Why does wet cold air feel so much colder than dry cold air?

[lemur]

What about the effect of water vapor freezing below 0C? I would think that as water vapor freezes, it collects into crystals, thus decreasing the total number of water particles and their ability to spread out when they come in contact with skin and clothing. I realize that surface tension in liquid water would also have the effect of reducing the number of particles, but I don't think that surface tension is a factor in vaporized water. Is crystallization a factor when the water freezes? Also, does dry frozen water have the same ability to absorb heat as dampness in/on air, clothes, and/or skin?

Edited January 13, 2011 by lemur

[Moontanman]

What about the effect of water vapor freezing below 0C? I would think that as water vapor freezes, it collects into crystals, thus decreasing the total number of water particles and their ability to spread out when they come in contact with skin and clothing. I realize that surface tension in liquid water would also have the effect of reducing the number of particles, but I don't think that surface tension is a factor in vaporized water. Is crystallization a factor when the water freezes? Also, does dry frozen water have the same ability to absorb heat as dampness in/on air, clothes, and/or skin?

 

 

I think it was mentioned earlier that generally when it's cold and the humidity is very high it is often cloudy which helps prevents sharp temperature drops. I've seen ice condense directly out of the air twice in 40 years of living near the ocean and seeing cold wet air. interestingly enough both times it was a clear sky and wet air that allowed this to happen, radiative cooling under clear skies allowed the moisture to condense directly into ice while I was fishing, everything became covered in ice over a few minutes as the temps fell.

[alpha2cen]

Heat transfer rate depends on temperature gradient and heat transfer coefficient.

If temperature gradient is same, the transfer rate depend on the heat transfer coefficient.

In the moving air condition heat transfer rate highly dependent on heat transfer coefficient by moving air.

But in the stationary air condition, we do not neglect surround air heat capacity, because it varies temperature gradient.

And, we do not neglect natural convection surround us, too.

Heat capacity, heat transfer coefficient and thermal expansion coefficient are related to nature convection phenomena.

So in the humid stationary air condition, the high heat transfer rate, I suppose, is caused by high heat capacity and increased thermal conductivity on the more wetter skin surface.

[lemur]

I wish I had the quantitative skills to compare the rate of heat transfer from an object at 36C to three different heat sinks: 1) +2C air at 90% relative humidity 2) - 2C air at 90% relative humidity and 3) -2C air at 10% relative humidity. I don't even know what unit the results would come out as, joules/second?

Edited January 14, 2011 by lemur

[alpha2cen]

Heat transfer rate[J/s]=(Total heat transfer coefficient[J/m^2.s.oC]) x (Heat transfer area[m^2]) x (Temperature difference[oC])

In this problem we consider all problem's heat transfer area are same, temperature difference are same, too.

Total heat transfer coefficient term is consists of natural convection + radiation+ conduction.

Air conductivity is very law. So convection transfer and some of radiation transfer are important role on this system.

And, on the calculation of the convection, total heat transfer coefficient contains the term of surface material conductivity .

Edited January 15, 2011 by alpha2cen

[PaulSpring]

Intuitively the conductivity explanation sounds more credible. Also, my experience is that cold damp air doesn't immediately feel colder than cold dry air. The difference is that, over time, it feels like it leeches the warmth out of you quicker, which would make sense if it was conducting heat away faster.

 

Moontanman, you said "I've seen ice condense directly out of the air twice in 40 years of living near the ocean and seeing cold wet air". Where I come from in East Anglia, this phenomenon happens at least half a dozen times every winter. It's called hoar frost.

Edited December 4, 2012 by PaulSpring

[alpha2cen]

This is a cause of heat transfer increasing.

Convection is main cause of heat transfer at that temperature range.

Convection heat transfer coefficient is related to the convection layer thermal conductivity and others.

 

Edited December 4, 2012 by alpha2cen

[Moontanman]

Intuitively the conductivity explanation sounds more credible. Also, my experience is that cold damp air doesn't immediately feel colder than cold dry air. The difference is that, over time, it feels like it leeches the warmth out of you quicker, which would make sense if it was conducting heat away faster.

 

Moontanman, you said "I've seen ice condense directly out of the air twice in 40 years of living near the ocean and seeing cold wet air". Where I come from in East Anglia, this phenomenon happens at least half a dozen times every winter. It's called hoar frost.

 

 

Here the water condenses as a layer of thin transparent ice not frost, but it does frost here as well...

[galileo81]

I have to go with John Cuthber on thermal conductivity and am offering my theory on this.

 

I don't believe it can be explained by heat capacity alone because air has less than 1% water vapour - so the impact by itself would be difficult to detect.

 

Dry air is comprised of oxygen and nitrogen which have no dipole, whereas water has a dipole.

 

The human body is 80% water and the micro-climate in the lungs is highly humid as well as the skin surface.

 

Dry air cannot "stick" to the surface because if I recall chemistry - non-polar molecules are insoluble in water but polar molecules dissolve in water.

 

Dry air being comprised of symmetrical gases will therefore not stick to the skin or the lungs.

 

But wet air will stick to the skin - this act of sticking results in substantially greater thermal conductivity. Probably several times as much.

 

That's why people use words like "the damp gets into your bones" - as it tends to cling to the body.

[Rajnish Kaushik]

the answer is simple

the water molecule add extra colling effect

[knyazik]

Why would it be a contradiction?

It's true and it doesn't sound like a contradiction to me.

 

What still puzzles me however is how 1% water in air can have such an influence.

That is peculiar, but you can always think about it from another point of view. Suppose you were drinking tea and 1 % of it was crude oil. I'm sure you would notice the difference, lol! As Einstein always said everything is relative (silly joke out of theory of relativity).

[J.C.MacSwell]

From my experience in cold weather, dry cold air seems to keep my insulation (clothing) dryer, and damp cold air otherwise. I think this has a significant effete on the insulation value.

If, say, I put on a cold but dry light down vest, it quickly seems to add warmth, where as the same vest put on damp, even if taken from inside a warm house, seems to have less effect. Evaporation cooling may be part of it, but I think the insulation value is compromised as well.