Thermodynamic properties of a liquid-gas mixture

In summary, the conversation discusses calculating thermodynamic properties of a 70% steam and 30% air mixture at 90 degrees Celsius and 10 MPa. The boiling point of water at 10 MPa is 311°C. The speaker mentions a helpful website and asks for clarification on the mixture's composition and reference states for determining entropy and enthalpy. They also discuss the equilibrium vapor pressure of water at 90°C and the resulting mass fractions of air and water in the gas phase. Finally, they question whether there will be any water vapor at this pressure and temperature.
  • #1
Rafe Zayed
6
0
How can I calculate thermodynamic property like entropy and enthalpy of 70% steam and 30% air mixture ?( at about 90 degree Celsius and 10 MPa)
 
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  • #2
The boiling point of water at 10 Mpa is 311°C
 
  • #3
Rafe Zayed said:
How can I calculate thermodynamic property like entropy and enthalpy of 70% steam and 30% air mixture ?( at about 90 degree Celsius and 10 MPa)
Welcome to the PF.

This is a pretty useful website that you may find helpful in your learning: http://www.thermopedia.com/content/1150/

:smile:
 
  • #4
Do you mean 30 mole %? Are you willing to assume that the mixture is an ideal gas mixture? What are the reference states of the air and water relative to which you desire to determine the entropy and enthalpy?
 
  • #5
Chestermiller said:
Do you mean 30 mole %? Are you willing to assume that the mixture is an ideal gas mixture? What are the reference states of the air and water relative to which you desire to determine the entropy and enthalpy?
No I mean 30% by mass fraction.
And at this high pressure ,water will be liquid. So I am not sure whether I can treat them as gas mixture or liquid gas mixture.
Any suitable reference point will do.Basically I want to find the property of a liquid -gas mixture
 
  • #6
What is the equilibrium vapor pressure of water vapor at 90 C?
 
  • #7
Chestermiller said:
What is the equilibrium vapor pressure of water vapor at 90 C?
According to internet I found it to be around 70000 Pa
 
  • #8
Rafe Zayed said:
According to internet I found it to be around 70000 Pa
Good. So that's about 0.07 MPa. If you're willing to tentatively approximate the gas phase as an ideal gas mixture, then that would be the partial pressure of water vapor in the gas phase. And at a total pressure of 10 MPa, what would be the mole fraction of water vapor in the gas phase? From these results, what would be the mass fractions of air and water in the gas phase? On the basis of 1 kg of water and air, what would be the mass of air? What would be the mass of water vapor in the gas phase? How much water would that leave for the liquid phase?
 
  • #9
Chestermiller said:
Good. So that's about 0.07 MPa. If you're willing to tentatively approximate the gas phase as an ideal gas mixture, then that would be the partial pressure of water vapor in the gas phase. And at a total pressure of 10 MPa, what would be the mole fraction of water vapor in the gas phase? From these results, what would be the mass fractions of air and water in the gas phase? On the basis of 1 kg of water and air, what would be the mass of air? What would be the mass of water vapor in the gas phase? How much water would that leave for the liquid phase?
Sorry ,I didn't get that.At this pressure will there be any water vapour?Won't all the water vapour turn into liquid?
 
  • #10
Rafe Zayed said:
Sorry ,I didn't get that.At this pressure will there be any water vapour?Won't all the water vapour turn into liquid?
Not all, but most.
 

1. What are the thermodynamic properties of a liquid-gas mixture?

The thermodynamic properties of a liquid-gas mixture refer to the physical characteristics of a substance when it exists in both liquid and gas phases. These properties include temperature, pressure, volume, and energy, and they can be used to study the behavior and transformations of the mixture.

2. How do temperature and pressure affect the properties of a liquid-gas mixture?

Temperature and pressure have a direct impact on the thermodynamic properties of a liquid-gas mixture. As temperature increases, the molecules in the mixture gain kinetic energy and move faster, causing the substance to transition from a liquid to a gas. Pressure also affects the properties by compressing the molecules, which can lead to changes in volume and density.

3. What is the difference between partial pressure and total pressure in a liquid-gas mixture?

Partial pressure refers to the pressure exerted by a specific gas in a mixture, while total pressure is the combined pressure of all gases in the mixture. In a liquid-gas mixture, partial pressure can be used to determine the amount of each gas present, while total pressure reflects the overall conditions of the mixture.

4. How do changes in energy affect the properties of a liquid-gas mixture?

Changes in energy, such as heat transfer, can lead to changes in the thermodynamic properties of a liquid-gas mixture. Adding heat can cause the substance to vaporize, while removing heat can cause it to condense. This can alter the temperature, pressure, and volume of the mixture.

5. What are some practical applications of studying the thermodynamic properties of a liquid-gas mixture?

Understanding the thermodynamic properties of a liquid-gas mixture is crucial in many industries, such as chemical engineering, environmental science, and energy production. This knowledge can be used to design and optimize processes, such as distillation and refrigeration, and to predict and prevent potential hazards, such as explosions or leaks.

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