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tommac
2010-Mar-01, 03:12 PM
How does a sauna work when you add water to the rocks? What i thought happened was that the water turned to steam and heated up the sauna. However I was just in a discussion with someone and they said that it actually cools down the sauna but it feels hotter because there is more humidity. I guess I am assuming that the steam is boiling water so how could that cool down the sauna?

jokergirl
2010-Mar-01, 03:24 PM
Some of the heat energy in the sauna goes to heat the water, I would say.

Ara Pacis
2010-Mar-01, 03:36 PM
Hot rocks radiate energy. Putting water on them will cool them down but carry more heat into the air via advection, IIRC. It would cool down the rocks but heat up the sauna, if you think of the sauna as the air inside of it. If you think of the sauna as a system as a whole, then the water in the bucket was already in the sauna and its "coolness" was already there, so you're not actualy changing the heat in the system, just moving it around. If you import water into the system, via an external tap or new bucket, then maybe you are reducing the heat in the system as a whole, but you may not notice it right away.

hhEb09'1
2010-Mar-01, 03:52 PM
Since the door is closed, we don't lose that much energy, right? :)

The rocks are cooled when they heat the water, which heats up the air as it becomes water vapor, right? You lose some of the radiative heat, so the air starts to cool a little.

What was the question again?

Strange
2010-Mar-01, 04:01 PM
Since the door is closed, we don't lose that much energy, right? :)

But that doesn't mean the temperature doesn't change - some the heat will go into the water's change of state (latent heat of vaporization? it's a long time since I had to think about stuff like that). But I suspect the change in humidity and apparent temperature is more significant.

The humidity will make you sweat more which is why you feel hotter and is, I suppose, considered a "good thing".

ETA: all right, all right, I know, I didn't say that right. Leave me alone.

rommel543
2010-Mar-01, 04:38 PM
The heat from the rocks is transfered into the water creating steam. The water hold the heat better than the air and thus maintaining the heat the in room longer. Also with the increased humidity, the radiant heat from the rocks is transfered easier.

JohnD
2010-Mar-01, 06:50 PM
The heat in the rocks, goes to water vapour, to your body. It's a form of convection.

That water vapour condenses on your skin. As it does so, it gives up the heat of vapourisation to your body, so you gain heat. It's the reverse of sweating!

John

PetersCreek
2010-Mar-01, 07:35 PM
The humidity will make you sweat more which is why you feel hotter and is, I suppose, considered a "good thing".

Humidity makes you sweat more? With RH at or approaching 100%, I think greatly reduced evaporative cooling is the biggest reason you feel hotter. That's one of the reasons I don't live in the Deep South anymore!

cran
2010-Mar-01, 07:52 PM
How does a sauna work when you add water to the rocks? What i thought happened was that the water turned to steam and heated up the sauna. However I was just in a discussion with someone and they said that it actually cools down the sauna but it feels hotter because there is more humidity. I guess I am assuming that the steam is boiling water so how could that cool down the sauna?
"someone" was half right - it feels hotter because there is more humidity ...
raising the humidity or moisture content in the air retards the evaporation of sweat from your skin - it's the evaporation that causes the "cool" feeling (by drawing heat from your skin) - so, you still sweat, but the sweat can't evaporate as quickly if the air is already saturated, and therefore your skin is not losing heat as fast, and you feel hotter ...

Strange
2010-Mar-01, 08:18 PM
Humidity makes you sweat more? With RH at or approaching 100%, I think greatly reduced evaporative cooling is the biggest reason you feel hotter. That's one of the reasons I don't live in the Deep South anymore!

Uh. Yeah. Right. Exactly. Thats what I said. Or meant to say. Or was thinking. Honest. Blame the heat...

LotusExcelle
2010-Mar-01, 08:38 PM
Can I relate my first sauna experience? It was in Finland and far north of the arctic circle. Anyway - the interesting part was that my eyeballs fogged up for several minutes. You can't imagine how odd a feeling it is.

TheHalcyonYear
2010-Mar-01, 10:32 PM
The humidity will make you sweat more which is why you feel hotter and is, I suppose, considered a "good thing".
Uh, no. One just sees the sweat accumulate on one's skin because it does not evaporate off the skin when the surrounding air is already is already saturated with water vapor.

Strange
2010-Mar-01, 10:41 PM
Uh, no. One just sees the sweat accumulate on one's skin because it does not evaporate off the skin when the surrounding air is already is already saturated with water vapor.

I know, I know. :wall:

Ara Pacis
2010-Mar-01, 11:39 PM
Uh, no. One just sees the sweat accumulate on one's skin because it does not evaporate off the skin when the surrounding air is already is already saturated with water vapor.

For some reason I seem to remember hearing or reading that the sweat, or rather the water component of perspiration, might evaporate, but is replaced by water condensing at the same or faster rate.

TheHalcyonYear
2010-Mar-01, 11:52 PM
For some reason I seem to remember hearing or reading that the sweat, or rather the water component of perspiration, might evaporate, but is replaced by water condensing at the same or faster rate.
hmmmm, I'm wondering why the water oozing from one's pores would be preferentially taken into the air over the water that is already there. Since the sauna is heated to around body temperature already, there should be no gradient and it would seem that the only exchange would be the equilibrium exchange (much like the equilibrium point in a chemical reaction.)

Ara Pacis
2010-Mar-02, 12:36 AM
hmmmm, I'm wondering why the water oozing from one's pores would be preferentially taken into the air over the water that is already there. Since the sauna is heated to around body temperature already, there should be no gradient and it would seem that the only exchange would be the equilibrium exchange (much like the equilibrium point in a chemical reaction.)

That's my point, there may be no preferential direction, hence molecules move in both directions.

cran
2010-Mar-02, 03:55 AM
hmmmm, I'm wondering why the water oozing from one's pores would be preferentially taken into the air over the water that is already there. Since the sauna is heated to around body temperature already, there should be no gradient and it would seem that the only exchange would be the equilibrium exchange (much like the equilibrium point in a chemical reaction.)

sauna temperatures are usually higher than body temperature ...
a cool humid sauna is a minimum 40 degC
warm humid to hot dry saunas range from 60-90 degC

HenrikOlsen
2010-Mar-02, 07:05 AM
Since the sauna is heated to around body temperature already, ...
If your body temperature is 200F you should see a doctor.
Yes, some saunas do go that high.

PetersCreek
2010-Mar-02, 07:41 AM
If your body temperature reaches 200F, please seek emergency mortuary treatment immediately!

hhEb09'1
2010-Mar-02, 04:36 PM
For some reason I seem to remember hearing or reading that the sweat, or rather the water component of perspiration, might evaporate, but is replaced by water condensing at the same or faster rate.I think that TheHalcyonYear's point is that is true of all systems--even one's not at equilibrium, there is a certain amount going in and a certain amount going out.
If your body temperature reaches 200F, please seek emergency mortuary treatment immediately!Just so you don't wait too long, I'd recommend initiating the call at 110F

cran
2010-Mar-02, 07:28 PM
by the way, don't let the high air temperatures scare you too much into thinking you'd be scalded just by sitting in the sauna room ...

because it takes even more energy to heat steam than it does to heat water, the water vapor (the re-condensed mist we commonly call "steam") does tend to be cooler than the air, but still warmer than your body ...

tommac
2010-Mar-05, 05:47 PM
Yeah this is what I thought ... the water goes to steam and heats the air right?


Hot rocks radiate energy. Putting water on them will cool them down but carry more heat into the air via advection, IIRC. It would cool down the rocks but heat up the sauna, if you think of the sauna as the air inside of it. If you think of the sauna as a system as a whole, then the water in the bucket was already in the sauna and its "coolness" was already there, so you're not actualy changing the heat in the system, just moving it around. If you import water into the system, via an external tap or new bucket, then maybe you are reducing the heat in the system as a whole, but you may not notice it right away.

tommac
2010-Mar-05, 05:50 PM
Humidity makes you sweat more? With RH at or approaching 100%, I think greatly reduced evaporative cooling is the biggest reason you feel hotter. That's one of the reasons I don't live in the Deep South anymore!

Yes but my question is about the temp of the air. Is it hotter or cooler after the water is applied ... lets forget about humidty or feeling hotter. I just want to know if the air gets hotter or cooler.

tommac
2010-Mar-05, 05:51 PM
sauna temperatures are usually higher than body temperature ...
a cool humid sauna is a minimum 40 degC
warm humid to hot dry saunas range from 60-90 degC
I am talking a dry sauna at around 180F

tommac
2010-Mar-05, 05:55 PM
If your body temperature is 200F you should see a doctor.
Yes, some saunas do go that high.

I think I saw this guiness book of world record thing that had a sauna at 240 F or something ... the lady in there was literaly frying an egg.

HenrikOlsen
2010-Mar-05, 06:33 PM
I read somewhere about an antarctic club 300, which is those who've gone from a 200F sauna right outside to -100F air.

tommac
2010-Mar-05, 06:58 PM
I read somewhere about an antarctic club 300, which is those who've gone from a 200F sauna right outside to -100F air.
hah that is probably a shock ...

cran
2010-Mar-05, 08:27 PM
Yeah this is what I thought ... the water goes to steam and heats the air right?
No - it just raises the relative humidity ...

NB - the specific heat of water is much higher than that of rock -
ie, heat advecting from rock to water will lower the temperature of the rock
much more than it raises the temperature of the water -
the specific heat of steam is an order of magnitude higher again ...

the inverse of specific heat is thermal conductivity -

Thermal conductivity is the quantity of heat transmitted through a unit thickness in a direction normal to a surface of unit area, due to a unit temperature gradient under steady state conditions.


@25C unless otherwise specified

Water 0.58
Water, vapor (steam) 0.016(@125C)
Snow 0.05 - 0.25 (< 0oC)

Earth, dry 1.5
Quartz mineral 3
Rock, solid 2 - 7
Rock, porous volcanic (Tuff) 0.5 - 2.5
Sandstone 1.7
-http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

if the steam was hotter than 90C (194F), it would scald you*,
and it would need to be hotter than the air to heat the air -
that thing we call a law of thermodynamics - yes?

*like the poor Russians the other day, one of whom heated the plunge pool
to near boiling by mistake - cooked himself and another to death.

cran
2010-Mar-05, 09:02 PM
I think I saw this guiness book of world record thing that had a sauna at 240 F or something ... the lady in there was literaly frying an egg.

still shy of the record -

air temperatures of 140C (284F) have been recorded as "bearable" in saunas ...

but even that pales compared with USAF experiments of dry air endurance in 1960 - 204C (400F) naked;
and 260C (500F) for heavily clothed; duration times not given ...
(as at 1985 - Guinness Book of Records 1986)