 Poster: A snowHead
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Do you wear a helmet? I can't say that foggy goggles is a problem that bothers me 99% of the time. The exception being very specific temperature/weather combinations which are usually down to a very large temperature gradient on the mountain and very high humidity. and goggles I'm talking about include bog standard basic double lens Smith and Scott rather than £200 Oakleys.
Hiking is a bit of a different issue. Best to carry a pair of sunnies for that.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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| fatbob wrote: |
| Do you wear a helmet? I can't say that foggy goggles is a problem that bothers me 99% of the time. The exception being very specific temperature/weather combinations which are usually down to a very large temperature gradient on the mountain and very high humidity. and goggles I'm talking about include bog standard basic double lens Smith and Scott rather than £200 Oakleys. |
Due to gravity there will always be about the same temperature gradients on hills?
I don’t get misted up goggles very often. Normally just when I move em up onto my hat for reason or other.
Foggy goggles are almost never caused by the weather conditions – as the Dew point will be higher on the inside then the outside due to someone wearing them. It MAY be that the goggles will be more prone to misting in certain conditions, but it is not the conditions that do the actual “misting”.
Mist on the inside is “almost always” caused by extra water getting into the space between the lens and the face (snow, rain, breath, sweat, etc). Eg. If you wear you goggles with a gap in the padding your breath can enter the air space and increase the moisture level. If you head-butt the floor and get snow inside your goggles, if it snowing and snow lands on the padding and then melting through the form, etc, etc.
Of course if you're skiing down a hill you will have an airflow through the vents, if you happen to stop then the flow disappears and the Dew Point will rise (as your face is putting out "stuff"), so you get mist – it not the weather conditions that cause it in this case but the fact that you stopped (so got rid of the flow).
The higher the moisture level, the higher the Dew Point, this combined with the fact the Dew Point is “always” lower than the air temperature, means that if you increase the moisture content the Dew Point will go up until it is the same as the air-temp and you get condensation. Note that (contrary to what you read on many, many website and way too many school text books ??) the air temperature has nothing the do with the Dew Point.
I do think that many people speculating about this in the press are not skiers? (or physicists) as if they were either they would know the lenses tend to be double in most modern ski goggles. This means that the inner lens will act as a Thermal Bridge for the wind effect on the outer lens. Oh well.
Of course there are times where the weather could possibly cause misting. E.g. when there are breaks in some cloud cover. This would have the effect of (as you went into a cloudy moment) of reducing the outside temperature so that the Thermal Bridge effect on the lens may reduce the difference between the air temp and the dew point inside the goggles.
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Have been going back over the patent application again and it seems they are (without actually saying so - as you can't patent it ??) relying on the thermodynamics of the relationship between the volume to surface area. But, good luck to em, plenty of other people make shed loads of cash from the 1st L of T (wish I coud come up with something, dragon's den, here I come  .
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Last edited by Well, the person's real but it's just a made up name, see? on Fri 6-07-12 12:37; edited 2 times in total
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If you have real misting up problems, just boil down fairy liquid until you've turned an entire bottle into a teacup. Wipe a tiny bit of it on the inside of your goggles. That works inside diving masks that are 3 deg outside and toasty warm inside, with no misting. If your goggles still steam up, you have a problem with the goggles.
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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Monium,
Here's an extract from a book wat-i-rote
A well known “home-remedy” used by many skiers is to lightly dab a solution of white vinegar and water (1:20 ratio – water should be warm when mixing) onto the inner lens and allowed to dry without wiping. This has a number of benefits over shop-bought products; it’s much cheaper, it is proven to work in all temperatures, it is non toxic. Users should note that it is vital to allow the solution to completely air-dry prior to use.
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Yep your physics agrees with my anecdotal observations of what happens. You're right to pick up on temperature gradients - usually it's specific temperature gradients - warm and wet at the bottom of a hill , a fast chair takes you above the freezing line and the wetted out foam then conduits water vapour inside the lens to condense on the rapidly cooling lens. I think of it as similar to the rime process although I guess there may be technical differences
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| fatbob wrote: |
Yep your physics agrees with my anecdotal observations of what happens. You're right to pick up on temperature gradients - usually it's specific temperature gradients - warm and wet at the bottom of a hill , a fast chair takes you above the freezing line and the wetted out foam then conduits water vapour inside the lens to condense on the rapidly cooling lens. I think of it as similar to the rime process although I guess there may be technical differences
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What’s happening here is that lower down there is more moisture in the air (it’s that gravity stuff again) and the foam padding (being made from a mixture of diisocyanate and some weird forms of polyol (basically a strong G & T, well I like think it “could” be anyway ) which when combined form polar polymers – so water will covalently bond to it. As the “Holes” in the foam are formed when most of the “stuff” in the PU is reticulated (it’s burned or dissolved out) this forms small enough gaps for the water to creep into it. This process continues until it reaches the other side of the foam when it evaporates (as your face provides the extra energy needed to whizz the h2o bits around faster and break the hydrogen bonds). As you’re on a lift there is a flow through of air pushing this vapour out of the space between your face and the lens. Of course when you stop this flow is removed and the moisture condenses. As the lens is colder than the air (inside the goggles) it reduces the temperature near to it to bring it down to the Dew point and droplets form on the lens.
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FAQ
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(let's wait and see what happens)
