Frost preferentially forms on non-vertical car windows?

  • Context: Undergrad 
  • Thread starter Thread starter Frabjous
  • Start date Start date
  • Tags Tags
    Car Forms Windows
Click For Summary

Discussion Overview

The discussion centers around the phenomenon of frost formation on car windows, specifically examining why frost appears to form preferentially on non-vertical windows. Participants explore various explanations related to environmental factors and physical principles, including radiative cooling and surface conditions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests three potential explanations for frost formation on non-vertical windows: dirtier surfaces providing more nucleation points, boundary layer effects, and gravity-driven vertical diffusion of water vapor.
  • Another participant questions the validity of counting a fourth explanation as "other" without further elaboration.
  • It is noted that frost formation may depend on the orientation of the glass relative to nearby structures, with one participant asserting that the phenomenon holds for all vertical glass.
  • A participant explains that frost forms due to radiative heat loss, which is influenced by the unobstructed view of the night sky and the presence of nearby radiating objects.
  • Another participant inquires whether radiative cooling is sensitive to the view of the surrounding environment, given the proximity of the windshield to various structures.
  • One participant agrees that radiative cooling is likely the primary mechanism for frost formation, emphasizing that non-vertical windows can radiate heat more effectively towards the sky.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms behind frost formation, with some focusing on radiative cooling while others propose alternative explanations. The discussion remains unresolved, with no consensus on the primary cause of the observed phenomenon.

Contextual Notes

Participants mention various factors that could influence frost formation, such as surface cleanliness, proximity to structures, and environmental humidity, but these factors are not fully explored or quantified.

Frabjous
Gold Member
Messages
1,968
Reaction score
2,432
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?
 
Last edited:
Physics news on Phys.org
Does writing "4) other" justify saying you can come up with four explanations?
 
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.
 
  • Haha
Likes   Reactions: berkeman
Was that true of ALL vertical glass or just of that glass facing a tree or a man-made structure?
 
  • Like
Likes   Reactions: Frabjous
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.
 
  • Informative
Likes   Reactions: phinds
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?
 
  • Like
Likes   Reactions: berkeman, Frabjous and russ_watters
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?
 
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.
 
  • Like
Likes   Reactions: Frabjous

Similar threads

  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 9 ·
Replies
9
Views
9K
Replies
2
Views
1K
  • · Replies 21 ·
Replies
21
Views
6K
Replies
2
Views
8K
  • · Replies 1 ·
Replies
1
Views
5K
Replies
4
Views
4K
  • · Replies 11 ·
Replies
11
Views
4K
  • · Replies 1 ·
Replies
1
Views
5K
Replies
26
Views
9K