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.
Questions tagged [carnot-cycle]
252 questions
40
votes
4 answers
Why is the efficiency of human cells less than the efficiency of an Otto engine?
I always used to think (I don’t know why!) that the efficiency of human (and animal and plant) cells should be equal to or near the efficiency of a Carnot engine or at least should be the highest efficiency among all practical engines. But I…
lucas
- 3,199
33
votes
5 answers
Efficiency of Stirling engine and Carnot's theorem
I want to calculate the efficiency of this Stirling cycle for an ideal gas $pV = nRT$
The mechanical work is
$$
\Delta W_{12} = - \int_{V_1}^{V_2} p(V) \mathrm{d}V = -nRT_2 \ln \frac{V_2}{V_1}\\
\Delta W_{23} = \Delta W_{41} = 0\\
\Delta W_{34} =…
frankundfrei
- 433
23
votes
5 answers
Can I take heat from the air and convert it to electricity?
Its a summer day and the air in my house has been heated up. I could switch on my air conditioning, but then I'd be using energy from the grid in order to reduce the amount of energy in my house.
What I'd much rather do is capture the heat energy…
billpg
- 856
17
votes
3 answers
Why is the Carnot engine the most efficient?
It seems that the only condition used in proving that the Carnot engine is the most efficient is that it is reversible. More specifically, the Carnot engine can be run in reverse as a refrigerator. Furthermore, it is asserted that all reversible…
curiousgeorge
- 865
10
votes
10 answers
Why can't we make Carnot heat engine in real life?
Question is obvious: Why can't we make Carnot heat engine in real life?
I read Wikipedia and Fundamentals of Physics (Halliday) but I haven't found anything on my question. There are explanations about formulas and how it works but no obvious answer…
titansarus
- 221
8
votes
3 answers
The Carnot engine and entropy?
The Clausius statement of the second law of thermodynamics is as given below:
"Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time."
Why is this statement true and exactly…
user106570
7
votes
4 answers
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 between two heat reservoirs, with an efficiency of 1…
joshuaronis
- 3,145
7
votes
3 answers
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 in some places.
If they could be equally…
Daniel Mahler
- 3,560
6
votes
1 answer
Adiabatic proccess and Carnot cycle in a photon gas
I am making a comparation between the photon gas and the ideal classic gas for my Thermodynamics class. The photon gas is defined by the equations:
$$U=aVT^4 $$
$$P=\dfrac{1}{3}aT^4$$
I found this document:…
Victor Buendía
- 1,208
6
votes
1 answer
Does isothermal expansion not beat the efficiency of Carnot Heat Engine?
Ques:
If I just take the 1st step of a Carnot Heat Engine (CHE) than it turns out to be more efficient than the CHE itself.
Explanation:
The 1st step of a CHE is the pure isothermal expansion of (ideal) gas where all the heat($Q$) taken from the…
JustCurious
- 95
6
votes
4 answers
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 the incident light into its spectrum and
use…
tobalt
- 2,423
6
votes
4 answers
Why can Carnot efficiency only be 100% at absolute zero?
I know that the efficiency of a Carnot engine is given by $1-T_c/T_h$. This tells us that even with an idealized cycle, we can never have a 100% efficient heat engine unless $T_c$ is $0\,\text{K}$ or $T_h\to\infty$. I'm having a bit of trouble…
dbp1023
- 61
6
votes
2 answers
Is Carnot cycle the only "most efficient" cycle?
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 provide mathematical explanation for why that is or…
user249968
6
votes
1 answer
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:
First, we approach a hot source and the gas expands…
Álvaro Franz
- 359
6
votes
5 answers
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 $3000 \, \text{K} \to 2000 \, \text{K}$ engine connected…
jerpyatdm
- 63