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Thread: Car Travel

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    Platinum Lounger
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    Re: Car Travel

    Fog is the fine condensation of moisture from the air on the cold surface of the windscreen.

    1) The moisture (largely) from your breath condenses on the cold windscreen.
    2) The air conditioner pumps out dry (dehumidified) air that "soaks" the moisture up.
    3) The heater blows sufficiently hot air to re-evaporate the condensation.
    4) Opening the windows might do a couple of things - introduce cold outside air that won't deposit moisture on the (equally) cold windscreen and/ or introduce less humid air.
    5) Not sure. This might be the accumulation of outside condensation, forced to the bottom by the moving air.

    I know that the best way to demist is by running BOTH the air cond and the heater together at full blast, producing dry, hot air. It also gives the air cond a winter workout, keeping all the parts moving occassionally.

    Alan

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    WS Lounge VIP sdckapr's Avatar
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    Re: Car Travel

    Alan answered most of the others
    e)Same condensation principle. I think the humid outside air touches the cold bottom part of the windshield (screen). It is usually colder at the bottom since that is where the vents typically blow on it.

    Steve

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    5 Star Lounger Ruff_Hi's Avatar
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    Car Travel

    I was travelling to Canada last week and ran into a windscreen fog issue - I wanted to know the following:

    a) Why does my windscreen fog up?
    [img]/forums/images/smilies/cool.gif[/img] Why does turning on the air conditioner fix the problem?
    c) Why does turning on the heat fix the problem?
    d) Why does opening the windows fix the problem?
    e) Why do I get condensation at the bottom of the outside of the windscreen?

    Its not a real puzzle but I'm sure that this lounge can supply these answers?
    (Location Australia, then UK, but now USA. Heart, outlook, attitude, etc always Australian)
    Quote: "All Happiness is the release of internal pressure"

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    5 Star Lounger Ruff_Hi's Avatar
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    Re: Car Travel

    and I forgot to add ...

    f) what is the white fog stuff that sometimes comes out the vents? - what causes it?
    (Location Australia, then UK, but now USA. Heart, outlook, attitude, etc always Australian)
    Quote: "All Happiness is the release of internal pressure"

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    Re: Car Travel

    Water vapor condensation (fog)

    Steve

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    Re: Car Travel

    How old is the car? The heater coil might be going out. (I learn car stuff from my husband. He learns about gardening from me.) I am not a car person, much less someone that works on them but the Click and Clack car show on NPR is hilarious, they also answer questions about car problems.
    <img src=/S/whisper.gif border=0 alt=whisper width=29 height=17> We call them windshields in the States. (Well maybe, I don't know what the yankees (as apposed to southerners) call them.

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    Re: Car Travel

    One point I don't think covered by the others was the effect of switching to recycling the air in the car, as opposed to having fresh air coming in. This can be a mixed blessing; on one hand you are heating air already warmed, on the other, it is getting more and more humid as you breath out into the same air.
    I've often been caught out by this on coolish days, when the heater/ACC isn't running too high, but the outside air is cold enough to cool the windscreen. Other things to take into account that cause excessive 'fogging' are wet or damp clothes, bawling children and hot and wet hairy dogs.

    (We call windscreens "windscreens" in the UK) <img src=/S/smile.gif border=0 alt=smile width=15 height=15>

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    Re: Car Travel

    Is that the same thing as a low flying cloud?
    (Location Australia, then UK, but now USA. Heart, outlook, attitude, etc always Australian)
    Quote: "All Happiness is the release of internal pressure"

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    Re: Car Travel

    Thanks All. I guess this is another word that I need to add to my <img src=/w3timages/censored.gif alt=censored border=0> list of things that draw a blank stare. I ran into another one yesterday when talking about a power point, I was talking about the "earth" wire and the other guy was talking about the "ground" wire. No doubt you are going to tell me that it isn't called a power point either.

    One thing that I was thinking about re condensation on the outside is that I would expect that the air pressure at the base of the windscreen / shield is highest at the bottom because of the wind rushing over the bonnet / hood is being pressed against the glass / glass?. What happens to the air's ability to contain water at higher pressures?
    (Location Australia, then UK, but now USA. Heart, outlook, attitude, etc always Australian)
    Quote: "All Happiness is the release of internal pressure"

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    Re: Car Travel

    Electric socket?

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    Re: Car Travel

    There is always vapor in the air (humidity). There is more in summer than winter and when it comes in contact with a colder surface, if the amount the cooler air can hold is less, the vapor will come out of solution.

    Steve

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    Re: Car Travel

    <hr>....when talking about a power point........<hr>
    And if you were talking about a power point to me, I would automatically think of the software - MS PowerPoint and wonder what kind of presentation you were working on???? <img src=/S/grin.gif border=0 alt=grin width=15 height=15>


    "Peace begins with a smile. "-- Mother Teresa

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    Re: Car Travel

    If the "white fog stuff" is combined with a rapid increase in temperature and a burning smell then your car is on fire. <img src=/S/fire.gif border=0 alt=fire width=15 height=15>

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    Re: Car Travel

    <img src=/S/rofl.gif border=0 alt=rofl width=15 height=15>

    Though it is usually "black fog" not white due to all the carbon.

    Steve

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    Re: Car Travel

    Actually, my memory of this is white, choking fumes. It was in the first car I had, which used metal "inline" fuse holders, and (post mortem) the metal case had chewed its way through the insulation causing a dead short. It happened under the dashboard and the smoke from the burning insulation poured up from the bottom of the windscreen, reducing visibility to zero immediately. Lucky - no crash.

    Alan

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