Thermodynamics cycle with liquid and gas

Click For Summary

Discussion Overview

The discussion revolves around the feasibility of a thermodynamic cycle involving both liquid and gas phases, specifically addressing the transitions between these phases and the implications for energy conservation and thermodynamic laws. Participants explore the mechanics of the cycle, particularly focusing on the conditions under which a gas can become a liquid and the energy dynamics involved.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions the possibility of a gas transitioning to a liquid at step 3 of the cycle, suggesting that the gas cannot become a liquid under certain conditions.
  • Another participant proposes that heating from the atmosphere at step 2 could provide the necessary energy for the process, but raises concerns about the implications for the second law of thermodynamics if the system only recovers energy from one source.
  • A participant suggests that a heat sink is necessary to cool the mixture to achieve step 3, referencing the concept of a Stirling engine.
  • One participant expresses uncertainty about the expansion of gases and their temperatures, questioning why a gas (G2) does not liquefy despite being under pressure from another gas (G1) during the expansion process.
  • Another participant discusses the conservation of energy balance, asserting that if the gas returns to its original state, the energy dynamics may not hold, particularly if heat transfer or net work is involved.
  • A later reply seeks clarification on the energy recovery process during the phase transition, indicating a lack of understanding of the underlying thermodynamic principles.

Areas of Agreement / Disagreement

Participants express differing views on the mechanics of the thermodynamic cycle, particularly regarding the phase transitions and energy conservation. There is no consensus on the feasibility of the proposed cycle or the conditions necessary for the gas to become a liquid.

Contextual Notes

Participants reference the second law of thermodynamics and the need for a heat sink, indicating potential limitations in their understanding of thermodynamic processes. The discussion includes assumptions about the system's isolation and the role of external heating.

Who May Find This Useful

This discussion may be of interest to those studying thermodynamics, particularly in understanding phase transitions, energy conservation, and the implications of thermodynamic laws in practical applications.

Gh778
Messages
419
Reaction score
0
I'm trying to find why this thermodynamics cycle is not possible but I don't find. The only problem for me is at step 3, the gas can't become a liquid but why ?
 

Attachments

  • g1g2b.png
    g1g2b.png
    14.9 KB · Views: 535
Science news on Phys.org
nobody for help me ?
 
What about the heating of the cylinder at step 2? Maybe that's where the Energy comes from. If it does than you will not have any problem.
didn't you say that it's an insulated system? If it is, how does the atmosphere heats it? If it's not, energy can move from the system to the atmosphere.
 
The system is isolated except heating from atmosphere. The heating from atmosphere give energy to gas and liquid at step 2. But like that, the system recover energy from only one source of heating, this break the 2° law of thermodynamics and it's not possible.

My questions is: Is it possible to have a liquid from 2 gas with different temperature for the transformation in liquid (butane and propane for example) ? Is it possible to step 3 to exist ?
 
I'm not sure because the expansion of gas reduce temperature of 2 gas, if this temperature is below the temperature of liquefaction of gas G2, why this gas don't become a liquid because it has always a pressure from G1 gas ? The expansion of 2 gas can continue in the time G2 become a liquid, because G2 will give energy to G1 during the time of liquefaction. For example, with G1=nitrogen and G2=butane.
 
Last edited:
If the gas cooled and compressed itself to where it started, the conservation of energy balance wouldn't work out. Compression and expansion are reversible only if there is no heat transfer or net work out.

I suggest getting a thermodynamics textbook and start learning how these processes work rather than just guessing. Or at least read the wiki page on this.
 
If the gas cooled and compressed itself to where it started, the conservation of energy balance wouldn't work out.
Could you explain a little more, I don't understand ?

For me: if the valve give works at step 3, G1 and G2 lost temperature, when G2 start to become a liquid it give energy at G1 gas, this energy can be recover from valve. When G2 is liquid: stop to recover energy form valve. But the reality is how ?
 

Similar threads

Graduate Can Hamson-Linde cycle liquidize N2?
  • · Replies 7 ·
Replies
7
Views
3K
Undergrad So what are the definitions of gas, liquid, solid?
  • · Replies 20 ·
Replies
20
Views
2K
Undergrad What thermal cycle would describe the action of a candle carousel?
  • · Replies 4 ·
Replies
4
Views
1K
Undergrad Do refrigerants passing through a venturi act like steam?
  • · Replies 8 ·
Replies
8
Views
3K
Undergrad How to calculate the mass of gas in a tank?
  • · Replies 109 ·
4
Replies
109
Views
9K
Undergrad Paradox: Thermodynamic equilibrium does not exist in gravitational fields
  • · Replies 135 ·
5
Replies
135
Views
9K
Graduate Vacuum Flask Thermodynamic Equation
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Adiabatic cooling in this process involving liquid ammonia
  • · Replies 5 ·
Replies
5
Views
3K
Undergrad Resulting temperature of mixed liquids
  • · Replies 5 ·
Replies
5
Views
2K
Undergrad Thermodynamics and ideal gas law concepts
  • · Replies 14 ·
Replies
14
Views
2K