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Old 11-30-2007, 09:08 AM   #1
bsmeaton
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Wind Chill

Hmmmmmm - just having a little discussion with my son about wind chill and we were trying to figure -

Does wind chill affect inanimate objects? I'm assuming no? just because a thermometer can't read it?
 
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Old 11-30-2007, 09:19 AM   #2
bncinwv
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Brad,
You are correct, wind chill is only a function of the body, if it was otherwise, our temperature guages in vehicles travelling 60 mph at 32 degrees F would be reading negative temperatures. Wind chill is a measure of the apparent temperature that we feel when the wind is blowing, surprised you didn't do some web research on it???
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Old 11-30-2007, 09:29 AM   #3
firetrucker
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Brad, as it turns out, wind chill does affect inanimate objects. In fact, the first wind chill measurements were made in the Antarctic before WWII by hanging a small plastic bottle filled with water at the same height as the anemometer and measuring how fast the water froze.

To quote Wikipedia (an excellent source): Right at the surface of the skin, the adhering air is still. Because air has some internal stickiness (viscosity), there is drag between the adhering air and the air molecules farther away from the skin. As a result, near the skin or any surface there is a zone of relatively still air that may be several millimetres thick. This is the boundary layer.

The insulation of the boundary layer depends on its thickness. When there is wind, the thermal resistance of the boundary layer is smaller, the heat loss is higher and the temperature of the skin is closer to the air temperature. Humans do not sense the temperature of the air. When we feel that it is cold outside, we are actually sensing the temperature of our skin. Because our skin temperature is closer to the air temperature when it is windy, we feel that the wind makes it colder outside. That is the essence of wind chill.

How's that?

Bob
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Old 11-30-2007, 09:35 AM   #4
bncinwv
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As a follow up:

By definition, Wind Chill Temperature is the temperature that it feels like. It is based on the rate of heat loss from exposed skin caused by combined effects of wind and cold. Without wind, the air next to skin warms by contact (conduction) and provides an invisible blanket around the skin. As the wind speed increases, this protective layer of heated air is carried away from the body at an accelerated rate. With heat loss from the skin, the body must either generate more heat or itself cool down.

According to the new NWS Wind Chill Chart, if the temperature is 0 degrees Fahrenheit and the wind is blowing at 15 mph, the wind chill is -19 degrees Fahrenheit. This means that without any wind (actually a 3 mph wind or a 3 mph walking rate), the rate of heat loss would equal that of outside air at -19 degrees Fahrenheit. At this wind chill temperature, exposed skin can freeze in 30 minutes. For other conditions of wind and temperature, check out the new NWS Wind Chill Chart and Calculator.

So much for the chilling effects of wind and cold temperatures on human skin. What about the effect of wind chill on things like car radiators or exposed water pipes?

Because wind chill is based on removing heat from the human body, there is no wind chill for inanimate objects, such as car radiators and water pipes. However, there is a faster heat loss with increasing winds, so the amount of time for an object to cool to the actual air temperature is less. Regardless, the inanimate object cannot not cool below the actual air temperature. Thus, if the temperature outside is -5 degrees Fahrenheit and the wind chill temperature is -31 degrees Fahrenheit, then your car's radiator will not drop lower than -5 degrees Fahrenheit.

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Old 11-30-2007, 09:39 AM   #5
stiles watson
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So does that mean that at 32 degrees water freezes faster if it is windy?
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Old 11-30-2007, 09:54 AM   #6
bncinwv
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Yes, because the water is cooling faster. If the water is at 40 degrees it will get to 32 degrees faster, it will not freeze any faster once it reaches 32 degrees. Clear as mud????
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Old 11-30-2007, 09:59 AM   #7
firetrucker
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Yes, water will freeze faster, and your body will not get colder than -5 degree F no matter what the wind chill is if the temperature is -5 degrees F ambient. The key is what you feel like it is compared to a no wind condition.

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Old 11-30-2007, 10:03 AM   #8
bsmeaton
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Quote:
quote:Originally posted by bncinwv

surprised you didn't do some web research on it???
Bingo
Bingo - If I search on the web I just get lies and more lies - here I can get the truth!

Firetrucker, it seems if water is involved, especially evaporating, it is impacted. Maybe even a pipe, radiator, - or "fire hose?". If I understand it correctly??
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Old 11-30-2007, 10:30 AM   #9
firetrucker
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If something's warmer than ambient, it will see an effect of the wind. If it's the same temperature as ambient, then there will be no effect. Evaporation takes a lot of energy out of a fluid, so that would compound the effect. The effect will work in reverse, too. If you want to warm something up, disturb that insulating layer with moving air and it will warm faster.

And, yes, never shut down a fire hose when it's below freezing. Because of their construction, old structure hoses weeped, but now hoses are designed to hold pressures up to about 400 psi. We have to test all our structure and supply hoses every year to 300 psi.

Bob
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Old 11-30-2007, 11:19 AM   #10
Ozzie
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I like firetrucker's response...

When I was younger, my boss used to tell us wind chill only mattered if you were naked and standing up on a roof.
...of course he wanted us to work, so convincing us it wasn't that cold out was part of his program.
Having worked outside in winter weather most of my years, I can see the effects of the wind on anything that has some heat. It only stands to reason that anything will loose it's heat faster in the wind simply because the cushion (or buffer) of air around that object is being depleted by the wind.
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Old 11-30-2007, 11:50 AM   #11
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Having to fight several winter structure fires on the Wisconsin/ Michigan line in February I can ascertain the effect on minus numbers on hoses. As soon as the hoses are wet on the outside be it from seepage on older style hose or with the newer HiCombat hoses from spray, everything thing sticks to the ground at -28. Even boots if you stand in the same place holding a hose for a few minutes. The 40 knot wind didn't help any part of fighting that fire either. I was kneeling in a puddle for half an hour and had trouble getting back up because my cuff and boot sides were frozen to the driveway.. Thats why I now spend winter in warmer climes... Dave and Betsy
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Old 11-30-2007, 01:20 PM   #12
The Oldguard
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Then why is it colder inside an empty building that has no heat, than it is outside no matter what the temperature or the wind speed is outside
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Old 11-30-2007, 03:39 PM   #13
bncinwv
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Not to cause an argument, but rather for informing others, Wikipedia should not be considered as a reliable reference source. High School and College students will be subject to criticism if they use Wikipedia as a source for reference papers. The information on Wikipedia can be posted and amended by anyone who submits without verfification of it's authenticity, it should be treated as the hearsay that it is. Don't get me wrong Wikipedia can be used for information but it should not be used as a reliable reference without verifying the info.
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Old 11-30-2007, 08:12 PM   #14
firetrucker
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Bill, if things are in equilibium, it will not be colder, or warmer, inside no matter what the temperature outside or the wind speed. I think it will FEEL colder because there are six surfaces that are absorbing more heat from our bodies than they are radiating. I suspect that if the temperature of the building is above our body temperature, we will feel warmer than it really is.

Bingo, you're right about Wikipedia being a questionable resource, especially with new articles...a fact they readily admit and caution users about. But they do have an extensive review policy that more often results in much increased reliability with time that rivals almost any reference work. Any student that tries to put something over on their teacher (or themselves) by using a single reference, especially material off the Internet, deserves the grade they SHOULD (but too often don't) get. After having taught for about 20 years, my BP tends to rise dramatically when I see how we're not living up to our resonsibilities to teach, and to learn, effectively and efficiently, whether we're a parent, teacher, or student!

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