Can cold air become water in a vacuum cylinder?

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Discussion Overview

The discussion revolves around whether cold air can become water in a vacuum cylinder, exploring the conditions under which water vapor can condense or air can be liquefied. The conversation includes considerations of temperature, pressure, and phase diagrams, with a focus on the implications of operating in a vacuum.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants clarify that the question may refer to condensing water vapor from the air or liquefying the air itself.
  • It is proposed that if the temperature is low enough, it is possible for cold air (or a mixture of cold air and water) to become water.
  • Participants note that reducing pressure in a vacuum lowers the boiling point of water, which could affect the phase changes involved.
  • A participant introduces the concept of the phase diagram for water, explaining that water can exist in solid, vapor, and liquid states depending on temperature and pressure, with a specific mention of the triple point.
  • There is a mention that at low pressures, water cannot exist as a liquid and will transition directly from vapor to solid (sublimation).
  • Some participants express confusion about the implications of a vacuum on the process of condensation or liquefaction.

Areas of Agreement / Disagreement

Participants generally agree on the need to consider temperature and pressure in the context of the phase diagram, but there is no consensus on how a vacuum specifically impacts the ability of cold air to become water.

Contextual Notes

The discussion highlights the complexity of phase changes and the specific conditions required for water to exist in different states, emphasizing the role of temperature and pressure without resolving the implications of operating in a vacuum.

JII
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can cold air become water in a vacuum cylinder?
 
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Welcome to PF!
JII said:
can cold air become water in a vacuum cylinder?
That's a confusing question: water isn't air. So either you mean condensing water vapor that is in the air or liquefying the air. Either can be done if cold enough, but trying to do it in a vacuum works against you.
 
russ_watters said:
Welcome to PF!

That's a confusing question: water isn't air. So either you mean condensing water vapor that is in the air or liquefying the air. Either can be done if cold enough, but trying to do it in a vacuum works against you.
Yes, water vapor
 
JII said:
can cold air become water in a vacuum cylinder?
If you apply a cold enough temperature, then yes it is possible.
And...
:welcome:
 
JII said:
Yes, water vapor
Why would the vacuum work against me?
 
JII said:
Why would the vacuum work against me?
Check out the phase diagram for water or a steam table; As you reduce the pressure, the boiling point goes down.
 
russ_watters said:
Check out the phase diagram for water or a steam table; As you reduce the pressure, the boiling point goes down.
Okay
 
JII said:
can cold air become water in a vacuum cylinder?
Let me re-state "cold air" as "a mixture of cold air and water". Is that OK?
The answer to your question will depend upon the Temperature and the value of the pressure in your "vacuum cylinder". If you look at the Phase Diagram in this link, it shows how the phases of water depend on the pressure / temperature combination. There is a "triple Point" for water (around 0°C) at which water can exist as solid, vapour and liquid and move from one to another. The state of the water, as you leave that point in various directions, is shown on the diagram. One simple fact emerges and that is that water can't exist as liquid towards the bottom left corner of the diagram, for any finite value of low pressure, there is a temperature at which water will pass from [edit] vapour to sold and back, without going through a liquid phase (called Sublimation).
The presence of Air, doesn't make any significant difference to the situation.
 
Last edited:
sophiecentaur said:
Let me re-state "cold air" as "a mixture of cold air and water". Is that OK?
The answer to your question will depend upon the Temperature and the value of the pressure in your "vacuum cylinder". If you look at the Phase Diagram in this link, it shows how the phases of water depend on the pressure / temperature combination. There is a "triple Point" for water (around 0°C) at which water can exist as solid, vapour and liquid and move from one to another. The state of the water, as you leave that point in various directions, is shown on the diagram. One simple fact emerges and that is that water can't exist as liquid towards the bottom left corner of the diagram, for any finite value of low pressure, there is a temperature at which water will pass from [edit] vapour to sold and back, without going through a liquid phase (called Sublimation).
The presence of Air, doesn't make any significant difference to the situation.
Thanks :)
 

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