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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What stops entropy from forming if you extract 100% of heat flow and use it for work?

In a carnot engine you convert 100% of heat put inside the system during the isothermal phase into work. This is the basis of maximum efficiency and makes sure that it is reversible. If you don't ...
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Does the Carnot efficiency apply to photoelectric conversion?

If you consider a black body as energy source and photoelectric conversion at room temperature as the energy receiver. Wouldn't it be possible to: use an ideal prism/diffraction grating to separate ...
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How to justify that Carnot loop for ideal gas is closed on two sides by adiabatic curves?

I'm trying to figure out how to show that the orange curves connecting the two green curves are infact adiabatic: The set up is that I have an ideal gas, and I am searching for the loop when it's ...
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How was adiabatic expansion conceived from the caloric theory perspective? [closed]

Nowadays we say that during the adiabatic expansion stage of the Carnot Cycle the internal energy due to the temperature of the gas gets transformed into work, but Carnot himself supported the caloric ...
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How is a Carnot engine in quasi-equilibrium?

If the reversible isothermal expansion and adiabatic expansion both yield positive work (as the pv diagram indicates), it means that the gas inside the cylinder was compressed before those stages ...
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Entropy change in each step of Carnot Cycle

How to go about calculating the entropy change in each step of a Carnot Cycle given only $T_{h}$, $T_{l}$, and the work performed per cycle?
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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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What is the energy loss in the first process?

Suppose we have two objects with different temperatures. If we make them contact each other, they will reach the same temperature. However, if we set up a Carnot engine between them, they will also ...
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Entropy change in a Carnot cycle

The Carnot cycle is a reversible cycle, which means that by the end of the cycle the system is in it's initial state, which is characterized by the same entropy value. Therefore we can say that for a ...
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The Work Done by an Irreversible Carnot Cycle

This is a question from the book, Understanding Non-Equilibrium Thermodynamics by Lebon and Jou. Show that the work performed by an engine during an irreversible cycle operating between two thermal ...
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Comparing a gas turbine (Joule cycle) to the Carnot cycle?

My understanding of gas turbines is as follows: When you spin an impeller, you can compress air (this requires work) and when compressed air is expanded, it can be used to spin a turbine (this ...
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Why are the pressures in the Joule-Thompson effect the same before and after?

I understand the Joule-Thompson effect and the mathematics behind it that results in the Enthalpy, $H$, remaining constant. However, one thing I conceptually fail to grasp is why the pressure on gases ...
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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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Power required by a carnot refrigerator [closed]

Problem Statement A car interior is found to be too hot, so an air conditioner is used that operates as a Carnot cycle refrigerator between outside temperature $T_h$ and a lower temperature interior $...
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Approximation of any reversible process by carnot cycle

While studying thermodynamics i came across the fact that any reversible cycle can be represented by series of miniature carnot cycles. I am unable to understand how can it be done for every cycle as ...
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Does $W_{out}$ in gas turbines refer to the shaft or the blades?

I was studying the Bryton cycle for a gas turbine and a question came to my mind about the turbine work output. That is, are we talking about the work output for the turbine blades or about the work ...
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What's the relationship between the Carnot Cycle and Hurricanes? (and more)

I'm trying to understand the relationship between the Carnot Cycle and Hurricanes. My understanding thus far is that the Carnot Cycle follows 4 stages: 2 Isothermic (same temperature) and 2 Adiabatic (...
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Generally will the power output from a heat engine increase as the work from this engine increases?

Generally speaking, does increasing a heat engine's work will essentially increase the power output? Whether this heat engine was a turbine, vechile or whatever.
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In Isothermal expansion of Carnot Cycle, Energy of the system should be constant, Since Temperature is constant. How does the system absorb energy?

In Carnot cycle's Isothermal phase, Heat is said to be absorbed. Energy of the Carnot Engine in Isothermal phase as per Ideal Gas equation should be: $$E=\frac32nRT$$ Since the amount of Gas($n$) and ...
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Why can Carnot efficiency only be 100% at absolute zero?

So I know that the efficiency of a Carnot engine is given by $1-T_c/T_h$. This tells us that even with an idealised cycle we can never have a 100% efficient heat engine unless $T_c$ is $0$ K or $T_h$ ...
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Light-driven Carnot engine

Based on the definition of the Carnot engine, it is reversible, runs in a cycle, and is frictionless, which would result in the conclusion that the Carnot engine is the most efficient engine. The ...
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How do we use $Δh=v(Δp)$ in pumps assuming $ΔT=0$ while the temperature can increase for the fluid such as in rankine cycle?

In incompressible fluids, for liquids & Constant-temperature processes, as in pumps $(ΔT=0)$ then $Δh=v(Δp)$ . But for a pump in Rankine cycle it will increase the temperature.So, how will we ...
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Will the moisture content in steam turbine power plant decrease the work expansion of the turbine?

In a steam turbine power plant. If the moisture content is increased during the expansion of turbine stages. Will Wturbine decrease because of some of the steam has been converted from gas to water?
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Is $Q=TS$ valid for externally reversible process or internally reversible process?

For $q=tds$ is this equation valid for externally reversible process or internally reversible process? Like for example a heat transfer process in Rankine Cycle is internally reversible but not ...
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How does the heat transfer in carnot cycle occur without a temperature difference between the reservoir and the fluid?

If the temperature of reservoir in carnot cycle (Th) is the same of the fluid's temperature (Th also) then how the heat will transfer . I know that heat transfer from a hotter substance to a lower ...
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Why $W_{\rm net, out} = W_{\rm out} - W_{\rm in}$?

Why when we use thermal efficiency the $\text{net work output} = W_{\text{out}}-W_{\text{in}}$ I asked my friend once he told me is that because we need the useful work but I told him an example in ...
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What puts a limit on lowering $\langle T\rangle$ low avg in heat engines?

I have a simple question which is: We know that the thermal effeciency in heat engines increases when we lower the average temperature at which heat is rejected. But the problem is that there is ...
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How will the compression ratio increase thermal effeciency of otto cycle while Win is higher?

Why the ideal otto cycle thermal effeciency increase with compression ratio although that will increase work input? While the temperature difference in the combustion chamber could be low,the overall ...
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Will increasing or decreasing $\langle T\rangle$ improve thermal efficiency for all power cycles?

The statement: Increasing the average temperature, $\langle T\rangle$, at which heat is supplied to a fluid or decreasing the average temperature at which heat is rejected from a fluid increases the ...
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Why lowering the condenser's temperature is limited?

Why is lowering the condensers pressure limited by a 10 °C difference between the fluid and the sink source in cycles like Rankine 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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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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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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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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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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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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