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# 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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### Is Carnot theorem applicable to black holes?

As I know, there is a simple method to take almost all $mc^2$ from mass by dropping it to the black hole. Doesn't this violate Carnot theorem? Or does it define the temperature of black hole as very ...
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### "Universality" of Carnot cycles

In his answer to the discussion "Historical view of the second law of thermodynamics as a complete differential" (https://physics.stackexchange.com/q/823281) @hyportnex wrote that: Contrary ...
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### At what stage in the Carnot cycle, does a Carnot engine produce work?

I am currently confused as to how exactly a Carnot engine (ideal engine) produces work. I will explain my current understanding of how a Carnot engine works: A piston containing gas is placed into ...
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### Contradiction in the Carnot Cycle?

The carnot cycle is reversible, because the temperature difference between heat reservoir and fluid is extremely low, so that heat can flow in both directions. Also, the carnot cycle is described as ...
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### What happens if you factor in the energy required to switch between the reservoirs and insulating stand of the Carnot engine?

I'm reading about the Carnot cycle (as a non-physicist!) and much of the focus is on the idealisation around the infinite time needed due to the requirement of only infinitesimal differences in ...
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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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### How to prove the efficiency of Carnot engine is bigger than Otto engine [closed]

I know the Carnot engine has maximum efficiency among all engines from Clausius statement, but how to prove the relationship of these two engines in equation? Thanks. More specifically, the ...
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