Working out windchill factor

[zakelwe]

There are equations for working out windchill temps from the ambient temp in conjunction with the speed in mph or km/h of the air. This can be used for working out theoretically how cold a heatsink could go with the fan.

However, does anyone have the equation for converting cfm to mph for a fan of area X ?

I'll have to work it out on pencil and paper otherwise.

Regards

Andy

[KnightElite]

I know that in Canada, what they used to do for measuring windchill factor was just hang a 10 gallon water bottle, and measure how much faster it froze at different windspeeds.

I believe they have now updated their system, and they had volunteers from the army stand in a windtunnel, and they measured how fast the body cooled off at different windspeeds.

I'm not so sure the calculation will be so simple. Plus, you also have to keep in mind surface area calculations, which could become complicated.

[zakelwe]

Originally posted by KnightElite
I know that in Canada, what they used to do for measuring windchill factor was just hang a 10 gallon water bottle, and measure how much faster it froze at different windspeeds.

I believe they have now updated their system, and they had volunteers from the army stand in a windtunnel, and they measured how fast the body cooled off at different windspeeds.

I'm not so sure the calculation will be so simple. Plus, you also have to keep in mind surface area calculations, which could become complicated.

I think that last paragraph might be an understatement :) However, a circular fan it pushes out a "tube" of air at that cfm, so given that I should be able to work how fast that tube moves out from the fan and thus the speed. I'll work it out tonight.

Last time I did a big measurement was 15 years ago at college using a radio telescope to measure the temperature of the sun. The only problem was we had a BBC radio transmitter just down from the observatory which :banana::banana::banana::banana:ed all the measurements up. I got the sun to be -20C .. which is not even the right order of magnitude.

Regards

Andy

[sjohnson]

Windchill doesn't really apply to non-warm blooded things, it's a measure of the heat loss equivalent.

Meaning, a wind-chill calculation of 15c in a room with ambient of 20c does NOT mean you can cool the CPU any lower than 20c. 20c is 20c real temp. Wind chill temp is a risk-factor pseudo temp used to judge exposure of people to the elements, not object cooling.

[Oc2theSkY]

One thing you need to know is that wind chill does not effect inanimate objects the same way it effects a person. With a wind chill of say -10 a person will feel that cold. All it will do to an inanimate object is allow it to cool faster. The object will only cool to the ambient temp however. I know this is true. I work on airforce aircraft in North Dakota. We use temp charts to figure out pressures for things like tires, acumilators and what not. When this is done we use the ambient temp not the wind chill, because, once again, wind chill does not effect inanimate objects the same way is effects liveing objects.

[sinn]

Originally posted by Oc2theSkY
One thing you need to know is that wind chill does not effect inanimate objects the same way it effects a person. With a wind chill of say -10 a person will feel that cold. All it will do to an inanimate object is allow it to cool faster. The object will only cool to the ambient temp however. I know this is true. I work on airforce aircraft in North Dakota. We use temp charts to figure out pressures for things like tires, acumilators and what not. When this is done we use the ambient temp not the wind chill, because, once again, wind chill does not effect inanimate objects the same way is effects liveing objects.


thats a good fact to know, now it makes complete sense to me why you cannot cool below ambient with air

[zakelwe]

Thanks for the information guys .. that has saved me pencil and paer and I have also learnt something. Thinking back on it whenever my temp probe has been in a windstream from my fan it has not read less than ambient as far as I can remember !!!!

I don't have to pay a consultancy fee now do I ?

Regards

Andy

[KnightElite]

Yeah, that seemed obvious, so I didn't mention it in my post, lol :D.

You will never be able to cool below ambient, with anything less than a refrigeration unit of some sort. Heatsinks, fans, watercooling, etc... can only get you to ambient temperatures, no better.

[dqniel]

Cooler air "pulls" heat out of whatever is next to it (heatsink for example). This happens because the heat is trying to transfer from higher to lower "concentration." This is why you will never see lower than ambient air temps with air cooling, because heat would have to move from a lower density (like a heatsink below ambient temps) to a higher density (the ambient air warmer than the heatsink)

[cobray]

Yes, dqniel is correct. Heat transfers from the hot side to the cold side

[freecableguy]

uhhhhh....windchill is just a determination of how cold "it seems" in the wind....it has nothing to do with an actual decrease in the temperature of the air...there are 2 (major) things that determine the cooling ability of air:

1) the mass flow rate of the air
2) the temperature of the incoming air charge mass

-kjb