Air pressure dependent water evaporation

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Discussion Overview

The discussion centers on how air pressure affects the evaporation speed of water, exploring the relationship between total air pressure and the partial pressure of water vapor. Participants consider various air pressure levels and their implications for evaporation rates.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions how evaporation speed changes with varying air pressures, suggesting a range from 1.000Pa to 10.000.000Pa.
  • Another participant asserts that evaporation speed does not change with total air pressure, emphasizing that it is dependent on the partial pressure of water vapor above the liquid.
  • A later reply introduces the idea that if air pressure is lower than the water's vapor pressure, boiling occurs, which significantly increases evaporation speed, although no specific values are provided.
  • Another participant challenges the previous assertion, suggesting that the claim about evaporation speed remaining constant is surprising and incorrect, mentioning the "Poynting correction" as a relevant concept.
  • A participant inquires whether any liquid exists that would change evaporation speed as a function of air pressure.

Areas of Agreement / Disagreement

Participants express disagreement regarding the effect of air pressure on evaporation speed, with some asserting that it remains constant while others challenge this view and introduce additional concepts.

Contextual Notes

Participants reference the importance of distinguishing between total air pressure and partial pressure of water vapor, indicating that assumptions about these definitions may influence their arguments.

lesy1
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Imagine a water basin, surrounded by air. How does evaporation speed of water change if the air pressure of surrounding air is 1.000Pa, 10.000Pa, 100.000Pa, 1.000.000Pa, 10.000.000Pa. What is an order of magnite of the evaporation speed change. Where can I read more about that?
Regards.
 
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The surprising answer is that it doesn't change. The evaporation speed is dependent on the partial pressure of the water vapor above it, not the total pressure of the air.

The exception to this is if the air pressure is lower than the water's vapor pressure. Then the water will boil, which significantly increases its evaporation speed (I don't know an exact number though).
 
Does there exist any liquid which would change the evaporation speed as a function of air pressure?
 
cjl said:
The surprising and incorrect answer is that it doesn't change. (snip)

You are looking for the "Poynting correction."
 

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