Frost preferentially forms on non-vertical car windows?

In summary: Horizontal vs vertical boundary layer effect may play a role - the horizontal boundary layer is closer to the surface of the window and is therefore warmer and can hold more water vapor, leading to frost. Gravity driven vertical diffusion of water vapor may play a role as well - as the vapor rises, it is pulled along the surface of the object and may freeze.
  • #1
Frabjous
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Going out to my car this morning, I noticed that frost preferentially formed on non-vertical windows. I can come up with three explanations

1) non-vertical windows are dirtier, providing more nucleation points
2) horizontal vs vertical boundary layer effect
3) gravity driven vertical diffusion of water vapor effect

Of course these all could be wrong.

Does anyone know the correct answer?
 
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  • #2
Does writing "4) other" justify saying you can come up with four explanations?
 
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mjc123 said:
Does writing "4) other" justify saying you can come up with four explanations?

Corrected, although I think recognizing my own ignorance is worth something.
 
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  • #4
Was that true of ALL vertical glass or just of that glass facing a tree or a man-made structure?
 
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  • #5
phinds said:
Was that true of ALL vertical glass or just of that glass facing a tree or a man-made structure?

It holds for all ALL vertical glass.

It also holds for the car body. Hood, roof, trunk had frost. The rest did not.

The surrounding ground/concrete was frost free.
 
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  • #6
Frost forms from radiative loss of heat cooling a surface. Plus radiative loss occurs more rapidly on surfaces with an unobstructed "view" of the night time sky and no other potentially radiating objects nearby, e.g., houses, walls. Does that help somewhat?
 
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  • #7
It does help. The front windshield faced a brick wall (5 ft) of an unheated garage. The right side was 5 ft from a wood fence. The left side was 20 ft from a brick house. Is radiative cooling that view sensitive?
 
  • #8
I agree that it probably is mainly radiative cooling. Frost occurs because an object is colder than the surrounding air and therefore the water vapor in the air condenses on that surface (air has to be humid enough). The main (only?) way to get a surface colder than the surrounding air is via radiation.

Non-vertical windows have a normal component towards the sky, to which a lot of heat can be radiated away.
 
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1. Why does frost preferentially form on non-vertical car windows?

Frost forms on surfaces when the temperature of the surface is below the dew point of the surrounding air. Non-vertical car windows, such as the windshield and rear window, are more exposed to the cold air and therefore cool down faster, causing the dew point to be reached more quickly and resulting in frost formation.

2. What factors affect the formation of frost on car windows?

The main factors that affect the formation of frost on car windows are temperature, humidity, and wind speed. Lower temperatures and higher humidity levels increase the likelihood of frost formation, while wind can disrupt the formation of frost by mixing the air and preventing the surface from cooling down.

3. How does frost affect visibility while driving?

Frost on car windows can significantly reduce visibility while driving. It can make it difficult to see other vehicles, traffic signals, and road signs, increasing the risk of accidents. It is important to remove all frost from the windows before driving to ensure safe visibility.

4. Can frost damage car windows?

Frost itself does not typically cause damage to car windows. However, if the frost is not removed properly, it can create pressure on the glass and potentially cause cracks or chips. It is important to use proper techniques, such as using a scraper or de-icing solution, to remove frost without damaging the windows.

5. How can I prevent frost from forming on my car windows?

There are a few ways to prevent frost from forming on car windows. One way is to park the car in a garage or covered area to protect it from the cold air. If that is not possible, you can cover the windows with a tarp or blanket to insulate them. Additionally, using a de-icing solution or turning on the defroster can help melt existing frost and prevent new frost from forming.

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