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Will a Modified Maxwellian Demon Experiment Using Charged Particles Be Able to Recycle Heat?

(If necessary this experiment can be conducted in an environment where gravity is negligible to avoid gravitational effects.) Two adjacent containers are filled with a homogenous gas composed of ...
Jacob Miller's user avatar
7 votes
2 answers
3k views

Do thermodynamic cycles occur only in human-made machines?

Intuitively, it seems like heat engines and refrigerators require a good bit of technology to make a working substance pass through different thermodynamic states and then finally return to the ...
ether's user avatar
  • 325
5 votes
4 answers
797 views

Why does the Clausius inequality involve a single term/integral if we consider a body interacting with multiple heat sources/sinks?

I see that the Clausius inequality was derived for a system interacting with multiple bodies at temperatures $T_{1}, T_{2}, \ldots, T_{n}$ and heat exchanges $\delta Q_{1}, \delta Q_{2}, \ldots, \...
Maximal Ideal's user avatar
0 votes
0 answers
48 views

In a fast moving space ship, can you harvest energy from the radiation background?

In a fast moving space ship (let's say a meaningful portion of c), radiation coming from the front is blue-shifted, while the one coming from behind is red-shifted. Meaning the part of the universe ...
kutschkem's user avatar
  • 745
0 votes
1 answer
38 views

Effect of adiabatic compression of air with cooling water

In the context of a hypothetical method for CAES, I was comparing the following two scenarios: Assume that in the first case air is compressed in an adiabatic process from ambient pressure to ...
Andreas Eisele's user avatar
0 votes
2 answers
74 views

Does temperature difference alone equate to stored energy?

A heat engine uses a temperature difference in a hot side and a cold side to produce work. But when you run a heat engine, with a fixed amount of heat in the hot and cold sides until equilibrium is ...
CPlus's user avatar
  • 1,009
2 votes
2 answers
100 views

Validity of second law of thermodynamics?

Is second law of thermodynamics only valid for isolated systems? What about closed systems and open systems? Since there is exchange of both mass and energy in open systems, wouldn't that violate 2nd ...
aadim sapkota's user avatar
0 votes
0 answers
24 views

Heat gun element to heat a glass furnace?

The general function of a heat gun is to increase the temperature of ambient air to a set temperature. My broken heat gun is rated at 1100 F. I have successfully melted a soda bottle in a campfire and ...
Vogon Poet's user avatar
0 votes
0 answers
75 views

Confusion about finding enthalpy change

I have a confusion about something in the following question. An ideal diesel engine has a compression ratio of 20 and uses air as the working fluid. The state of air at the beginning of the ...
Yigidocan's user avatar
0 votes
2 answers
195 views

What makes a perpetual motion machine of the second kind actually “perpetual”?

As I understand it, a perpetual motion machine does continuous work without additional energy input. If a perpetual motion machine of the second kind exists, it violates the second law of ...
Alex Walczak's user avatar
1 vote
2 answers
29 views

Shape of chamber in thermodynamic machine

Why doesn't the shape of the chamber in a thermodynamic machine/heat engine influence the efficency? Wouldn't a bell / parabola / cone shaped chamber help turn brownian motion into mechanical work of ...
Lorenzo Von Matterhorn's user avatar
1 vote
0 answers
84 views

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 ...
EngineeringMind's user avatar
0 votes
1 answer
80 views

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. ...
Vinayak 's user avatar
0 votes
2 answers
73 views

Analyzing $T$-$S$ diagrams

This is the motivation behind my question; what would the longest line therein translate into on a $p$-$V$ curve? It is evident that the horizontal line is an isothermal process and the vertical line ...
Cognoscenti's user avatar
4 votes
1 answer
228 views

Why are the efficiencies of real heat pumps so far from the theoretical limits?

The theoretical coefficient of performance of a heat pump for warming is $\frac{T_h}{\Delta T}$. Take an example of an outdoor temperature of -15C and an indoor of 20C, one then has COP = 293/35 = 8....
eshaya's user avatar
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0 answers
28 views

Why is a heat sink required? [duplicate]

In 'Thermodynamics' , the section under "heat engines" mentions, that, it is practically impossible to create an engine which can operate with just a heat source and no heat sink present. ...
GodP7's user avatar
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2 votes
0 answers
82 views

Question about the equivalence between Kelvin-Planck and Clausius

When we try to prove that if Clausius statement violated then KP is also violated we assume that that cold source gives the same amount of heat as it receives. My question is: How is this proof ...
randomdude's user avatar
0 votes
0 answers
16 views

Efficiency questions in a closed loop expander

So let's say I have a condenser, and both the inlet and outlet are connected to a pressure vessel that has hot gas fluid. Let's say there is a pneumatic pump creating a load on the connection to the ...
sergbot's user avatar
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1 answer
48 views

In this Stirling Engine process, how do we know that the fluid is heating up?

Since the volume of fluid in contact with the cold source and hot source is the same, how do we know the fluid is heating up instead of cooling down?
Maxine's user avatar
  • 23
7 votes
4 answers
3k views

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 ...
joshuaronis's user avatar
  • 3,075
0 votes
2 answers
52 views

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 ...
Antoin Roquentin's user avatar
0 votes
0 answers
32 views

How would a heat engine with 3 bodies work?

Say we have 3 equal bodies in contact, and there is a heat engine that absorbs and emits heat to these 3 bodies and it does work to an external medium. How would that work? I imagine that it would get ...
Ulshy's user avatar
  • 69
4 votes
2 answers
2k views

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 ...
Manav M Nair's user avatar
0 votes
1 answer
42 views

Approaching ideal efficiency of a thermal machine

Say we have a standard thermal machine which operates in cycles. It absorbs energy in form of heat from a hot source, does some work and then transmits the remaining energy to the cold sink also in ...
Lagrangiano's user avatar
  • 1,631
0 votes
1 answer
203 views

Efficiency of a cyclic processes [closed]

Is there a specific formula for solving the efficiency of a cyclic process in pV diagram? I have this diagram of a diatomic ideal gas cyclic process, where ${p} = 4{p_0}$ and ${V} = 4{V_0}$ The work ...
mama b's user avatar
  • 1
0 votes
2 answers
166 views

Calculation of specific heat experimentally and mechanical equivalent of heat

After reading some books and some google searches and reading some answers on stack exchange physics what I have understand is (correct me if I am wrong) to calculate heat supplied we need change in ...
Rahul Einstien's user avatar
0 votes
1 answer
27 views

Efficiency of a refrigeration machine with inverted sign

I'm trying to calculate the efficiency of an ideal refrigeration machine ($η$) and I keep getting the right result with the wrong sign. My reasoning is as follows (I've attached a sketch for more ...
Lagrangiano's user avatar
  • 1,631
0 votes
3 answers
135 views

Why does adiabatic expansion occur in the Carnot cycle?

Several people have asked this question before and I haven't found any of the explanations even remotely satisfying. To begin, Let's imagine our system consists of an ideal gas enclosed in a cylinder ...
Zachary Candelaria's user avatar
0 votes
1 answer
46 views

Efficiency of a Rankine cycle [closed]

So the efficiency of a Rankine cycle is given by the formula $$e=1-\frac{Q_{c}}{Q_{h}}=1-\frac{H_{4}-H_{1}}{H_{3}-H_{2}} \approx 1-\frac{H_{4}-H_{1}}{H_{3}-H_{1}}$$ I understand that the change in ...
lynx_s's user avatar
  • 9
1 vote
1 answer
233 views

Humphrey vs Brayton cycle efficiency

In practical engineering we are limited in the upper temperature of thermodynamic cycle due to the material properties. So, after the max temperature is fixed, we want to make our cycle as close as ...
Demid Zharenov's user avatar
1 vote
0 answers
28 views

Is it possible for an absorption refrigerator to pump heat to a reservoir that is at a higher temperature than the heat source used to run it?

Judging by the wiki page I get the feeling that this type of heat pump would not function if it's radiator were hotter than the heat source, but I can't quite put into words why and I feel like there ...
MLG Samantha's user avatar
0 votes
1 answer
106 views

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 ,...
Doctor Pinocchio's user avatar
0 votes
2 answers
63 views

Apparently Spurious Argumentation in Justification of Clausius Inequality

In section 7-1 of Cengel and Boles text, "Thermodynamics - An Engineering Approach", the authors give a demonstration of the validity of the Clausius Inequality. In their justification, the ...
Zachary Candelaria's user avatar
0 votes
1 answer
95 views

Would introducing water into a piston increase or decrease pressure?

Suppose you were to introduce a small amount of liquid water into the cylinder of an IC engine just after combustion. The timing and amount of water would be such that the water was entirely vaporized ...
David Gudeman's user avatar
5 votes
4 answers
3k views

How can an airconditioning machine exist?

I work in an office where the airconditioning is not working, so I brought a small mobile airconditioning device: it's a small machine, emitting cooled air. It looks like this: However, according to ...
Dominique's user avatar
  • 185
0 votes
2 answers
106 views

A violation of the Maximum Work Theorem?

Consider the PV diagram I've drawn at the end of this post. Consider the processes drawn thereon: (1-2-3) is an isobaric step followed by an isochoric step, while (1-3) is an adiabatic expansion (I ...
EE18's user avatar
  • 1,095
-1 votes
2 answers
274 views

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 ...
Ziaul Hasan Hamim's user avatar
-1 votes
1 answer
769 views

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
xxx's user avatar
  • 41
0 votes
2 answers
113 views

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 ...
Shridp's user avatar
  • 128
2 votes
4 answers
236 views

Why is the number of thermodynamic systems (that do not do work) in this scenario two?

The hardest thing for me about studying thermodynamics, is connecting the formal theory with actual problem instances. Here is an example: In Callen’s Thermodynamics and an Introduction to ...
Lior's user avatar
  • 3,369
1 vote
5 answers
277 views

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. ...
Ken Horne's user avatar
1 vote
4 answers
1k views

Why can't a heat engine have 100% efficiency?

Using the idea of isotherms and adiabats, I came up with the following argument to convince myself. First imagine the working gas within the system being heated along an isochore (hence all heat ...
Y G's user avatar
  • 57
1 vote
4 answers
116 views

Distinction between "types of heat" in thermal efficiency

The definition of thermal efficiency I see in several sources is "total work" divided by "heat input". Wikipedia, for example, says: "For a heat engine, thermal efficiency is ...
thedude's user avatar
  • 628
3 votes
2 answers
138 views

Should I put my freezer in the middle of the living room? [duplicate]

There is a freezer in my kitchen. It has frozen fish fingers and spinach and potato waffles and leftovers. The food stays below freezing temperature using the principle of latent heat. The freezer ...
Daron's user avatar
  • 309
2 votes
3 answers
602 views

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. ...
Mr. Wayne's user avatar
  • 353
0 votes
1 answer
62 views

Thermoacoustic mechanism for a thermoacoustic engine

How exactly does a thermoacoustic engine work? (I don't mean the engineering part) I understand the part on the Brayton cycle occurring and all, but how might we measure the numerical efficiency for ...
Stack Man's user avatar
0 votes
1 answer
148 views

How does an internal combustion engine reduce the heat produced by burning fuel?

If I understand correctly, any heat produced by an internal combustion engine can be considered "waste heat"; energy from the fuel that did not get converted to mechanical energy. But if you ...
Lorry Laurence mcLarry's user avatar
0 votes
1 answer
77 views

The suction and thrust of an aircraft engine

Does only the air sucked in (not the air that is ejected at the back of the engine) by an airliner engine (turbofan engine) causes a thrust forward or in other words pull the engine forward? and why ? ...
Sebastyen Laroche's user avatar
6 votes
1 answer
1k views

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 (...
JustCurious's user avatar
1 vote
2 answers
157 views

Vapor Compression Refrigeration Cycle

My question here is, why do we need point 2 to be on the saturated liquid line, i.e. why do we need a saturated liquid for the throttling process? Why can we not use it in the liquid region or ...
nishesh singh's user avatar

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