Questions tagged [carnot-cycle]
The carnot-cycle tag has no usage guidance.
131
questions
0
votes
1answer
55 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 ...
-3
votes
2answers
56 views
Efficiency of Carnot engine [duplicate]
Why is the efficiency of Carnot engine regarded as the maximum efficiency possible for a heat engine?
1
vote
2answers
111 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:
...
3
votes
2answers
99 views
Why is the Peltier / Seebeck Effect's efficiency so low in practical devices?
Usually solid state devices are able to attain excellent efficiency. However, currently existing Peltier coolers and Seebeck generators have horrible efficiency -- far worse than Carnot, and also far ...
0
votes
2answers
80 views
Thermodynamics problems with a cycle (insufficient data?)
I am having some troubles in solving the following problem a professor gave us, and in my opinion I think that either there are insufficient data or the solutions are infinite.
We have a perfect gas,...
1
vote
2answers
59 views
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 (...
0
votes
1answer
56 views
Clausius's Carnot Cycle Equation Derivation
In his paper clausius describes a Carnot cycle and he continue arguing like below:
In order to make an analytical application of the method...we will assume that all the changes which the gas ...
0
votes
2answers
106 views
Calculating efficiency of a Engine
Given are four points in a PV-diagram: $(V_1, 3/2P_1)$ is the leftmost point, $(V_2,3/2P_1)$ is the rightmost point, $(\frac{V_1+V_2}{2},P_1)$ is the lowest point and $(\frac{V_1+V_2}{2},2P_1)$ is the ...
4
votes
3answers
226 views
Why is there Net Work Done on a Pressure/Volume Cycle?
The area enclosed by the rectangle is said to be the Net Work Done. My question is why would there be any net workdone if it returns to its initial position (W).
Shouldn't it act like a force-...
0
votes
1answer
62 views
Can you calculate the supplied heat given a p(V) - Diagram of a isobar process?
You are given an p(V) - Diagram like this:
Source: How to calculate the efficiency from a $p$-$v$ diagram?
There you see two isothermal processes and two isochor processes.
For every given ...
4
votes
2answers
390 views
Why does there need to be an isothermal compression in a Carnot cycle?
This is the part that allows the Carnot engine to not violate the 2nd law of thermodynamics, but, hypothetically, why can't we just adiabatically compress the working substance to get it back to State ...
1
vote
1answer
198 views
Why is there a cold reservoir in a Carnot engine?
I'm trying to wrap my head around the idea behind a Carnot engine.
The main question I'm trying to figure out is how a Carnot engine actually works in producing work.
I'll provide a picture for ...
0
votes
1answer
40 views
Deriving the second law of thermodynamics from an irreversible carnot process
I have studied the ideal carnot cycle extensively where we assume that
$$\Delta S_{\mathrm{total}}=\sum_i \frac{Q_i}{T_i} =0$$
Now I was wondering whether it is possible to derive basic properties ...
0
votes
1answer
57 views
Limitations of converting pressure into kinetic energy
Bernoulli's principle states that an increase in the kinetic energy of a fluid occurs simultaneously with a decrease in pressure for isentropic processes. What then limits us from converting all of ...
0
votes
2answers
346 views
How do I prove that the Carnot cycle is the most efficient graphically? [closed]
I have to prove that the Carnot cycle is the most efficient by comparing it with a arbitrary cycle working within the temperature range of $T_L$ to $T_H$ in a ST-diagram. How do I do this?
1
vote
1answer
50 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
votes
2answers
144 views
How is the work done by Carnot Engine obtained or converted to usable form?
I read about the Carnot Cycle and Carnot engine where it was said that the work done by this engine is equal to the area enclosed in the PV diagram. I understood the proof and everything but I am not ...
-1
votes
1answer
33 views
Efficiency of a Carnot machine, in which, some of its extreme points are in the region of liquid transition to steam
I need to calculate the efficiency of a Carnot machine, in which, some of its extreme points are in the region of liquid transition to steam with the works, differences of energy and heats of each ...
-1
votes
1answer
96 views
Carnot's Engine Proof flawed?
https://www.youtube.com/watch?v=LUoUb4hGMH8
I was looking at the reason as to why a Carnot Engine and watched this video on KhanAcademy. He used a very clever method of proving this by using the ...
1
vote
2answers
64 views
Thermodynamic cycles
Consider a system that takes excess air (assume it to be an ideal gas, $Cp = \frac{7}{2} R$) from a power plant stack at $370 \rm K$ (typo in figure) and $2$ bar and compresses it to 20 bar ...
6
votes
5answers
2k views
Does chaining Carnot heat engines make them more efficient?
Since the efficiency of a Carnot cycle depends on the difference between the hot and cold sides of the engine, could you put multiple heat engines in a series to maximize overall efficiency? A $3000 \,...
5
votes
2answers
794 views
Total Reversibility of Carnot Cycle
I was reading about Carnot cycle in "Thermodynamics by Cengel & Boles", now it is stated that Carnot cycle is a totally reversible cycle, i.e it is an internally as well as externally reversible ...
1
vote
2answers
423 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 ...
0
votes
1answer
228 views
Actual sequence of refrigeration cycle
Whenever i have studied refrigeration cycle on books, i have found that the diagrams are always explained starting from the compressor*, then condenser then throttle and finally evaporator. I find it ...
1
vote
1answer
395 views
Validity of Carnot's theorem when operating between finite reservoirs
Carnot’s theorem tells us that "the most efficient heat engines operating between 2 reservoirs have the same efficiency as a Carnot engine".
This theorem assumes that the engines are operating ...
1
vote
1answer
1k views
Reversible and irreversible cycles: Changes in entropy of the system and the surrounding
Entropy is a state function.
Is it true that at the end of a cyclic process, the change in entropy of the of the system and that of its surrounding are both separately zero irrespective of whether ...
0
votes
3answers
141 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 ...
0
votes
2answers
247 views
Heat transfer in the isothermal expansion in the Carnot cycle
Problem
In the Carnot cycle there are two adiabatic and two isothermal processes. This question focuses on the isothermal expansion.
In the isothermal expansion books often writes that the system is ...
1
vote
1answer
296 views
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 ...
2
votes
1answer
370 views
Carnot Engine - Maximum Efficiency Proof?
As an introductory physics student (independently studying before my return to official classes this summer), I am given a "proof" that the Carnot engine has the maximum efficiency possible by way of ...
0
votes
1answer
243 views
How Much Heat Is Absorbed/Rejected By The Heat Engine?
If a heat engine undergoes a reversible cycle consisting of two isobaric processes and two adiabatic processes, what methodology is used to determine how much heat is absorbed or rejected by the heat ...
1
vote
1answer
419 views
How do we know that entropy is a state function given by $\delta Q_{\mathrm{rev}}/T$ for any arbitrary (not just reversible process)?
In this video, the professor goes through a "derivation" for entropy using the Carnot cycle, in which he establishes that entropy is a state function for that process.
However, he then continues the ...
1
vote
2answers
782 views
Prove carnot engine is most efficient
According to Carnot's theorem, Carnot engine is the most efficient engine. I wanted to know its proof. I looked up and I found a proof on Khan Academy in which he used a reverse carnot engine to prove ...
1
vote
2answers
768 views
Why is the entropy of a Carnot engine always constant?
I am 99% sure that I am wrong here, but here is my reasoning.
The efficiency of a Carnot engine can be written as:
$$
\eta_{carnot} = 1 - \frac{T_f}{T_i}
$$
But since Effency's definition says $\...
1
vote
0answers
258 views
Why can't a Carnot engine heat sink be at absolute zero? [duplicate]
We know that for a Carnot engine the efficiency is given by $1-(T_2/T_1)$, but why can't a real engine have $T_2=0\,{\rm K}$?
I know that the efficiency cannot be $1$, but why can't we make the heat ...
0
votes
2answers
400 views
Is the efficiency of a reversible heat engine independent of the processes involved?
Does the following question conflict that fact that efficiency of a reversible engine is independent of processes involved?
0
votes
2answers
226 views
What makes a process reversible?
I just want someone to verify what I think.
I originally thought that for a reversible process to occur, no irreversibilities like friction can occur. Nevertheless, if we consider the Carnot ...
1
vote
3answers
247 views
Why doesn't the heat in the two isochoric processes count towards efficiency calculation in Stirling cycle?
I'm trying to understand Stirling Cycle that consists of two isochoric processes and two isothermal processes. The heat transfer are given as
$$Q_1 = \nu RT_1 \mathrm{ln} \frac{V_1}{V_2}$$
$$Q_2 = ...
0
votes
1answer
31 views
Carnot cycle restoration of original system state
In the Carnot cycle the original state is restored so there is no overall change in entropy. Why is it not possible to accomplish this simply with two reversible isothermal steps, the first an ...
2
votes
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?
1
vote
0answers
81 views
Is there only one Carnot cycle for every thermodynamic system?
So, Carnot engine is THE reversible engine operating on two reservoirs. No other engine can beat its efficiency on two reservoirs (eg. Otto cycle is not Carnot as it requires infinite number of ...
4
votes
0answers
116 views
Are there actual technical realizations of the Carnot cycle?
The Carnot cycle is composed of four steps: isothermal expansion, adiabatic expansion, isothermal compression and adiabatic compression.
In the case of combustion engines, we have the idealized Otto ...
0
votes
1answer
87 views
Is my interpretation of how a Carnot Cycle works correct?
I'm trying to understand how the Carnot cycle works in my learning of it. Here's what I so far believe is what is happening:
(A $\to$ B) A cylinder of gas is connected to a frictionless piston, and ...
0
votes
1answer
872 views
Does Piston moves faster when we accelerate the car?
I am learning about car basics. I found that engine is nothing but a system where heat energy is converted into up/down motion of the piston in the cylinder. Finally, this up/down motion is converted ...
0
votes
2answers
161 views
About the 2nd Carnot Corollary
I have a question about the 2nd Carnot Corollary.
According to Moran, Fundamentals of Engineering Thermodynamics, the 2nd Carnot Corollary stated that "all reversible power cycles operating between ...
0
votes
1answer
108 views
Does a Carnot-efficient heat engine recover all work that was initially done?
There are two adiabatic containers filled with an ideal gas. In container A work is done which eventually turns completely into heat, leading to a temperature difference between container A and ...
0
votes
0answers
126 views
Cascade Carnot cycle
In a Carnot cycle about 50% of the energy is converted in work whereas the other is dissipated in heat to the heat sources.
Is it possible to reuse the heat in another cycle to reconvert 50% of it ...
1
vote
0answers
199 views
Confusion about Clausius inequality
I am trying to learn the derivation of Clausius inequality in the following manner. Consider the following diagram
"Reversible cyclic device" is working in Carnot's cycle. The combined system gets ...
0
votes
1answer
92 views
Reverse the combustion engine
All you know what a combustion engine is doing: Transform chemical energy into kinetic energy.
What about the opposite? I know when I park a car at a slope and lose the breaks it will drive ...
0
votes
1answer
114 views
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 ...
