SilverLexus
Super Enthusiast
Just curious. Thanks!
Is there a quality anti-fogging product for windows?
- Thread starter SilverLexus
- Start date
SilverLexus
Super Enthusiast
My AC is fine...I'm doing this for a friend.
White95Max
New member
Keep the vents blowing fresh air. If you keep the relative humidity inside the car at less than 100%, you won't have water vapor condensing on the glass.
Water vapor can condense out of the air onto glass even if the relative humidity inside the car is < 100%. All it takes for condesation to form is to have the temperature of the glass to be just below the dewpoint of the incoming air. The dewpoint is the temperature at which the incoming air is saturated with water vapor. Whenever you cool the glass just below this temperature, you will have condensation forming on the glass. Just think of a glass of water with ice cubes in it.
I think most are familiar with the original Rain-X antifog treatment and IMO it is crap. Unless they have changed/updated their original formula since I tried it long ago, I believe that's why Lee was asking for a quality alternative.
I think most are familiar with the original Rain-X antifog treatment and IMO it is crap. Unless they have changed/updated their original formula since I tried it long ago, I believe that's why Lee was asking for a quality alternative.
White95Max
New member
Yes, but why would the temperature inside the car be less than the ambient temperature outside? If you say when the A/C is running, then the humidity in the interior would be lower as well.
Most of the time when people complain about fogging on the interior glass, it's immediately after startup, when the temperature inside the car is equal to the temperature outside, but the water vapor from the person's breath is raising the relative humidity inside the car. If the atmospheric conditions already include high relative humidity levels, it won't take much water vapor to raise the relative humidity inside the car to 100%. Keeping the vents blowing fresh air into the interior will actively work to prevent the humidity from reaching 100%.
There's also the chance of creating localized pockets of 100% humidity inside, by breathing directly on the glass. This can be somewhat prevented by exhaling through your nose, to direct the air downward rather than outward toward the glass by mouth breathing.
Most of the time when people complain about fogging on the interior glass, it's immediately after startup, when the temperature inside the car is equal to the temperature outside, but the water vapor from the person's breath is raising the relative humidity inside the car. If the atmospheric conditions already include high relative humidity levels, it won't take much water vapor to raise the relative humidity inside the car to 100%. Keeping the vents blowing fresh air into the interior will actively work to prevent the humidity from reaching 100%.
There's also the chance of creating localized pockets of 100% humidity inside, by breathing directly on the glass. This can be somewhat prevented by exhaling through your nose, to direct the air downward rather than outward toward the glass by mouth breathing.
White95Max said:
Paul, I understand where you're coming from and I should have been more specific. I guess I'm just too used to having the following happen in the humid environment of Louisiana. You can also get condensation to form on the *outside* of the windshield by having cold air (ac) blowing on the inside of your windshield. This is the phenomenon that I was trying to describe earlier.
Sorry for the threadjack science/meteorology lesson.
imported_MCA
New member
chml17l said:
I second this opinion. I tried the Rain-X Antifog product several years ago - It did not work well at all for me. Although it did prevent fog, it left a faint haze that I could not get rid of...very similar to "dirty" interior window haze. On top of that, durability was not a good point. They may have changed their formula since I last tried so things might be different this time around, but I wouldn't have your hopes up.
White95Max
New member
chml17l said:Paul, I understand where you're coming from and I should have been more specific. I guess I'm just too used to having the following happen in the humid environment of Louisiana. You can also get condensation to form on the *outside* of the windshield by having cold air (ac) blowing on the inside of your windshield. This is the phenomenon that I was trying to describe earlier.
Sorry for the threadjack science/meteorology lesson.
Couldn't you easily remedy this problem by switching the vents to blow A/C through the front or floor vents, rather than the defroster vents? Or maybe set it to floor/defrost so that only part of the A/C gets to the windshield?
I love science/meteorology, so no harm done.
It would be best to know when the fogging problem occurs.
I know many people who use the heater inside of the car without using the A/C on. This creates a problem since it makes the interior more humid. My A/C button is always on whether or not I am using it to heat or cool. The dry air that it provides makes a difference.
I am in Louisiana as well so I am familiar with humidity
I also have to give the :down to RainX anti-fog. I tried it once and it didn't work, nothing like their exterior repellent.
I know many people who use the heater inside of the car without using the A/C on. This creates a problem since it makes the interior more humid. My A/C button is always on whether or not I am using it to heat or cool. The dry air that it provides makes a difference.
I am in Louisiana as well so I am familiar with humidity
I also have to give the :down to RainX anti-fog. I tried it once and it didn't work, nothing like their exterior repellent.
White95Max
New member
twitch said:
Heating the air makes it LESS humid.
Example:
At 15*C the air can hold 11g of water vapor per kilogram of air.
At 20*C the air can hold 15g of water vapor per kilogram of air.
These are scientific numbers, not just random numbers pulled out of my head.
It could possibly indirectly make the air inside more humid by causing the passenger(s) to sweat. The perspiration evaporating from their skin would add to the water vapor content of the air.
White95Max said:
interesting, good to know. I wouldn't take you as a person to pull these numbers outta your head
I don't know the science behind it but I do know that in every instance either in my car or someone elses having the A/C on was the only way to keep the interior fog free.
This is in the Louisiana winter when the temps are in the 30s-50s and the humiditiy outside is fairly high. If the heater is used without the A/C the windows will stay fogged, use the A/C and the windows stay clear.
SilverLexus
Super Enthusiast
Getting back to the first post...Does anyone know of a good anti-fog product?
zippymbr
New member
I use spit inside my scuba mask, works great! LOL Sorry I could not resist.
White95Max
New member
twitch said:interesting, good to know. I wouldn't take you as a person to pull these numbers outta your head
Living in Louisiana, you surely know that hurricanes are most frequent in the summer and fall. That's because the air over the oceans is hottest at that time, and thus can hold the most water vapor. A hurricane gets its power from the "latent heat of evaporation" of water. Water is evaporated from the ocean, which takes heat energy to do so. Since energy cannot be created or destroyed (First Law of Thermodynamics), it is carried with the water vapor in the form of latent heat (2,270 kilojoules per kilogram of water vapor). When this water vapor rises with the air, cools, and condenses to form clouds, it releases the latent heat of condensation, heating the air around it, which then rises further, creating massive clouds if there is a steady supply of water vapor available. This causes the "boiling" appearance of violent thunderstorm clouds.
I forget where I was going with this. Anyway, hot air has a higher ability to hold water vapor than cooler air!
White95Max said:Anyway, hot air has a higher ability to hold water vapor than cooler air!
Then wouldn't this mean that heating the air would make it MORE humid, not less?
And now that I look at the numbers you posted again it that would make sense due to the higher temperature having the ability to hold more water vapor.
SilverLexus - certainly not trying to stomp on your thread. I do think it would be important to find out what kind of fogging issues your friend has.
imported_NT2SHBBY
New member
SilverLexus said:
in case you haven't realized I will lay it out for ya
Just tell your friend to run his a/c compressor, that will stop the fogging...now if your friend doesn't have one or it's broken, tell him/her to get it fixed/replaced/installed.
oh yes and uh....
rain-x anti-fog sucks big donkey balls because not only does it leave a nasty clearish haze, but it makes for driving at night (especially in the rain) horrible because of the aweful reflection of the dash is on your windshield at eye level
:bigups
White95Max
New member
twitch said:
Nope. Let's take 1kg of air at 15*C for example. It has the ABILITY to hold 11g of water vapor. At saturation, it holds 11g. Let's say at a particular time it's holding 8g of water vapor. That means the relative humidity is 8g / 11g = 72.7%.
As you heat the air, the water vapor is not changing. If you were to heat the same 1kg of air to 20*C, it has the ABILITY to hold 15g. It is still only holding 8g of water vapor though. So now you have a relative humidity of 8g / 15g = 53.3%.
Think of the morning fog. You see fog in the morning because the temperature has dropped overnight, and unless a cold front has moved through, the water vapor content of the air is likely to be the same as it was the evening before. The air cools, the relative humidity increases, and fog forms as the air reaches saturation (100% relative humidity). As the morning sun heats the air and the earth's surface, the fog begins to lift. As the air near the ground heats up, the relative humidity becomes less than 100%, and the fog dissipates.
