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John of Phoenix
01-12-2016, 01:11 PM
Yesterday morning I started up the car and turned on the windshield wipers to get the dew off the windshield. The wipers just skimmed over a layer of ice. The thermometer said it was 37F. Ok, who knows how accurate the reading was, maybe the temp was 32.

Today I went out and again, there was dew on the windshield. I ran my finger across the windshield and it was in fact liquid but the moment I turned on the wipers, it turned to ice. Again the temp read 37. It seems odd that the water would turn to ice simply because... of what?

Norman Bernstein
01-12-2016, 01:16 PM
Today I went out and again, there was dew on the windshield. I ran my finger across the windshield and it was in fact liquid but the moment I turned on the wipers, it turned to ice. Again the temp read 37. It seems odd that the water would turn to ice simply because... of what?

The wipers exposed more 'surface' of the dew, to the air, and the resulting evaporation lowered the temperature enough to form ice. This only happens if the air is dry enough, though.

Old Dryfoot
01-12-2016, 01:18 PM
Reducing the amount of water on the windshield allowed what remained ( a thinner layer) to freeze?

Smaller bodies of water will freeze before larger ones, maybe that was at play in this case.

Daniel Noyes
01-12-2016, 01:19 PM
Yesterday morning I started up the car and turned on the windshield wipers to get the dew off the windshield. The wipers just skimmed over a layer of ice. The thermometer said it was 37F. Ok, who knows how accurate the reading was, maybe the temp was 32.

Today I went out and again, there was dew on the windshield. I ran my finger across the windshield and it was in fact liquid but the moment I turned on the wipers, it turned to ice. Again the temp read 37. It seems odd that the water would turn to ice simply because... of what?

sounds like the dew was super cooled, if water or similar is cooled slowly and is not agitated it can cool below freezing then freeze when agitated, If you have ever taken a water bottle from the freezer and shaken it and it is liquid then you go to drink it and it is frozen in a stiff slush similar phenomenon!

also the car window may be radiant cooling, like a solid object can be hotter on a bright sunny day than the air, an object ca be radiant cooled by the blackness of space on a clear night and surfaces can be below air temp :)

Gerarddm
01-12-2016, 01:21 PM
Speaking of which, saw an article that said if you mix up alcohol and water in a 1/3- 2/3 ratio in a spray bottle, it will almost instantly defrost a windshield without using a scraper or waiting for the car defroster to work.

I have always wondered why car manufacturers don't simply have auxiliary electrical heating elements in their blowers so you can instantly start getting heat onto your windshield as soon as the motor is started. It takes a long time for my diesel to heat up.

John of Phoenix
01-12-2016, 01:51 PM
Speaking of which, saw an article that said if you mix up alcohol and water in a 1/3- 2/3 ratio in a spray bottle, it will almost instantly defrost a windshield without using a scraper or waiting for the car defroster to work.

I have always wondered why car manufacturers don't simply have auxiliary electrical heating elements in their blowers so you can instantly start getting heat onto your windshield as soon as the motor is started. It takes a long time for my diesel to heat up.I thought the washer fluid would have that effect but no joy - it just froze too.

Peerie Maa
01-12-2016, 02:37 PM
^ What Daniel said.

John of Phoenix
01-12-2016, 02:46 PM
^ What Daniel said.Supercooled is what I thought this morning and expected that when I ran my finger across the windshield that some of the water would turn to ice from the disturbance but nothing happened until the wipers came into play.

Jim Bow
01-12-2016, 02:48 PM
Any comments on the spray can deicers?
Any residual chemicals? Any damage to finishes?

P.I. Stazzer-Newt
01-12-2016, 02:52 PM
Spray can de-icers drop the temperature of the water and the glass

Hereabouts - idiots hit a thick layer of ice with spray and then the inside of the glass ices up....

If you have to use them - scrape the thick off first.

Peerie Maa
01-12-2016, 02:56 PM
Supercooled is what I thought this morning and expected that when I ran my finger across the windshield that some of the water would turn to ice from the disturbance but nothing happened until the wipers came into play.

You got warm fingers but the wipers are as cold as the dew and the glass.

Figment
01-12-2016, 02:58 PM
I thought the washer fluid would have that effect but no joy - it just froze too.

what? man you're using the WRONG washer fluid!

Peerie Maa
01-12-2016, 03:09 PM
I thought the washer fluid would have that effect but no joy - it just froze too.

The washer fluid sold here has different dilution advice to suit warm or cold temps, is yours strong enough a mix?

John of Phoenix
01-12-2016, 03:32 PM
The washer fluid sold here has different dilution advice to suit warm or cold temps, is yours strong enough a mix?I don't know. It smells like Windex which as I remember is water with a bit of alcohol and ethylene glycol. The dealer refills it when I have the car serviced. I don't use it much here in the desert.

Peerie Maa
01-12-2016, 03:36 PM
I don't know. It smells like Windex which as I remember is water with a bit of alcohol and ethylene glycol. The dealer refills it when I have the car serviced. I don't use it much here in the desert.

Ahh dealers. I once drove a rented car on a business trip in winter, the washer water froze in the reservoir. If they can save a penny by skimping . . . .

Too Little Time
01-12-2016, 03:38 PM
Yesterday morning I started up the car and turned on the windshield wipers to get the dew off the windshield. The wipers just skimmed over a layer of ice. The thermometer said it was 37F. Ok, who knows how accurate the reading was, maybe the temp was 32.

Today I went out and again, there was dew on the windshield. I ran my finger across the windshield and it was in fact liquid but the moment I turned on the wipers, it turned to ice. Again the temp read 37. It seems odd that the water would turn to ice simply because... of what?

It is difficult to get super cooled water at 37 degrees. It is also hard to get enough evaporative cooling at that temperature.

My bet is that the glass was below 32 degrees, but the dew was above 32 and cooling off. When you got rid of most of the dew with the wipers, what was left froze due to normal conductive heat transfer.

Phil Y
01-12-2016, 03:48 PM
If you kept a small bottle of 1/3 alcohol and 2/3 water in the car, at least you could drink it while you wait for the car to warm up. I'd suggest a nice Glenfiddich.

Paul Pless
01-12-2016, 03:49 PM
what? man you're using the WRONG washer fluid!yankee washer fluid is impressive. . .

John of Phoenix
01-12-2016, 03:50 PM
It is difficult to get super cooled water at 37 degrees. It is also hard to get enough evaporative cooling at that temperature.

My bet is that the glass was below 32 degrees, but the dew was above 32 and cooling off. When you got rid of most of the dew with the wipers, what was left froze due to normal conductive heat transfer.Except the water that was swept off by the wipers also froze. Kind of a roll of frost at the edge of the wiper sweep.

John of Phoenix
01-12-2016, 03:52 PM
If you kept a small bottle of 1/3 alcohol and 2/3 water in the car, at least you could drink it while you wait for the car to warm up. I'd suggest a nice Glenfiddich.Now we're gettin' somewhere.

Figment
01-12-2016, 04:01 PM
yankee washer fluid is impressive. . .

http://ecx.images-amazon.com/images/I/410jetmg%2BkL._SY300_.jpg

ACCEPT NO SUBSTITUTE! :D

(and put a tag on your fill cap so the dealer doesn't add watery crap with each oil change)

Curtism
01-12-2016, 04:08 PM
I like the way Phil Y thinks. Y>

John, could wind chill be a factor?

01-12-2016, 04:33 PM
http://ecx.images-amazon.com/images/I/410jetmg%2BkL._SY300_.jpg

ACCEPT NO SUBSTITUTE! :D

(and put a tag on your fill cap so the dealer doesn't add watery crap with each oil change)

Oh yeah, a little more expensive but well worth it!

John of Phoenix
01-12-2016, 04:34 PM
Dead calm, clear sky. We should have similar conditions tomorrow. I have a few ideas for experiments - any ideas?

S.V. Airlie
01-12-2016, 04:48 PM
Darn, I ain't mixing my Glenfiddich with water or any other substance than you very much!:)

Michael D. Storey
01-12-2016, 09:06 PM
Regards the original question, I reckon that the inside of the car was cooler than the outside air, very likely, indeed, considering that the car was still outside all night. I would suggest that the outside-car air was warm enough to melt the ice from the outside. The wipers removed the melted ice, revealing the frozen ice.

pipefitter
01-12-2016, 11:55 PM

Chip-skiff
01-13-2016, 01:22 AM
It is a boggle. In streams, water freezes more quickly in areas where there is turbulence: riffles and rapids. It freezes from the shear zones (i.e. the rocks) outwards, which sounds a bit like the windshield/wiper contact.

Wish I knew the rockbottom physics involved.

Reynard38
01-13-2016, 07:44 AM
Evaporative cooling, or perhaps a situation similar to what we sometimes encourage get when flying. Very tiny droplets of water in clouds can remain liquid at temps well below 0 Celsius. When something comes along to disturb them, say a windshield wiper or the leading edge of a wing they freeze on contact.

Chris Coose
01-13-2016, 06:15 PM
In the old days I diverted one of the truck windshield washer hoses into the cab and plugged the other one. I filled the reservoir with Seagrams. Never froze.

Too Little Time
01-13-2016, 08:46 PM
Except the water that was swept off by the wipers also froze. Kind of a roll of frost at the edge of the wiper sweep.

If I run my wipers when there is ice on the windshield, a roll of "frost" appears as you observed.

While there seem to be a number of opinions, most require conditions other than those in your original post.

For evaporative cooling to freeze the remaining water would almost certainly require the glass to be below freezing. For super cooling to freeze teh water, the windshield would need to be much cleaner than possible and the temperature of the water to be much lower than ambient.

But it could be that there was a layer of ice below the surface. That would require the glass to be below freezing.