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garyphansen
02-25-2006, 02:04 PM
On her way home last night my daughter hit some black ice and flipped her car. It ended up upside down in the ditch in three feet of snow.
She was not hurt and thhe only damage was a broken window and a mirror. The tow truck diver said it probaly wrecked the engin from bing upside down for an hour. He started it and it died.
My thought is there is oil on the cylinders and taking the spark plugs out and turning the car over a few times will correct it. I am looking for some advice on this. Gary P. HHansen

Carl
02-25-2006, 02:18 PM
First, thank GOD your daughter is okay.(Was she wearing her seatbelt?). If the engine didn't run upside down for an extended period of time it should be okay. My friend back in high school bought a '37 Ford with a 283 chevy in it from a guy that was deaf. He said the engine ran real rough. We took it home and pulled the pan. The front two connecting rods were broken. We decided to run the engine without the pan (no oil) and see how long it would take to seize up. We let it idle for a while and nothing happened so we revved it up and still nothing. We finally got bored and gave up. We were quite amazed that we couldn't get it to seize. Seems an engine (at least a small block Chevy) with no load on it will go quite a while with no oil and no load on it.

Wirecutter
02-25-2006, 02:47 PM
Glad to hear that your daughter is ok.

Dawai
02-25-2006, 02:47 PM
But, you can't hook a tow truck to them and drag them backwards in gear..

Craps up the engine in a couple blocks.

HWooldridge
02-25-2006, 03:42 PM
Seven or eight years ago, I flipped a Ford truck on its side off a small bridge in a rain storm. The truck was almost keeling over on its top but stopped just short. Same type deal - no damage to anything, I wasn't going very fast so it landed in the mud and stopped. I had my wife and 3 boys inside, it took two of us to push the door open since all the weight was trying to shut it. I turned off the engine and we all climbed out to wait for the tow truck, which took a couple of hours because we were in the country. I had it towed home and let it sit for the night, then drained and changed all fluids the next day. It fired up fine and I still drive it today.

If the cylinders are clear, I doubt anything is damaged on your daughter's car.

topct
02-25-2006, 05:06 PM
If it's a newer car it propably tripped the impact switch that shuts off the fuel pump.

It started because there was still some pressure in the lines.

It will have to be reset. Maybe a simple disonnect the battery and reconnect?

IOWOLF
02-25-2006, 05:12 PM
It will say in the owners manual where th auto shutoff is.

------------------
The tame Wolf !

Tim125
02-25-2006, 05:31 PM
I'm glad your daughter's ok. The fuel shutoff switch if equiped usually requires a manual reset. As far as the engine it should be ok if none of the cylinders had much oil in them when the driver started it, I've seen rods bent that way.

TECHSHOP
02-25-2006, 10:05 PM
Glad to hear your daughter is alright. Hopefully your daughter isn't too "shaken up" to drive again, and there is no hidden damage that will show up later.

We have had a mild winter so far locally, but it hasn't keep the fatality rate low.

spope14
02-25-2006, 11:07 PM
Fuel shut off, yes. I set mine off when I got "curbed" by a person who cut me off in traffic. The curbs here are granite, 6 inch high straight up things, thus the impact shut me off ASAP (Ford Ranger) and the front wheels were also bent.

As for the oil situation, I saw this once. The trick was to try and suck stuff out with a small shop vac nozzle end first. Next, drain the oil in the pan, usually about two days later to let things settle out. Check for Antifreeze. Then re-fill with three quarts, not four. Try to start things up, then check your dip stick for levels and color to see if you have more drain out. You may blow some oil out the pipe, maybe not. If things get going, then continue checking levels, and fill to proper levels within a reasonable time, say five minutes of running. Check your plugs for fouling as well. Oil will immediately try to burn onto the plugs if it is there, and will foul stuff up.

You may want to do a second oil change within about 50 miles for mental assurance, and in case you start to show coolant of just have plain old junk in the cylinders. You also want to check plugs again, and if you want the mental assurance, change them out again.

Keep an eye on things a few weeks.

This is what I did when I had to fix a friends mustang that did a one and 1/2 into three feet of snow. Worked.

Allan Dimmock
02-26-2006, 04:27 AM
I was on a run once with four other bikers. None of us knew the road and we came across a sudden bend. The first bike ended up upside-down in a tree, the second and third (mine) parallel parked in a ditch and the forth was dropped by the guy at the back because he was laughing so much. When we picked ourselves up and stopped laughing, we pulled the first bike out of the tree, pulled the air filter (that was soaked in oil) and got it going again without any further problems. Probably would have been more serious for the bikes that went into the ditch if that ditch hadn’t been dry at the time. Internal combustion engines are pretty robust.

Friend of mine crashed her car on ice about a month ago. It seems she hit some black ice. The problem is that, on a salted road, patches of ice will still form where wind chill takes the temperature below the freezing point of brine (-7C, if I remember correctly). If the wind changes direction, a previously safe road can become an ice rink. Her accident was on a main road. It seems that she was the unlucky one that found the ice first. Of course, she thought she was safe to drive normally because the rest of the road was OK.

alrednek
02-26-2006, 12:58 PM
<font face="Verdana, Arial" size="2">Originally posted by Allan Dimmock:
[B]
The problem is that, on a salted road, patches of ice will still form where wind chill takes the temperature below the freezing point of brine (-7C, if I remember correctly). If the wind changes direction, a previously safe road can become an ice rink. B]</font>

Not trying to be argumentative, but...wind chill has no effect on water, brine or any other inanimate object. The wind chill factor only approximates the effect the wind has on skin and how cold it feels at a given temperature and wind speed. So, regardless of how hard the wind blows it will have no effect on whether the brine freezes or not-temperature alone will determine that. My uncle, a physics professor, taught me that fact years ago and I sometimes point it out to people just to enlighten them as he did for me. I've listed a couple of references below:

http://www.usatoday.com/weather/resources/askjack/2002-12-01-answers-wind-chill_x.htm

http://www.cbc.ca/news/background/forcesofnature/windchill.html



[This message has been edited by alrednek (edited 02-26-2006).]

spope14
02-26-2006, 01:32 PM
It is not so much wind chill as it is that the areas that are affected by wind are often times hit by sun during the day due to the areas open nature, which causes ice to melt into the road off the snow on the sides, thus causing more water on the road. These areas are also affected by snow blowing into the road.

HWooldridge
02-26-2006, 02:53 PM
A 30 mph wind at 20 degrees is not colder than 20 degrees in still air - but it will take a surface to the freezing point quicker because it's removing ambient heat at a faster rate. In other words, if your water pipes are at 60 degrees during the day while the sun is shining and the temp drops below freezing at night, they will freeze more quickly if the wind is blowing. Everything is trying to reach equilibrium, so exposed pipes and bridges freeze faster than the road because the wind can remove the sun's heat more quickly.

Alistair Hosie
02-26-2006, 03:29 PM
about four years ago Christmas eve I had loaned my new car three weeks old 300miles on clock to my youngest son Russell.He had to go to the hospital about 50 mioles from my house on Christmaqs eve as he is a doctor and was on duty then.On the way there he left the road in an avalanche and skidded across the road and down a very steep embankment down a grassy slope and crashed onto a giant ten toot high boulder and landed in the river. He walked out totaly unhurt he reckons the air bag saved him certain death.So I am pleased to hear your daughter like my son are alive to tell the tale god bless Alistair

debequem
02-27-2006, 10:29 AM
That is not quite true. The wind chill effect is when water (or liquid) evaporates from a surface. The evaporation draws the heat energy it needs (latent heat) from the surface the liquid resides on. The effect of the wind is to speed evaporation by lowering the humidity over the site of evaporization.

In order for a wind chill effect to work there must be a liquid to evaporate. On skin that is typically perspiration, but can be water from rain, snow, or the pool.

Another proof that that wind chill works on inanimate objects is the wet/dry bulb thermometer.


<font face="Verdana, Arial" size="2">Originally posted by alrednek:
Not trying to be argumentative, but...wind chill has no effect on water, brine or any other inanimate object. </font>

ahidley
02-27-2006, 10:43 AM
The inertia switch is usually located near the fuel tank. I believe its only on cars with electric fuel pumps. (except subarus) I've seen them inside the rear quarter panel next to the tank. I've also seen them inside the trunk behind a removable cardboard panel. Just follow the wires from the electric fuel pump

And YES its a manual reset.

[This message has been edited by ahidley (edited 02-27-2006).]

debequem
02-27-2006, 10:56 AM
I'll be sadistic and add some more information on wind chill, just because I can...

Normally wind chill is considered as an effect on the skin, but the principle is the same for any surface that has a liquid like water on it. Normally, that surface is not above the boiling point for water. So how does water evaporate? In order for the water to evaporate it must source heat energy from the neighboring tissue or surface to reach the point of evaporation. The sweat has a temperature close to 100 degrees F, but needs additional energy to evaporate. Essentially, the sweat molecules draw that energy, in the form of heat, from the body tissue. It can do the same from any other surface.

This process is called the enthalpy of vaporization. In order for a liquid to change state to a gas it must overcome the intermolecular chemical bonds that maintain water as liquid; hydrogen bonding in this case. Hydrogen bonding is weak, but still requires energy to break the bonds. The amount of energy required is dependent on the current energy state (i.e., 100 degrees F for sweat) and the energy required for vaporization (212 degrees F). The energy needs to come from somewhere in the form of heat and the thermal conductivity of human tissue or almost any solid surface is much better than surrounding air, so the bulk of it comes from the human body as it is transferred from tissue to the water molecules.

I believe that what your professor meant was that the wind will not chill material that is dry because no evaporization can take place. However, if you place liquid water on the surface of that material, the evaporation will lower the surface temperature of that material. That is exactly how a dry/wet bulb thermometer works.

Evan
02-27-2006, 11:01 AM
"Another proof that that wind chill works on inanimate objects is the wet/dry bulb thermometer."

The wet/dry bulb thermometer doesn't depend on wind chill to work. In fact, when installed outside they are protected from wind. It measures the cooling caused by evaporation. Wind chill only speeds that cooling, it does not increase it by degree. Wind will speed the cooling of a puddle of water but once the water reaches ambient temperature an equilibrium condition is reached and no further temperature drop will occur. If this were not the case then water would freeze when exposed to wind regardless of ambient temperature.

The freezing point of a eutectic brine mixture (26.4%) is -6F or -21C. This is a saturated brine solution. More or less salt results in a higher freezing temperature. A 15% brine solution freezes at about 20F (-7C).

[This message has been edited by Evan (edited 02-27-2006).]

debequem
02-27-2006, 11:45 AM
I would agree, but the evaporative principle that cools the skin is the exact same principle that cools the wet bulb. That was why I cited it as an example.

If you were to remove the wind guard from the wet/dry thermometer the delta temperature would be even greater if there was a wind.

The bottom line is that evaporative cooling is accelerated when there is a wind, but only by carrying away water vapor at the localized site of evaporation and reducing the relative humidity at the site of vaporization. On a micro level, when part of a water droplet evaporates, the air in proximity to the water drop becomes momentarily saturated and evaporation halts. Wind speeds the dissipation of the water vapor so evaporation can continue. This assumes that the ambient relative humidity of the air is less than 100%.

There is a limit to the range of conditions that this effect will work as well as the rate that it will work. Obviously if the relative humidity is 100% there can not be evaporation. Conversely, in an arid climate the rate of evaporation is much faster and the warmer the ambient air is, the lower the effect of wind speed has on wind chill.

The last portion of your point is a little fuzzy, but I think you are speaking about convective cooling, which is a different matter altogether.

For humans, there is one other complicating variable. Humans generate heat, which typically is trapped between the skin and clothing. If the ambient temperature is lower than the surface temperature of the skin, wind will substitute cooler air for the warm air trapped beneath the clothes or at the boundary layer over the skin. Even if evaporation does not take place, the cooler ambient air will chill you by convection.

Great post, Evan.


<font face="Verdana, Arial" size="2">Originally posted by Evan:
"Another proof that that wind chill works on inanimate objects is the wet/dry bulb thermometer."

The wet/dry bulb thermometer doesn't depend on wind chill to work. In fact, when installed outside they are protected from wind. It measures the cooling caused by evaporation. Wind chill only speeds that cooling, it does not increase it by degree. Wind will speed the cooling of a puddle of water but once the water reaches ambient temperature an equilibrium condition is reached and no further temperature drop will occur. If this were not the case then water would freeze when exposed to wind regardless of ambient temperature.

The freezing point of a eutectic brine mixture (26.4%) is -6F or -21C. This is a saturated brine solution. More or less salt results in a higher freezing temperature. A 15% brine solution freezes at about 20F (-7C).

[This message has been edited by Evan (edited 02-27-2006).]</font>

lynnl
02-27-2006, 11:53 AM
Evan, your comment "..The wet/dry bulb thermometer doesn't depend on wind chill to work..."

is wrong, as it pertains to the old traditional Sling Psychrometer.

The ventilation across the saturated wick accomplished the same process that wind blowing across the skin accomplishes. It facilitated maximum evaporation of the distilled water absorbed within the wick surrounding the wetbulb thermometer, thereby using the latent heat of evaporation to depress the wetbulb thermometer reading below the ambient temperature, by an amount dependent on the ambient humidity (as well as atmospheric pressure).
(The objective being, of course, to calculate the ambient humidity, or "Dewpoint temperature depression".)

Modern temp/dewpoint measuring equipment does it differently. But weather stations still retain a sling psychrometer as a backup, and for test and calibration purposes. Or at least they did when I retired from weather service in 1987.


(added) debequem's post entered while I was typing, gives a good description of the process.

[This message has been edited by lynnl (edited 02-27-2006).]

Evan
02-27-2006, 12:23 PM
You are right, my explanation is not complete. The wet bulb temperature is actually defined as how much the temperature of air can be reduced by the addition of water and is not dependent on wind. When the temperature falls because of the addition of water vapor to a volume of air thereby raising the humidity the total heat content per unit volume of air remains the same. In order to bring that air below freezing still requires the removal of the same amount of heat.

However, below freezing the sling psychrometer no longer give correct results as the heat of fusion of water will stop it from reading below freezing until the water is frozen at which point evaporation no longer occurs. It for this reason that wind chill cannot make liquid water colder than ambient when the temperature is below freezing. In fact, wind chill cannot bring the temperature of pure water below the triple point of 32F (0C) until all of it is frozen. For a brine solution the relevant temperature will depend on the brine concentration.

Once the solution is frozen the wind only serves to reduce the temperature of the ice to ambient faster and cannot make it colder than ambient since no evaporation occurs (ignoring the very small effect of sublimation).

The situation for water vapor (gas form) is much more complex as water can remain in gas form down to about -40 degrees.

Carl
02-27-2006, 12:40 PM
Since airflow across an inanimate object has no effect, I think I will throw away my car's radiator fan and mount the radiator in a less conspicuous place.

http://img.photobucket.com/albums/v35/lathefan/296aa9fb.gif

jburstein
02-27-2006, 12:44 PM
Totally different effect Carl. That's convection heat transfer, not phase change heat transfer.

-Justin

lynnl
02-27-2006, 12:45 PM
"(ignoring the very small effect of sublimation)."

It's no 'small effect'. That will involve the same latent heat as melting Plus evaporation. (Maybe not exactly, but close)

But your last post made me realize I've forgotten how the weather observer's sling psychrometer procedure varied for sub-freezing conditions, or if it did at all.

I kinda think the procedure used was the same, and the differences were accounted for within the calculator used.

Evan
02-27-2006, 12:52 PM
"It's no 'small effect'. That will involve the same latent heat as melting Plus evaporation. (Maybe not exactly, but close)"

The heat involved is indeed the same as the latent heat of condensation plus the latent heat of fusion (crystallization) or about 680 calories per gram. However, it proceeds at a very low rate so the contribution to cooling is negligible.

cam m
02-27-2006, 01:10 PM
Sorry I can't let this one go by. See here for windchill calc. http://www.eol.ucar.edu/homes/rilling/wc_formula.html
Windchill is a comparison between convective ( wind) and conductive ( still air) heat transfer and is independent of humidity or evaporative effects. 15 F and 20 mph wind "feels like" -2 F because the heat loss from exposed skin is similar to still air conditions at -2 F. Physics professor and supporters obviously do not understand windchill as calculated or defined.

[This message has been edited by cam m (edited 02-27-2006).]

Evan
02-27-2006, 01:13 PM
I'm speaking about the potential cooling effect of wind on water as suggested above on a roadway, not people or even other objects. Water has anomalous chacteristics that make such considerations different than for other materials.

cam m
02-27-2006, 01:19 PM
Admittedly evaporative effects compound the heat loss. That is why damp skin loses heat faster than dry skin. BUT THAT IS NOT WINDCHILL.

Evan
02-27-2006, 02:24 PM
No it's not. I wasn't talking about windchiil as commonly used to describe the effect of wind on people.

debequem
02-27-2006, 02:37 PM
So, how does one feel cool when the ambient temperature is high (80 - 90 degrees F)and there is a breeze? Evaporation of perspiration is the main reason. Check the charts (depends on which standard you apply), but it is possible to have wind chill effects at high ambient temperature, so the mechanism is not simply cool convective air.


<font face="Verdana, Arial" size="2">Originally posted by cam m:
Sorry I can't let this one go by. See here for windchill calc. http://www.eol.ucar.edu/homes/rilling/wc_formula.html
Windchill is a comparison between convective ( wind) and conductive ( still air) heat transfer and is independent of humidity or evaporative effects. 15 F and 20 mph wind "feels like" -2 F because the heat loss from exposed skin is similar to still air conditions at -2 F. Physics professor and supporters obviously do not understand windchill as calculated or defined.

[This message has been edited by cam m (edited 02-27-2006).]</font>

Evan
02-27-2006, 02:41 PM
On the subject of windchill as it applies to people it is basically a meaningless number anyway. It has no relevance to how fast you cool down unless you are in the habit of streaking at 30 below zero. I speak from experience (not streaking!) having been out and working in temps as low as -50. In those conditions your main heat loss comes from breathing.

lynnl
02-27-2006, 03:12 PM
I wouldn't call it a totally meaningless number. Used qualitatively it can be somewhat meaningful. But it certainly has been oversold, or I should say overbought.

I hear the TV weather shows here in Nth Ala speaking of a wind chill of 23d F (Brrr!!) when we have 30d temp and 6 or 7kt winds, or whatever. Gimme a break!
Of course around here anything below about 20-25F is termed "brutally cold!" (literally, ..and with a straight face) http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif

I think the USAF charts only broke it down in increments of 5 or maybe even 10 degrees.
We were often asked for the formulas, and the answer (USAF) was that there are no formulas. It was an emperically developed chart to guide manpower management of outside activities, exposure time limits, etc..

cam m
02-27-2006, 03:18 PM
Windchill is defined as above and is not a comprehensive catch-all for cooling. Cooling effects INCLUDE wind action by convection AND evaporative effects. Evaporative cooling is the mechanism swamp coolers work by. Its all about semantics - the right name for the right thing. Incidentally, there is a point where one effect will be more dominant than another. At warmer temperatures, evaporative cooling dominates over the convective effects and vice versa. The convective effects are more dominant where the temperature differentials are higher.

Lynnl - there are calculations. Those airforce tables came from somewhere. The formula is in the link as well as a quick explanation of both methods of analysis.



[This message has been edited by cam m (edited 02-27-2006).]

Evan
02-27-2006, 03:35 PM
But, those calculations are nonsense. I have often heard statements related to windchill factor saying something along the line that "exposed skin will freeze in two minutes" and so on. Bull. I have spent hours outside doing astrophotography at night in -20 and have never frozen my face or hands even though exposed for much of the time.

It just doesn't work as advertised. Even at -40 skin doesn't freeze in two minutes. I've been out plenty of times at those temps. It is cold and my beard will frost up but I still have all of my nose.

Allan Dimmock
02-27-2006, 03:58 PM
I used to ride in winter much more often than I do now. I remember on one occasion watching a little puddle of water on the petrol tank as it froze and thawed as I rode along. The puddle would freeze when I went fast and thaw when I went slow. I guess the puddle could have been getting smaller, but it wasn’t obvious. From bitter experience, I know that if I ride fast, I get colder quicker than if I ride slow. I’ve always attributed that to "wind chill".

The reason I always thought that wind chill was a factor in the formation of black ice is due to a mishap I had one winter. I was just about home after riding back from work, but as I went to turn right I dropped the bike as it hit a patch of black ice. The rest of the road was covered in mixture of compacted snow and slush, but this patch was on a small rise and the snow had cleared during the day, making the surface look "safe" compared with the rest of the road. There was a steady (and cold, straight from Russia) east wind blowing across this cross roads, so I assumed that this had dropped the road temperature below that required to freeze the surface water. That piece of road had previously been warm enough to melt the snow, so something must have cooled it down. Whether or not evaporation was responsible, the net result was the same.

That mishap was an interesting experience. There was another motorcyclist behind me when I fell off. Being a nice sort, he tried to stop to help me, but of course he hit the ice. As he fell off, the car following him jammed on the anchors, and that car hits the guy who has fallen off, pinning him between his bike and the car. No ABS in those days. To add to the fun, the car following that car hit the brakes and started sliding. This car hit the first car, which was still sliding along, pushing the bike, with the rider still pinned between. I was sat on my arse in the middle of the road, watching this whole ensemble, two cars, one man and one motorcycle, coming towards me. The train came to a halt a couple of yards away from me, with no damage to either of the cars, the biker or motorbike. Fascinating to watch, but not from the middle of the road.

lynnl
02-27-2006, 03:59 PM
I think the military developed the concept and tables first, then other researchers tweeked and twiddled and worked up formulas to fit.

(added)
Allan, there are several factors that can interact. If the sun has been shining on the road surface during the day, and heating it up, then certainly increased airflow over the surface will serve to dissipate that heat and cool the roadway surface quicker. Then if there's sufficient humidity in the air, it starts depositing rime ice (frost) onto the subfreezing, dry surface thru the sublimation process. The result, we call black ice.

Or, if the ground has been relatively warm (above freezing) for a few days before, and is very moist, then a cold front drops the air temp substantially below freezing. ...After a few hours as the upper thin layer of ground and road surfaces drop below freezing then the moisture (water vapor) escaping from the ground can start sublimating and depositing rime ice on the surface. Result - Black ice.

(added again)
Oh, one other significant factor, that I forgot to mention, is radiational cooling that becomes more pronounced at nightime, and more so for dark objects (or what's known as a 'black body'). Surfaces, that are initially at thermal equilibrium with the ambient air will lose heat thru radiation into space, so they become colder than the air, enhancing frost formation on an otherwise dry surface.

Oddly enough, snow, which appears white to us, actually is a near perfect 'black body' at nighttime. Meaning it radiates heat into space very effectively.
[This message has been edited by lynnl (edited 02-27-2006).]

[This message has been edited by lynnl (edited 02-27-2006).]

cam m
02-27-2006, 04:35 PM
Semantics police again... Sublimation is vaporization directly from the frozen solid as in "dry ice" not a phase change from gaseous to liquid or solid. The process Lynnl describes is condensation and freezing. Black ice is black because it is clear. It forms as Lynnl says from condensation, melt water or new precipitation. To form black ice, the liquid water forms a continuous film which then freezes in a clear, transparent layer that appears darker because the surface it froze on was wet and because the layer of ice does not reflect headlights the same as dry surfaces. Other ice is opaque and white because of air bubbles, contaminants, or being made from compacted snow, etc. Or it froze before the mini droplets of water had a chance to flow together before freezing.



[This message has been edited by cam m (edited 02-27-2006).]

lynnl
02-27-2006, 04:44 PM
The term 'sublimation' applies to either direction: ice to vapor, or vapor to ice.
It's sublime, in that it skips the middle energy state.

Evan
02-27-2006, 05:06 PM
While technically sublimation does mean phase change in either direction the change from vapor to solid is now usually refered to as "deposition" so there is no confusion.

Your Old Dog
02-27-2006, 08:56 PM
<font face="Verdana, Arial" size="2">Originally posted by spope14:
Fuel shut off, yes. I set mine off when I got "curbed" by a person who cut me off in traffic. The curbs here are granite, 6 inch high straight up things, thus the impact shut me off ASAP (Ford Ranger) and the front wheels were also bent.</font>

One of my more embarrassing moments in life. Pulling thru a toll booth, fumbling for change I kissed the razor sharp granite curb with my 70's era wide oval tires at 28 lbs pressure. The tire immediatley went flat from the resultant cut and I had to wop wop wop my way to the window, pay the lady, and then wop wop wop my over to the side of the road http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif

Evan
02-28-2006, 01:44 AM
"Oddly enough, snow, which appears white to us, actually is a near perfect 'black body' at nighttime. Meaning it radiates heat into space very effectively"

The reason for that is because water in all phases while transparent to visible light is opaque to infrared. So, as per Kirchhoff's Law a good absorber is an equally good emitter of the same wavelength of energy.

Incidentally, the principle of the night sky radiative cooling effect has been used for millenia to make ice. The ancient arabs used this effect in the desert to make ice by building a low thick stone wall that shielded water placed behind it from the southern sky and any other objects nearby. The stone wall itself was never exposed to sun on the north side so it didn't absorb much heat. It is possible to freeze water this way even if the air temperature is above freezing. The temperature of space is about three degrees kelvin or just about absolute zero. With the heat radiated by the atmosphere on a very clear night the effective temperature of the night sky as seen from the ground is about -70C.

alrednek
02-28-2006, 06:16 AM
I stand by what my uncle told me years ago about wind chill. In laboratory conditions by applying vacuum, using various chemicals in solution or in non-natural situations there might be possibile exceptions. I was only stating the science concerning wind chill in a natural sense. The discussion we were having when he enlightened me was about whether plain water in a car's radiator can freeze if the temperature is 33 degrees F and you are traveling at 55 mph. Now obviously this would be in "real world" conditions, not laboratory conditions. He said that it was not possible and explained the wind chill theory to me. I am convinced now that he is correct, and so are quite a few others (I borrowed these links from Cynthia_ga on Google):

National Science Digital Library - An Introduction to Wind Chill
http://avc.comm.nsdlib.org/cgi-bin/wiki.pl?An_Introduction_To_Wind_Chill
(bottom of the second paragraph)
..."If the air temperature is 40 degrees F and the Wind Chill Factor
is 10 F degrees, water will not freeze..."


Wind Chill Information
http://media.mgbg.com/wrbl/images/weather/weatherwise/wind_chill.html
..."Does that mean wind chill can freeze things? No, wind chill cannot
freeze things, only the outdoor temperature can do that. No matter how
hard the wind blows, the temperature does not change. But wind does
make things cool off faster. For example, some people believe water
will freeze when the wind chill dips below freezing. But that isn’t
the case. Water will freeze only when the actual temperature dips
below freezing. But wind will help water freeze faster by removing
heat from the water, so wrap insulation around your exposed
pipes......[this was very interesting:]...There is little danger of
wind chill hurting you in our area because it’s tough to get frostbite
with windchills warmer than -20F. But if wind chills go below -70F,
skin will freeze in seconds..."


Wind chills won't freeze water
http://www.wonderquest.com/wind-chill.htm
..."Q: If the ambient temperature is 35° F with a wind chill factor of
25° F, will water [NOAA] Rochester, Minnesota blizzard in March
1966.freeze? I say no, my friend says yes. How can we test this during
this time of the year?

A: You’re right. A wind-chill factor of 25° F (- 4° C) will not freeze
water if the air temperature is 35° F (2° C).

How to test this during the summer? Tough. Your best bet is to rig up
a refrigerator with a 15 mph fan. It takes a 15 mph (24 kph) wind to
produce a wind chill factor of 25° F if the air temperature is 35° F.
..."

NOTE: The page above has a link to this experiment:

Wind-chill experiment
http://www.wonderquest.com/wind-chill-experiment.htm


Engineere Edge: Wind Chill Equation and Calculator
http://www.engineersedge.com/calculators/wind_chill.htm
..."Wind Chill temperature only will not cause water to freeze. Water
will only freeze when the waters temperature reaches the freezing
point..."


From USA Today:

Answers archive: Can wind chill alone freeze water
http://www.usatoday.com/weather/resources/askjack/2002-12-01-answers-wind-chill_x.htm
..."Q: If the temperature is 38 degrees and the wind chill is 27
degrees, will water on roads freeze?

A: No. Wind chill attempts to account for the effects of wind carrying
heat away from your body, or the body of an animal. No matter how hard
the wind blows, it doesn't change the air's temperature. You find more
on this by going to a USATODAY.com file about Wind chill applies only
to people, animals..."

The most FAQ about wind chill
http://www.shorstmeyer.com/wxfaqs/windchill/windchill.html
..."If the air temperature is 35 deg. F. and the wind chill 20 deg.
F., will water freeze?

No! Wind Chill expresses how quickly you will lose body heat. At 20
deg. F. and 20 mph, the wind chill is -10 deg. F. The index (-10 deg.
F.) is the equivalent temperature telling you that your body loses
heat as fast as if the temperature is -10 deg. F. and the wind light.

How cold a glass of water can get is dictated by the second law of
thermodynamics which says the water cannot freeze until the
temperature hits freezing, that is it can only cool to whatever the
air temperature is. The wind chill will just get it there faster..."

Please Pass the Science by dr. scott berk
http://www.cardhouse.com/berk/science96.htm

This link has technical information that mathmatically proves wind
chill won't freeze water:
http://avc.comm.nsdlib.org/cgi-bin/wiki_grade_interface.pl?An_Introduction_To_Wind_Ch ill

This is interesting:

Brainstorm Answer: Freezing Water
http://www.weathernotebook.org/transcripts/1999/02/12.html

Sorry for the long post.

Mike