efficiency of an Arbitrary Reversible Cycle be Equal to the Efficiency of the Enclosing Carnot Cycle?

I was reading the following article: https://www.researchgate.net/publication/...
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Why do we need an adiabatic expansion in the Carnot cycle? [duplicate]

As we know that 1st process is an reversible isothermal expansion during this the system is in quasi static equilibrium which helps in increasing the volume of the system but why does the second step ...
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Is there a specific commercial or experimental implementation of the Carnot cycle? [closed]

I have been unable to find an example of a Carnot engine implemented practically, beyond the drinking bird (which has not revolutionized technology as far as I know). I understand the Stirling and ...
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How does Heat flows in Carnot engine? [duplicate]

According to fundamental concept of thermal conduction, heat flows from higher temperature to lower temperature. As in Carnot cycle, there is isothermal expansion and compression as a process i.e. ...
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Reversibility of the ideal Carnot cycle

How do adiabatic processes in the reversible Carnot cycle take place? Is the gas adiabatically isolated? If so, how would that happen in real life? (I know that Carnot cycle is not practically ...
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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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How to derive the Clausius Inequality?

In my thermodynamics class, we've seen the Clausius inequality derived for a Carnot cycle, and then extended to any cycle. For the Carnot Cycle, we have that it's the most efficient possible cycle ...
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Why does the temperature of the working fluid have to be close to the temperature of the cold reservoir during a Carnot cycle?

I understand why the temperature of the hot reservoir has to be minimally higher than the temperature of the hot working fluid during the isothermal expansion phase of the Carnot cycle (to limit new ...
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Work obtained during isentropic expansion in the Carnot cycle versus the work done to gradually lower the outside pressure

We have a Carnot cycle and lets say it is in thermal and mechanical equilibrium with the surroundings before the beginning of the process. I am using the convention that heat brought to the system is ...
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In a Carnot Engine, how does the heat flow from the heat reservoir to the engine if both are at the same temperature?

From what I read about the Carnot Cycle, there are 4 major steps involved, viz. Isothermal Expansion, Adiabatic expansion, Isothermal compression and Adiabatic compression. During the Isothermal ...
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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 efficiency among any other engine cycle, however I never found a convincing proof for it. Wherever I have put this ...
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Relationship between volume and temperature of an ideal gas

I am self-studying thermodynamics, and was reading up Carnot heat engine (Yunus Cengel - thermodynamics book). So, the experiment in the textbook is set up such that, we have an adiabatic piston-...
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Carnot cycle with finite heat capacity [closed]

Suppose we perform a Carnot Cycle between 2 temperature baths $T_1$ and $T_2$ with $T_2>T_1$ and both having finite heat capacity $C$. What is the final equilibrium temperature? I have a vague ...
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Where is the heat loss occuring in the Carnot cycle, if compared to a ideal gas turbine

The most efficient heat engine cannot be more efficient than this (1 - tc/th) so let's assume a hypothetical gas turbine where there is no friction or conduction losses , say the ambient temp is 300k ,...
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Is there a thermodynamic cycle used where energy is extracted when the gas condenses to a liquid?

I was trying to calculate the energy efficiency of such a cycle, but I'm not sure how it depends on the input and output temperature difference, which doesn't seem right. The cycle I was thinking of ...
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Thermodynamic temperature scale

I was wondering why is it that I can replace heat going into a carnot engine with the temperature of the "hot place" and vice versa, i.e , why can the temperatures of the places replace the ...
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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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Temperature Dependence of Thermal Efficiency in Carnot Cycle

Suppose a Carnot Cycle operates between a hot reservoir at temp $T_h$ and a cold reservoir at temp $T_c$. Suppose also that the system is initially at point $(V_1,p_1)$ in the pV-plane and that the ...
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Generalizing Carnot theorem

Motivated by question Can IC engines be modeled as Carnot engines?. I am wondering whether/how Carnot theorem could be generalized to other kinds of devices performing "useful work", such as,...
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Can IC engines be modeled as Carnot engines?

In the "talk" tab for Wikipedia Heat Engine article, someone is questioning whether an internal combustion engine can be modeled as a heat engine - and therefore is limited or is not limited ...
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An alternative approach to proving the Carnot's theorem using the equality of areas of $pV$ and $TS$ diagrams

According to Carnot's theorem, the efficiency of a reversible heat engine operating between two reservoirs at different temperatures is independent of the working substance and depends only on the ...
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Can heat flow from colder to hotter body breaking the second law of thermodynamics? [closed]

In an isothermal process, the whole heat is converted to work but not in a cycle so it doesn't break the 2nd law of thermodynamics. $$dQ=dW$$ But let's imagine a scenario with it. If we connect an ...
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Understanding Clausius theorem by slicing an arbitrary cycle into multiple Carnot cycles

As the title implies, I had some issues understanding how Clausius theorem $$\int_{Closed}\frac{dQ}{T} = 0$$ can be derived for an arbitrary cycle starting by slicing it into multiple Carnot cycles. ...
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Please explain why the Carnot cycle is reversible while the Otto cycle is irreversible using the kelvin or clausius statement of the second law [closed]

why is the Carnot cycle reversible while the Otto cycle irreversible according to Kelvin-planck statement
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Calculation of efficiency of a heat engine [closed]

The efficiency of any heat engine doing work $W = |Q_{in}| - |Q_{out}|$ is given by: $N = |W|/|Q_{in}|$ The reasoning for this given in my textbook is along the lines of: The purpose of any heat ...
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Why is the cyclic volume integral of $P/T$ larger than the one of $P_{ext}/T$ in an irreversible process?

In order to derive the Clasius inequality we can call the first law of thermodynamics in it's differential form: $$dU={\itđ}q-P_{ext}dV.$$ If the process is reversible: $$dU={\itđ}q_{rev}-PdV.$$ ...
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Could Refrigerators Take In Cold Outside Air To Save Energy?

We heat up rooms, then we use that warm air and cool it down in refrigerators. Each is a lossy, energy requiring process. This seems thermodynamically inefficient. Couldn't refrigerators get cold air ...
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How the temperature used in second law of thermodynamics and ideal gas law equivalent? [closed]

I was reading Theory and Problems of Thermodynamics by Schaum's Outline series and there the author starts from some axioms (which are the thermodynamic laws, excluding the zeroth and third). Then he ...
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Why does heat engine efficiency use absolute zero rather than thermal differential?

Carnot's theorem calculates efficiency of a heat engine versus absolute zero. I read the question Why can Carnot efficiency only be 100% at absolute zero? But I don't feel it addresses it precisely. ...
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Why does adiabatic contraction bring Carnot engine back to initial state? (and other questions) [closed]

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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What is Entropy Balance Relative to (un)Compensated Heat of Clausius?

Consider the ideal Carnot cycle consisting of two ideal reversible isothermal stages at $T_0$ and $T_1$ and two ideal adiabatic reversible (isentropic) stages connecting them; assume that $T_0 > ...
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Why adiabatic expansion happens in Carnot cycle?

$A \rightarrow B$: Isothermal expansion happens. Since the internal energy purely depends on the temperature ($E_{int} = knRT$, $k = \frac{3}{2},\frac{5}{2},3$), then $\Delta E_{int}=0$ in an ...
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How can we say that work done by carnot engine in a cycle equals net heat released into it even when it is operated b/w 2 bodies and not 2 reservoir?

When a carnot engine is operated between 2 reservoir then after each cycle it return to its initial state so change in internal energy is zero and so work done by it equals net heat released into it. ...
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How does a reversible Carnot cycle transform heat to work?

To make clearer what I am asking let me introduce a new terminology to avoid any misunderstandings. Let the heat flow, which is rate, between a reservoir and an engine be denoted by $\mathfrak J$ and ...
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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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Carnot Cycle Question

I have two questions surrounding the Carnot cycle. The typical diagram for a Carnot cycle is shown here: I have several textbooks that discuss this cycle, but what none of them do is explain how ...
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Optimality of the Carnot cycle

It is well-known and is stated always and everywhere that the Carnot cycle is the most efficient thermodynamic cycle. Although stated as such it is rarely proven. One proof is in the article "...
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Carnot engine (theorem) proof

I am facing issues in the proof. Some links to the proof of carnot engine: https://en.wikipedia.org/wiki/Carnot%27s_theorem_%28thermodynamics%29 https://www.khanacademy.org/science/physics/...
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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, ...
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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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