So, does sweat cool your body through evaporation, or conduction, or
probably both?

So If I am sweating and I want to use it the most efficient way to cool
myself, I shouldn't wipe it off?

--Falooley

Bob Falooley wrote:
> So, does sweat cool your body through evaporation, or conduction, or
> probably both?
>
> So If I am sweating and I want to use it the most efficient way to cool
> myself, I shouldn't wipe it off?
>
> --Falooley

Stand in front of a fan to increase vaporation.

--
spammage trappage: replace fishies_ with yahoo

Bob Falooley wrote:
> Ignoramus20725 wrote:
>
>
>>In article >, Bob Falooley wrote:
>>
>>>So, does sweat cool your body through evaporation, or conduction, or
>>>probably both?
>>
>>through evaporation.
>>
>>
>>>So If I am sweating and I want to use it the most efficient way to cool
>>>myself, I shouldn't wipe it off?
>>
>>You should use a fan...
>>
>>i
>
>
> That is what I thought, but this FFID at work told me he was sure that it
> was more through conduction, so when you wipe your sweat off you wil be
> cooler.
>
> --Falooley

Don't listen to 'fitness gurus' that are FFIDs.

--
spammage trappage: replace fishies_ with yahoo

Ignoramus20725 wrote:

> In article >, Bob Falooley wrote:
>> So, does sweat cool your body through evaporation, or conduction, or
>> probably both?
>
> through evaporation.
>
>> So If I am sweating and I want to use it the most efficient way to cool
>> myself, I shouldn't wipe it off?
>
> You should use a fan...
>
> i

That is what I thought, but this FFID at work told me he was sure that it
was more through conduction, so when you wipe your sweat off you wil be
cooler.

--Falooley

In ,
Ignoramus20725 > typed:
> In article >, Bob Falooley wrote:
>> Ignoramus20725 wrote:
>>
>>> In article >, Bob Falooley wrote:
>>>> So, does sweat cool your body through evaporation, or conduction,
>>>> or probably both?
>>>
>>> through evaporation.
>>>
>>>> So If I am sweating and I want to use it the most efficient way to
>>>> cool myself, I shouldn't wipe it off?
>>>
>>> You should use a fan...
>>>
>>> i
>>
>> That is what I thought, but this FFID at work told me he was sure
>> that it was more through conduction, so when you wipe your sweat off
>> you wil be cooler.
>>
>
> sounds like he did not study his physics...
>
> i

First Law of Thermodynamics is where FFID's start to get it wrong.
It's down hill from there.

August Pamplona
--
The waterfall in Java is not wet.
- omegazero2003 on m.f.w.

a.a. # 1811 apatriot #20 Eater of smut
The address in this message's 'From' field, in accordance with
individual.net's TOS, is real. However, almost all messages
reaching this address are deleted without human intervention.
In other words, if you e-mail me there, I will not receive your message.

To make sure that e-mail messages actually reach me,
make sure that my e-mail address is not hot.

Bob Falooley > wrote in message >...
> So, does sweat cool your body through evaporation, or conduction, or
> probably both?
>
> So If I am sweating and I want to use it the most efficient way to cool
> myself, I shouldn't wipe it off?

Evaporation: so you should stand in front of a fan to get cool. If
you're wanting to wipe the sweat off for comfort, it's fine, though -
you only need enough sweat to cover the skin, and you'll have that
very soon after wiping anyway.

Peter

On Mon, 09 Feb 2004 16:31:12 -0500, Bob Falooley >
wrote:

>Ignoramus20725 wrote:
>
>> In article >, Bob Falooley wrote:
>>> So, does sweat cool your body through evaporation, or conduction, or
>>> probably both?
>>
>> through evaporation.
>>
>>> So If I am sweating and I want to use it the most efficient way to cool
>>> myself, I shouldn't wipe it off?
>>
>> You should use a fan...
>>
>> i
>
>That is what I thought, but this FFID at work told me he was sure that it
>was more through conduction, so when you wipe your sweat off you wil be
>cooler.
>
>--Falooley

Conduction to what? Even though the specific heat of water is very
high, the thermal mass of the sweat is way too small to sink any large
amount of heat from your skin by itself. So, for the water to be
conducting heat from your skin, it must be conducting it to something
else with a large thermal mass and low thermal resistance. But,
besides your own skin, the sweat is only contacting the surrounding
air, an extremely poor thermal conductor with a low thermal mass. So,
there's simply no place for the heat to go, unless you'r leaning up
against a metal door the whole time with your sweaty body.
Evaporation is the answer.

- bc

"Bob Falooley" > wrote in message
...
> >> So If I am sweating and I want to use it the most efficient way to cool
> >> myself, I shouldn't wipe it off?
> >
> > You should use a fan...
> That is what I thought, but this FFID at work told me he was sure that it
> was more through conduction, so when you wipe your sweat off you wil be
> cooler.
>

OK, WTF is a FFID ?

Martin

--


=================================
anti-spam: replace breathof2dogs****ing with cooney to send me email
=================================

bc wrote:

> Conduction to what? Even though the specific heat of water is very
> high, the thermal mass of the sweat is way too small to sink any large
> amount of heat from your skin by itself. So, for the water to be
> conducting heat from your skin, it must be conducting it to something
> else with a large thermal mass and low thermal resistance. But,
> besides your own skin, the sweat is only contacting the surrounding
> air, an extremely poor thermal conductor with a low thermal mass. So,
> there's simply no place for the heat to go, unless you'r leaning up
> against a metal door the whole time with your sweaty body.
> Evaporation is the answer.
>
> - bc

FFID here, and that's almost exactly what I was saying to Falooley which
fomented this question in the first place. I'm saying the cooling effect
is from the conduction of the heat from your body to the sweat. The air is
a good insulator, so to remove the heat quickly you wipe away the sweat
since it takes a long time for it to evaporate, during which all that heat
energy is sitting on your skin. If you want to cool off don't wait for
evaporation, wipe off the sweat and you'll feel cooler faster.

Oh yeah, and if I can convince you stop ****ing calling me FFID...I'm not in
denial you mooks.

-FFNID

Bob Falooley wrote:
> bc wrote:
>
>
>>Conduction to what? Even though the specific heat of water is very
>>high, the thermal mass of the sweat is way too small to sink any large
>>amount of heat from your skin by itself. So, for the water to be
>>conducting heat from your skin, it must be conducting it to something
>>else with a large thermal mass and low thermal resistance. But,
>>besides your own skin, the sweat is only contacting the surrounding
>>air, an extremely poor thermal conductor with a low thermal mass. So,
>>there's simply no place for the heat to go, unless you'r leaning up
>>against a metal door the whole time with your sweaty body.
>>Evaporation is the answer.
>>
>>- bc
>
>
> FFID here, and that's almost exactly what I was saying to Falooley which
> fomented this question in the first place. I'm saying the cooling effect
> is from the conduction of the heat from your body to the sweat. The air is
> a good insulator, so to remove the heat quickly you wipe away the sweat
> since it takes a long time for it to evaporate, during which all that heat
> energy is sitting on your skin. If you want to cool off don't wait for
> evaporation, wipe off the sweat and you'll feel cooler faster.
>
> Oh yeah, and if I can convince you stop ****ing calling me FFID...I'm not in
> denial you mooks.
>
> -FFNID

Jockeying for an IOM nomination? This is pretty basic stuff you're
getting wrong here.

--
spammage trappage: replace fishies_ with yahoo

Bob Falooley wrote:

> bc wrote:
>
>> Conduction to what? Even though the specific heat of water
>> is very high, the thermal mass of the sweat is way too
>> small to sink any large amount of heat from your skin by
>> itself. So, for the water to be conducting heat from your
>> skin, it must be conducting it to something else with a
>> large thermal mass and low thermal resistance. But,
>> besides your own skin, the sweat is only contacting the
>> surrounding air, an extremely poor thermal conductor with a
>> low thermal mass. So, there's simply no place for the heat
>> to go, unless you'r leaning up against a metal door the
>> whole time with your sweaty body. Evaporation is the
>> answer.
>
> FFID here, and that's almost exactly what I was saying to
> Falooley which fomented this question in the first place.
> I'm saying the cooling effect is from the conduction of the
> heat from your body to the sweat. The air is a good
> insulator, so to remove the heat quickly you wipe away the
> sweat since it takes a long time for it to evaporate, during
> which all that heat energy is sitting on your skin. If you
> want to cool off don't wait for evaporation, wipe off the
> sweat and you'll feel cooler faster.

It doesn't work that way. The sweat starts at body
temperature, so your body isn't conducting heat to the sweat.
It's the process of evaporation that cools the skin. Without
the water on the skin, the cooling effect is much reduced.
Now, as to the effect of wiping off excess water, It's a bit
more complicated:

- On one hand, the evaporation of the small amount of
remaining water will cool the skin more than if there were
more water preent. This explains why you think it cools
better.
- On the other hand, the capacity for cooling will be much
reduced, because without sweat on the surface, there's no
evaporational cooling.

Over the long haul (more than 10 seconds to a minute), leaving
the sweat in place will produce a stronger cooling effect than
wiping it off.

> Oh yeah, and if I can convince you stop ****ing calling me
> FFID...I'm not in denial you mooks.
>
> -FFNID

Your buddy Bob started it.

--
-Wayne
PhD, Heat Transfer, MIT

Wayne S. Hill wrote:

> It doesn't work that way. The sweat starts at body
> temperature, so your body isn't conducting heat to the sweat.
> It's the process of evaporation that cools the skin. Without
> the water on the skin, the cooling effect is much reduced.
> Now, as to the effect of wiping off excess water, It's a bit
> more complicated:
>
> - On one hand, the evaporation of the small amount of
> remaining water will cool the skin more than if there were
> more water preent. This explains why you think it cools
> better.
> - On the other hand, the capacity for cooling will be much
> reduced, because without sweat on the surface, there's no
> evaporational cooling.
>
> Over the long haul (more than 10 seconds to a minute), leaving
> the sweat in place will produce a stronger cooling effect than
> wiping it off.

I came up with a simple diagram that I'll try to do ascii, and hope
you're not using a kerning font.

-------- | --------- -------
| body | | | sweat | | air |
-------- | --------- -------
skin ^
^ evaporation
conduction

It is the process of conduction that transfers heat from the body to
the sweat, which is excreted to your skin. The sweat comes out at body
temperature, but it got that way because of conduction inside your body.
As the sweat cools furthur conduction brings heat from your body into it.
Evaporation cools the sweat, but that's outside the body. Evaporation
isn't cooling your body, it is cooling the sweat. Your body heats the
sweat by conduction, the sweat evaporates into the air.

All I'm saying is that the process acting on the body is conduction,
both internal, and to the sweat that cools on the skin. Evaporation takes
place outside, on the outer layer of the sweat. That is why I say it's
conduction that cools the body.

Wiping the sweat off wasn't a good example. I know that now.

>> Oh yeah, and if I can convince you stop ****ing calling me
>> FFID...I'm not in denial you mooks.
>>
>> -FFNID
>
> Your buddy Bob started it.

Well, it's kind of endearing now anyway, though I like FFNID better.

-FFNID (Isn't it time to eat?)

FFNID wrote:

> I came up with a simple diagram that I'll try to do
> ascii, and hope you're not using a kerning font.
>
> -------- | --------- -------
> | body | | | sweat | | air |
> -------- | --------- -------
> skin ^
> ^ evaporation
> conduction
>
> It is the process of conduction that transfers heat
> from the body to the sweat, which is excreted to your skin.
> The sweat comes out at body temperature, but it got that way
> because of conduction inside your body. As the sweat cools
> furthur conduction brings heat from your body into it.
> Evaporation cools the sweat, but that's outside the body.
> Evaporation isn't cooling your body, it is cooling the sweat.

Incorrect.

> Your body heats the sweat by conduction,

As soon as you consume it, not while you're exercising.

> the sweat evaporates into the air.

That much is right.

> All I'm saying is that the process acting on the
> body is conduction, both internal, and to the sweat that
> cools on the skin. Evaporation takes place outside, on the
> outer layer of the sweat. That is why I say it's conduction
> that cools the body.

You could say that conduction from the hotter core of the body
to the cool skin (which is cooled by the evaporation of the
sweat on the skin) cools the body, but the rest of your argument
is incorrect.

--
-Wayne

On Tue, 10 Feb 2004 22:10:15 -0500, Bob Falooley >
wrote:

>Wayne S. Hill wrote:
>
>> It doesn't work that way. The sweat starts at body
>> temperature, so your body isn't conducting heat to the sweat.
>> It's the process of evaporation that cools the skin. Without
>> the water on the skin, the cooling effect is much reduced.
>> Now, as to the effect of wiping off excess water, It's a bit
>> more complicated:
>>
>> - On one hand, the evaporation of the small amount of
>> remaining water will cool the skin more than if there were
>> more water preent. This explains why you think it cools
>> better.
>> - On the other hand, the capacity for cooling will be much
>> reduced, because without sweat on the surface, there's no
>> evaporational cooling.
>>
>> Over the long haul (more than 10 seconds to a minute), leaving
>> the sweat in place will produce a stronger cooling effect than
>> wiping it off.
>
> I came up with a simple diagram that I'll try to do ascii, and hope
>you're not using a kerning font.
>
> -------- | --------- -------
> | body | | | sweat | | air |
> -------- | --------- -------
> skin ^
> ^ evaporation
> conduction
>
> It is the process of conduction that transfers heat from the body to
>the sweat, which is excreted to your skin. The sweat comes out at body
>temperature, but it got that way because of conduction inside your body.
>As the sweat cools furthur conduction brings heat from your body into it.
>Evaporation cools the sweat, but that's outside the body. Evaporation
>isn't cooling your body, it is cooling the sweat. Your body heats the
>sweat by conduction, the sweat evaporates into the air.
>
> All I'm saying is that the process acting on the body is conduction,
>both internal, and to the sweat that cools on the skin. Evaporation takes
>place outside, on the outer layer of the sweat. That is why I say it's
>conduction that cools the body.
>
> Wiping the sweat off wasn't a good example. I know that now.

Yeah. Oddly enough, I'm losing body heat right now through
evaportation of water, yet somehow no sweat at all is beading up on my
skin. Maybe I need to consider the contribution of blackbody
radiation. What do you think?

>>> Oh yeah, and if I can convince you stop ****ing calling me
>>> FFID...I'm not in denial you mooks.
>>>
>>> -FFNID
>>
>> Your buddy Bob started it.
>
> Well, it's kind of endearing now anyway, though I like FFNID better.
>
>-FFNID (Isn't it time to eat?)

---
Proton Soup

"If I drink water I will have to go to the bathroom and
how can I use the bathroom when my people are in bondage?"
-Saddam Hussein

Proton Soup > wrote in message >...
> On Tue, 10 Feb 2004 22:10:15 -0500, Bob Falooley >
> wrote:
>
> >Wayne S. Hill wrote:
> >
> >> It doesn't work that way. The sweat starts at body
> >> temperature, so your body isn't conducting heat to the sweat.
> >> It's the process of evaporation that cools the skin. Without
> >> the water on the skin, the cooling effect is much reduced.
> >> Now, as to the effect of wiping off excess water, It's a bit
> >> more complicated:
> >>
> >> - On one hand, the evaporation of the small amount of
> >> remaining water will cool the skin more than if there were
> >> more water preent. This explains why you think it cools
> >> better.
> >> - On the other hand, the capacity for cooling will be much
> >> reduced, because without sweat on the surface, there's no
> >> evaporational cooling.
> >>
> >> Over the long haul (more than 10 seconds to a minute), leaving
> >> the sweat in place will produce a stronger cooling effect than
> >> wiping it off.
> >
> > I came up with a simple diagram that I'll try to do ascii, and hope
> >you're not using a kerning font.
> >
> > -------- | --------- -------
> > | body | | | sweat | | air |
> > -------- | --------- -------
> > skin ^
> > ^ evaporation
> > conduction
> >
> > It is the process of conduction that transfers heat from the body to
> >the sweat, which is excreted to your skin. The sweat comes out at body
> >temperature, but it got that way because of conduction inside your body.
> >As the sweat cools furthur conduction brings heat from your body into it.
> >Evaporation cools the sweat, but that's outside the body. Evaporation
> >isn't cooling your body, it is cooling the sweat. Your body heats the
> >sweat by conduction, the sweat evaporates into the air.
> >
> > All I'm saying is that the process acting on the body is conduction,
> >both internal, and to the sweat that cools on the skin. Evaporation takes
> >place outside, on the outer layer of the sweat. That is why I say it's
> >conduction that cools the body.
> >
> > Wiping the sweat off wasn't a good example. I know that now.
>
> Yeah. Oddly enough, I'm losing body heat right now through
> evaportation of water, yet somehow no sweat at all is beading up on my
> skin. Maybe I need to consider the contribution of blackbody
> radiation. What do you think?
>

Only if you're black. Sorry, couldn't resist.

So, I'm impressed that our FFID thinks he should argue heat transfer
with Wayne. I'm just a little ol' EE, but Wayne is the expert. Maybe
we should cross-post to a physics group to really have some fun with
this.

- bc

Proton Soup wrote:

>
> Yeah. Oddly enough, I'm losing body heat right now through
> evaportation of water, yet somehow no sweat at all is beading up on my
> skin. Maybe I need to consider the contribution of blackbody
> radiation. What do you think?
>

This, is really Falooley.

My work buddy's ferver over this issue has grown, he has included our boss
on the subject who has is own theory as well. Currently FFNID is dreaming
up examples to prove his theory, I am sure he will he will post them soon,
maybe even under his own name?

--Falooley

Wayne S. Hill wrote:


> Incorrect.

This is FFNID. Just got back from lunch, and I have to hurry because
I've got my afternoon lunch in a few minutes.

OK, please explain the difference in these three examples:

1: Swimming in a big cool ocean of water. The major influence
affecting your body temperature here is conduction.
2: Taking a shower with cool water flowing across your body. The
major influence affecting your body temperature here is conduction.
3: Sweat sitting on your skin. You say evaporation, but I say it's no
different that #1 & #2.

If you don't think the first two are conduction then please explain
why.

I don't see any salient difference between the three examples. In all
cases we have a skin to liquid boundary across which there is a temperature
gradient, and conduction.

I don't understand where the inconsistent notion of discussing how
the liquid on the skin got the temperature gradient in the first place only
in example #3. I.e. you say we're cooled by evaporation in #3, but not by
global evaporation in #1, or subterranean dirt temperature in #2. In all
three cases we're cooled by the same process.

If as you say, conduction is not involved then lets take it out of the
equation. What good does cool sweat do on my skin if I can't conduct heat
to it; it's not possible to remove the heat without conduction. If, on the
other hand we remove evaporation then I'm still able to cool off by
splashing with cold water...etc.

FFNID (damn I'm hungry, what is this sweat thing anyway)

--
--Falooley

bc wrote:

> Maybe we should cross-post to a physics group
> to really have some fun with this.

Physicists aren't great with heat transfer, by and large. They
know about the mechanisms, of course, but have no feel for the
relative scale of the effects.

--
-Wayne

Bob Falooley wrote:

> Wayne S. Hill wrote:
>
>> Incorrect.
>
> This is FFNID. Just got back from lunch, and I have
> to hurry because I've got my afternoon lunch in a few
> minutes.

You skipped elevenses, didn't you?

> OK, please explain the difference in these three
> examples:
>
> 1: Swimming in a big cool ocean of water. The
> major influence affecting your body temperature here is
> conduction.

You have to draw your system boundary more carefully. The
mechanisms within the body that cause cooling are a mixture of
convection and conduction. What matters in cooling the body is
what causes the surface of the body to be cooler than the body's
core temperature. In swimming, the mechanism is convection.

> 2: Taking a shower with cool water flowing across
> your body. The major influence affecting your body
> temperature here is conduction.

Convection again.

> 3: Sweat sitting on your skin. You say
> evaporation, but I say it's no different that #1 & #2.

Here, it's also a convective mechanism, in that the sweat is
carried away as vapor, but the specific mechanism is usually
simply called evaporation. The actual temperature of the skin
is complicated, because it depends on rate-limited mechanisms,
but if you were just wet (but not hot), the surface temperature
would approach the air's dew point, which is usually much cooler
than body temperature. As your heat rejection rate increases,
the skin temperature increases. It's complicated.

> If you don't think the first two are conduction then
> please explain why.
>
> I don't see any salient difference between the three
> examples. In all cases we have a skin to liquid boundary
> across which there is a temperature gradient, and
> conduction.
>
> I don't understand where the inconsistent notion of
> discussing how the liquid on the skin got the temperature
> gradient in the first place only in example #3. I.e. you
> say we're cooled by evaporation in #3, but not by global
> evaporation in #1, or subterranean dirt temperature in #2.
> In all three cases we're cooled by the same process.

<shudder>

> If as you say, conduction is not involved

I didn't say that. You assumed that's what I meant when I said
you were incorrect.

> then lets
> take it out of the equation. What good does cool sweat do
> on my skin if I can't conduct heat to it; it's not possible
> to remove the heat without conduction. If, on the other
> hand we remove evaporation then I'm still able to cool off
> by splashing with cold water...etc.

<sigh>

--
-Wayne

On 12 Feb 2004 00:12:14 GMT, "Wayne S. Hill" > wrote:

>bc wrote:
>
>> Maybe we should cross-post to a physics group
>> to really have some fun with this.
>
>Physicists aren't great with heat transfer, by and large. They
>know about the mechanisms, of course, but have no feel for the
>relative scale of the effects.

Kinda like taking supplements vs diet and exercise huh?

- bc

Bob Falooley wrote:
> Wayne S. Hill wrote:
>
>
>
>>Incorrect.
>
>
> This is FFNID. Just got back from lunch, and I have to hurry because
> I've got my afternoon lunch in a few minutes.
>
> OK, please explain the difference in these three examples:
>
> 1: Swimming in a big cool ocean of water. The major influence
> affecting your body temperature here is conduction.
> 2: Taking a shower with cool water flowing across your body. The
> major influence affecting your body temperature here is conduction.
> 3: Sweat sitting on your skin. You say evaporation, but I say it's no
> different that #1 & #2.
>
> If you don't think the first two are conduction then please explain
> why.
>
> I don't see any salient difference between the three examples. In all
> cases we have a skin to liquid boundary across which there is a temperature
> gradient, and conduction.

That's because you're ignorant. We're not going to go over basic stuff
you should have learned in high school or first year of university. Go
to your library if you're unable to find the information online. Start
looking for chapters with the terms evaporation and average kinetic energy.



--
spammage trappage: replace fishies_ with yahoo

This is FFNID.

Wayne S. Hill wrote:

> You skipped elevenses, didn't you?

Only on Wednesdays because I'm saving room for all-you-can-eat night
at the local Sizzler.

> You have to draw your system boundary more carefully. The
> mechanisms within the body that cause cooling are a mixture of
> convection and conduction. What matters in cooling the body is
> what causes the surface of the body to be cooler than the body's
> core temperature. In swimming, the mechanism is convection.

Let's make ice cubes against skin example #4, because you certainly
can't argue that there's convection going on when I hold an ice cube against
my skin. The absorption of heat by the ice cube occurs due to conduction.
Maybe you'll say that the ice melts, so substitute a chilled block of
silver metal held against the skin; heat transfer from the body to the
silver is via conduction until equilibrium.

This is a diagram taken verbatim from a few messages back in this
thread. Do you not see the system boundary (represented by a column of "|"
characters labeled "skin" between the "body" and "sweat" boxes)? The
boundary is the top layer of epidermis, where epidermis ends and the
outside begins. Everything inside (inclusive) the top layer of the
epidermis is the body.

-------- | --------- -------
| body | | | sweat | | air |
-------- | --------- -------
skin ^
^ evaporation
conduction

I agree that the dominant sweating mechanism *outside* the body is
convection, but I am not saying that it isn't. I agree that both
convection and conduction are factors inside the body (I failed to specify
convection as an internal mechanism a few messages back, but it is indeed
one). Once sweat is outside and cooling due to convection, the dominant
mechanism for moving heat from your body into the cooling sweat is
conduction. This is the same conduction that would take place if swiming,
or showering or holding a block of silver against the skin(#1 and #2 from
previous message, #4 this message). The sweat on the body does not cool
without convection, but that's mostly at the outside edge of the sweat
layer; the sweat on the body cools and doesn't heat up again without
conduction of additional heat from the body --the continual heating of the
sweat is what cools the body.

I don't think radiant heat is a significant factor.

Generally (not an ad hominem) I think people cling to the notion of
evaporation cooling the body because that's what they were told in
elementary school science; I find this explanation to be an inconsistent
use of nomenclature. Evaporation is a convection that happens outside the
body, and it cools what is cooling the body. Holding an ice cube against
my skin is not an example of the refrigerator's cooling system removing
heat from my body.

>> 2: Taking a shower with cool water flowing across
>> your body. The major influence affecting your body
>> temperature here is conduction.
>
> Convection again.

Again, convection is what takes the heat away once it's outside your
body. Heat transfers outside your body to the cool water via conduction.

>> 3: Sweat sitting on your skin. You say
>> evaporation, but I say it's no different that #1 & #2.
>
> Here, it's also a convective mechanism, in that the sweat is
> carried away as vapor, but the specific mechanism is usually
> simply called evaporation. The actual temperature of the skin
> is complicated, because it depends on rate-limited mechanisms,
> but if you were just wet (but not hot), the surface temperature
> would approach the air's dew point, which is usually much cooler
> than body temperature. As your heat rejection rate increases,
> the skin temperature increases. It's complicated.

Again, the convection mechanism removing the sweat is not the issue.
The issue I'm addressing is transferring heat from the body into the sweat
as it cools. Conduction is what cools the body because it acts directly on
the body; convection acts on the sweat, not on the body.

> <shudder>

Could you be more specific?

>
>> If as you say, conduction is not involved
>
> I didn't say that. You assumed that's what I meant when I said
> you were incorrect.

The mechanism at the boundary of the body<->outside system is
conduction. I think you were correct when you mentioned boundary definition
as being the issue. It might be debatable whether sweat that has been
excreted is still considered part of your body, and that may be the source
of our disagreement. Are you really saying that sweat that's been excreted
is still part of the body? Does this apply to all excretions, or just
sweat? Excepting the diagram, which I thought was clear, from a few
messages back I never explicitly stated that I don't consider excreted
sweat part of the body: I don't consider excreted sweat part of the body.

> <sigh>

Could you be more specific?

FFNID (Dude where's my dinner?)

"Rastarr" > wrote in message >...

>
> OK, WTF is a FFID ?
>

Heh-heh, I'll bet this has all been very frustrating.

F - Jack Sprat couldn't eat it.
F - The secnod word in your TLA above.
I - What you say when you don't fold: "I'm ___"
D - Not just a river in Egypt.

- bc

Bob Falooley wrote:

> This is FFNID.
>
> Wayne S. Hill wrote:
>
>> You have to draw your system boundary more carefully. The
>> mechanisms within the body that cause cooling are a mixture
>> of convection and conduction. What matters in cooling the
>> body is what causes the surface of the body to be cooler
>> than the body's core temperature. In swimming, the
>> mechanism is convection.
>
> Let's make ice cubes against skin example #4,
> because you certainly can't argue that there's convection
> going on when I hold an ice cube against my skin. The
> absorption of heat by the ice cube occurs due to conduction.
> Maybe you'll say that the ice melts, so substitute a chilled
> block of silver metal held against the skin; heat transfer
> from the body to the silver is via conduction until
> equilibrium.

Yeah, OK, and?

> This is a diagram taken verbatim from a few messages
> back in this thread. Do you not see the system boundary
> (represented by a column of "|" characters labeled "skin"
> between the "body" and "sweat" boxes)? The boundary is the
> top layer of epidermis, where epidermis ends and the outside
> begins. Everything inside (inclusive) the top layer of the
> epidermis is the body.
>
> -------- | --------- -------
> | body | | | sweat | | air |
> -------- | --------- -------
> skin ^
> ^ evaporation
> conduction
>
> I agree that the dominant sweating mechanism
> *outside* the body is convection, but I am not saying that
> it isn't. I agree that both convection and conduction are
> factors inside the body (I failed to specify convection as
> an internal mechanism a few messages back, but it is indeed
> one). Once sweat is outside and cooling due to convection,
> the dominant mechanism for moving heat from your body into
> the cooling sweat is conduction. This is the same
> conduction that would take place if swiming, or showering or
> holding a block of silver against the skin(#1 and #2 from
> previous message, #4 this message). The sweat on the body
> does not cool without convection, but that's mostly at the
> outside edge of the sweat layer; the sweat on the body cools
> and doesn't heat up again without conduction of additional
> heat from the body --the continual heating of the sweat is
> what cools the body.

OK, so ... ?

> I don't think radiant heat is a significant factor.

You might be surprised. In quiescent conditions at room
temperature, radiation comprises about 1/3 of total heat
transfer

> Generally (not an ad hominem) I think people cling
> to the notion of evaporation cooling the body because that's
> what they were told in elementary school science; I find
> this explanation to be an inconsistent use of nomenclature.
> Evaporation is a convection that happens outside the body,
> and it cools what is cooling the body. Holding an ice cube
> against my skin is not an example of the refrigerator's
> cooling system removing heat from my body.

Fine. And your point is?

>>> 2: Taking a shower with cool water flowing across
>>> your body. The major influence affecting your body
>>> temperature here is conduction.
>>
>> Convection again.
>
> Again, convection is what takes the heat away once
> it's outside your body. Heat transfers outside your body to
> the cool water via conduction.
>
>>> 3: Sweat sitting on your skin. You say
>>> evaporation, but I say it's no different that #1 & #2.
>>
>> Here, it's also a convective mechanism, in that the sweat
>> is carried away as vapor, but the specific mechanism is
>> usually simply called evaporation. The actual temperature
>> of the skin is complicated, because it depends on
>> rate-limited mechanisms, but if you were just wet (but not
>> hot), the surface temperature would approach the air's dew
>> point, which is usually much cooler than body temperature.
>> As your heat rejection rate increases, the skin temperature
>> increases. It's complicated.
>
> Again, the convection mechanism removing the sweat
> is not the issue. The issue I'm addressing is transferring
> heat from the body into the sweat as it cools. Conduction
> is what cools the body because it acts directly on the body;
> convection acts on the sweat, not on the body.

Fine and dandy.
>
>> <shudder>
>
> Could you be more specific?


Sure. WHAT IS YOUR POINT? Falooley said you believed that the
body cooled better if you wiped off the sweat. How does all the
blather above relate to that contention?

>>> If as you say, conduction is not involved
>>
>> I didn't say that. You assumed that's what I meant when I
>> said you were incorrect.
>
> The mechanism at the boundary of the body<->outside
> system is conduction. I think you were correct when you
> mentioned boundary definition as being the issue. It might
> be debatable whether sweat that has been excreted is still
> considered part of your body, and that may be the source of
> our disagreement. Are you really saying that sweat that's
> been excreted is still part of the body? Does this apply to
> all excretions, or just sweat? Excepting the diagram, which
> I thought was clear, from a few messages back I never
> explicitly stated that I don't consider excreted sweat part
> of the body: I don't consider excreted sweat part of the
> body.
>
>> <sigh>
>
> Could you be more specific?

None of this has any bearing on the issue at hand: how you cool
your body most efficiently depends on what happens outside the
body.

--
-Wayne

"Wayne S. Hill" > wrote in message >...
> Bob Falooley wrote:
>
> > Wayne S. Hill wrote:
> >
> >> Incorrect.
> >
> > This is FFNID. Just got back from lunch, and I have
> > to hurry because I've got my afternoon lunch in a few
> > minutes.
>
> You skipped elevenses, didn't you?

Hah! Almost snorted the diet vanilla pepsi. Ow, that hurt.


> snipped lots of really interesting ;} thermo stuff

Apparently, FFID believes that if your skin has sweat on it and you're
cooling off, that can only mean heat conduction from skin to sweat and
that, therefore, you are being cooled by conduction.

I am reaching my rate-limited interest in convincing him otherwise.

- bc

On 12 Feb 2004 23:42:36 GMT, "Wayne S. Hill" > wrote:

>None of this has any bearing on the issue at hand: how you cool
>your body most efficiently depends on what happens outside the
>body.

Well, regulation of blood flow plays a big role, too. Not having
studied it, I don't have a feel for percentages and whatnot, but we
wouldn't be able to maintain stable core temps without it.

Proton Soup

Proton Soup wrote:

> On 12 Feb 2004 23:42:36 GMT, "Wayne S. Hill"
> > wrote:
>
>>None of this has any bearing on the issue at hand: how you
>>cool your body most efficiently depends on what happens
>>outside the body.
>
> Well, regulation of blood flow plays a big role, too. Not
> having studied it, I don't have a feel for percentages and
> whatnot, but we wouldn't be able to maintain stable core
> temps without it.

True. This is the convective component of the internal heat
transfer model. My point was that he's obsessing on conduction
heat transfer at the skin surface, which has nothing to do with
his earlier contention that wiping sweat off will cool you
better.

--
-Wayne

This is FFNID.

Wayne S. Hill wrote:

> None of this has any bearing on the issue at hand: how you cool
> your body most efficiently depends on what happens outside the
> body.

All of this has direct bearing. The original question was:

Bob Falooley wrote:

> So, does sweat cool your body through evaporation, or conduction, or
> probably both?

The correct answer to this question is that the sweat cools the body via
conduction. The sweat itself is cooled by external processes that act upon
the sweat and do not involve the body.

As for wiping off the sweat, I addressed that several messages back:

FFNID wrote:

> Wiping the sweat off wasn't a good example. I know that now.

The wiping off the sweat example fails because it is an example of the
external process, not the conduction. Wiping off the sweat can increase
the evaporation of the sweat by distributing the remaining sweat more
evenly and thus might make you feel cooler, but you feel cooler because the
skin/sweat temperature gradient increases. It is still conduction between
the body and the cooler sweat.

-FFNID (Time for breakfast)

This is FFNID.

Wayne S. Hill wrote:

> True. This is the convective component of the internal heat
> transfer model. My point was that he's obsessing on conduction
> heat transfer at the skin surface, which has nothing to do with
> his earlier contention that wiping sweat off will cool you
> better.

I have stated in at least two messages that the wiping off sweat was a
bad example of my point. See this quote:

FFNID wrote:

> Wiping the sweat off wasn't a good example. I know that now.

Wiping off sweat is an example of accelerating evaporation by thinning
the layer of sweat, and increasing the surface area of the sweat that
remains after wiping. I acknowledge that wiping off sweat is an incorrect
example of conduction. I mentioned wiping off sweat as an example in
exactly one message, and have retracted it ever since. You keep
conveniently forgetting this portion of the original message where I
mentioned wiping off sweat:

FFNID wrote:

> FFID here, and that's almost exactly what I was saying to Falooley which
> fomented this question in the first place. I'm saying the cooling effect
> is from the conduction of the heat from your body to the sweat. <snip>

Again, the original question posed by Bob was:

Bob Falooley wrote:

> So, does sweat cool your body through evaporation, or conduction, or
> probably both?

It is not obsessing to insist on rigorous specification of the correct
mechanism of heat transfer for sweat cooling the body. Of the three means
of transferring heat, conduction is the most important when we're
discussing a cool liquid on the skin. The question does not ask "how does
the sweat get cooler than the body?"

The knee-jerk response "evaporation cools the body" is inconsistent and
incorrect. That was, is, and will continue to be my point.

FFNID (Back from breakfast, and ready for elevenses)

On Fri, 13 Feb 2004 10:03:10 -0500, Bob Falooley >
wrote:

>This is FFNID.
>
>Wayne S. Hill wrote:
>
>> True. This is the convective component of the internal heat
>> transfer model. My point was that he's obsessing on conduction
>> heat transfer at the skin surface, which has nothing to do with
>> his earlier contention that wiping sweat off will cool you
>> better.
>
> I have stated in at least two messages that the wiping off sweat was a
>bad example of my point. See this quote:
>
>FFNID wrote:
>
>> Wiping the sweat off wasn't a good example. I know that now.
>
> Wiping off sweat is an example of accelerating evaporation by thinning
>the layer of sweat, and increasing the surface area of the sweat that
>remains after wiping. I acknowledge that wiping off sweat is an incorrect
>example of conduction. I mentioned wiping off sweat as an example in
>exactly one message, and have retracted it ever since. You keep
>conveniently forgetting this portion of the original message where I
>mentioned wiping off sweat:
>
>FFNID wrote:
>
>> FFID here, and that's almost exactly what I was saying to Falooley which
>> fomented this question in the first place. I'm saying the cooling effect
>> is from the conduction of the heat from your body to the sweat. <snip>
>
> Again, the original question posed by Bob was:
>
>Bob Falooley wrote:
>
>> So, does sweat cool your body through evaporation, or conduction, or
>> probably both?
>
> It is not obsessing to insist on rigorous specification of the correct
>mechanism of heat transfer for sweat cooling the body. Of the three means
>of transferring heat, conduction is the most important when we're
>discussing a cool liquid on the skin. The question does not ask "how does
>the sweat get cooler than the body?"
>
> The knee-jerk response "evaporation cools the body" is inconsistent and
>incorrect. That was, is, and will continue to be my point.
>
>FFNID (Back from breakfast, and ready for elevenses)

You really need to go back to changing light bulbs or whatever it was
you were doing before this discussion started. When the temperature
gets up to 100 F, all the conduction in world won't keep you alive, no
matter how much you sweat. If there's not some serious evaporation
going on, you'll soon be dead.

Proton Soup

This is FFNID.

Proton Soup <> wrote:

> You really need to go back to changing light bulbs or whatever it was
> you were doing before this discussion started. When the temperature
> gets up to 100 F, all the conduction in world won't keep you alive, no
> matter how much you sweat. If there's not some serious evaporation
> going on, you'll soon be dead.

All of the evaporation in the world won't keep you alive at any
temperature if you cannot conduct heat across the skin barrier. Without
conduction the human body becomes closed to heat transfer except via
radiation(1). However, without evaporation you can still use any other
heat-sync methods; cool sweat is just another sync, but the heat moves to
the sync via conduction. Conduction is what cools the body.

(1)You get not insignificant cooling via respiration too, but that's beyond
this scope of skin cooling.

FFNID

On Fri, 13 Feb 2004 15:52:07 -0500, Bob Falooley >
wrote:

>This is FFNID.
>
>Proton Soup <> wrote:
>
>> You really need to go back to changing light bulbs or whatever it was
>> you were doing before this discussion started. When the temperature
>> gets up to 100 F, all the conduction in world won't keep you alive, no
>> matter how much you sweat. If there's not some serious evaporation
>> going on, you'll soon be dead.
>
> All of the evaporation in the world won't keep you alive at any
>temperature if you cannot conduct heat across the skin barrier. Without
>conduction the human body becomes closed to heat transfer except via
>radiation(1). However, without evaporation you can still use any other
>heat-sync methods; cool sweat is just another sync, but the heat moves to
>the sync via conduction. Conduction is what cools the body.
>
>(1)You get not insignificant cooling via respiration too, but that's beyond
>this scope of skin cooling.

I think you missed the point entirely. We know all about conduction,
especially Wayne, but the magic of keeping humans cool revolves around
the physics of evaporation, that is, the huge amount of calories
absorbed by H2O as it makes a phase change from liquid to vapor. In
fact, it's the only thing that generates "cool sweat" when the temp of
the atmosphere gets above your body temp.

And sure, I suppose breathing would cool you, even though I hadn't
really considered it. But the primary mechanism is still the phase
change of water to vapor as you breathe. It's a little more
complicated, though. You've got other things going on like the nose
acting as a preheater/humidifier for incoming air, which is especially
important in cold climates.

Proton Soup

On Fri, 13 Feb 2004 15:52:07 -0500, Bob Falooley >
wrote:

>However, without evaporation you can still use any other
>heat-sync methods

Almost forgot, it's a heat "sink".

Proton Soup

On 13 Feb 2004 01:06:08 GMT, "Wayne S. Hill" > wrote:

>Proton Soup wrote:
>
>> On 12 Feb 2004 23:42:36 GMT, "Wayne S. Hill"
>> > wrote:
>>
>>>None of this has any bearing on the issue at hand: how you
>>>cool your body most efficiently depends on what happens
>>>outside the body.
>>
>> Well, regulation of blood flow plays a big role, too. Not
>> having studied it, I don't have a feel for percentages and
>> whatnot, but we wouldn't be able to maintain stable core
>> temps without it.
>
>True. This is the convective component of the internal heat
>transfer model. My point was that he's obsessing on conduction
>heat transfer at the skin surface, which has nothing to do with
>his earlier contention that wiping sweat off will cool you
>better.


All he need do is look at the difference between heat of evaporation
(ca. +44 kJ/mol) vs specific heat of water (ca. 75 J/mol). It takes
about 5 times as much energy to evaporate one mole of water as it does
to heat it from 0 to 100 celsius. Hydrogen bonding makes life
possible.

Dr. Dickie
Skepticult member in good standing #394-00596-438
Poking kooks with a pointy stick
====================================
"Let be be finale of seem.
The only emperor is the emperor of ice-cream"
Wallace Stevens-1923
=====================================

(Peter Allen) wrote in message >...
> Bob Falooley > wrote in message >...
> > So, does sweat cool your body through evaporation, or conduction, or
> > probably both?
> >
> > So If I am sweating and I want to use it the most efficient way to cool
> > myself, I shouldn't wipe it off?
>
> Evaporation: so you should stand in front of a fan to get cool. If
> you're wanting to wipe the sweat off for comfort, it's fine, though -
> you only need enough sweat to cover the skin, and you'll have that
> very soon after wiping anyway.
>
> Peter

"Heat of Evaporation" is at work here. It is the evaporation of water
in the sweat that is removing excess heat from the body - not just the
sweat moving heat from the body's core to an outside heat sink.

The following example may shed some light on the fallacy of the
conduction only theory.

Let's say you (at 98.6 degrees) are standing outside in Phoenix Az
where the summer temperature is 110 degrees. Well if not for the
"heat of evaporation" you would be conducting (or whatever) the 110
heat to your body until an equilibrium with the environment was
reached. When you consider the large heat mass around you, you would
eventually reach 110 degrees. But, This does not happen in a living
human that is in good health and well hydrated so something else must
be at work. And yes this is the "heat of evaporation" as the sweat
evaporates to cool the body. Degrees in the above example are
obviously in Fahrenheit.

The heat of evaporation of water - as the water in the sweat moves
from a liquid state to a vapor state - releases large amounts of heat
and is able to cool the body.

As I recall this is covered in Freshman Chemistry in College. I'm an
EE so I do not regularly work with the formulas. I suggest that
anyone with an in interest in cooling via evaporation go to your local
library to do some research, or perhaps google search "heat of
evaporation." A related topic is the "heat of fusion." This is
moving between solid and liquid states of matter.

Cheers,

Greg

This is FFNID.

Proton Soup <> wrote:

> I think you missed the point entirely. We know all about conduction,
> especially Wayne, but the magic of keeping humans cool revolves around
> the physics of evaporation, that is, the huge amount of calories
> absorbed by H2O as it makes a phase change from liquid to vapor. In
> fact, it's the only thing that generates "cool sweat" when the temp of
> the atmosphere gets above your body temp.

I'm the one making the point, and you've missed it. I've never argued
that evaporation doesn't exist, or that it doesn't remove heat from the
sweat on the skin. What I'm saying is that it's incorrect to say that
evaporation cools the body since evaporation doesn't act on the body. The
only(1) heat transfer mechanism acting directly on the body when cooling
through sweat is conduction of heat to the sweat as it cools on the skin,
so the body is cooled through conduction.

Swimming in the cool ocean, soaking in a cool bath, holding a chilled
block of silver against the skin, and cooling via sweat are all examples of
the same heat transfer mechanism at work. This is conduction to the
external sink regardless of what the sink is, or how it got a temperature
gradient versus the skin.

I mean, where do you draw the line on what external mechanisms to
include? If you say evaporation cools the body then why not say that
evaporation was aided by a fan, and since the fan is powered by electricity
maybe the power company turbine is cooling me? Since there would be no
weather patterns without the Sun, is it OK to say the Sun cools me because
of the nice breeze? How about <insert outrageous tangential external
process here> cooling the body? These are all external processes, and it
would be absurd to talk about them cooling the body. The only mechanism
that is correct in all of the above exaggerations *and* in the realistic
examples from the previous paragraph is still conduction because conduction
is the only transfer mechanism acting directly on the body(2).

What I am advocating is the specification of the correct heat transfer
mechanism. Ultimately I think it makes things less complicated to
understand, but for the bias of having learned "evaporation cools the body"
in elementary science class. Regardless of whether it's easier to
understand or not, it is conduction removing heat from the body.

(1) There are no absolutes, but for the scope of skin cooling this is true.
(2) Again, no absolutes so this is only relevant to skin cooling, and
simplified even for that.

> And sure, I suppose breathing would cool you, even though I hadn't
> really considered it. But the primary mechanism is still the phase
> change of water to vapor as you breathe. It's a little more
> complicated, though. You've got other things going on like the nose
> acting as a preheater/humidifier for incoming air, which is especially
> important in cold climates.

I only mentioned respiration to be complete. This is OT, but I think
respiration is what helps keep you from over heating in a hot tub, and
keeps you alive (on your way out though) even at 110 degrees water
temperature. I'm guessing that internal convection is minimized by
reducing blood flow close to the skin, while simultaneously speeding blood
flow to the lungs, and maybe breathing faster. I'm not sure though, so
just $0.02.

FFNID (Time for dinner...seriously)

This is FFNID. So, since the thread is cooling down some I've had time to
browse the backlog a bit.

Wayne S. Hill wrote:

>> Your body heats the sweat by conduction,
>
> As soon as you consume it, not while you're exercising.

The second half of this sentence is absolutely incorrect. Sweat
emerges from your body at body temperature and cools on your skin. Without
adding more heat to the cooling sweat (via conduction, but you knew I was
going to say that) it does you no good. Heat continues to be added to the
sweat as long as it is cooling on your skin. Heat is indeed added to the
sweat "while you're exercising."

I'm suprised you'd get that one wrong.

FFNID --Too late for dinner now, the 24-hour Chinese on 14th closes at 10:00
on Monday.

In article >,
Wayne S. Hill > wrote:

>It doesn't work that way. The sweat starts at body
>temperature, so your body isn't conducting heat to the sweat.
>It's the process of evaporation that cools the skin. Without
>the water on the skin, the cooling effect is much reduced.
>Now, as to the effect of wiping off excess water, It's a bit
>more complicated:
>
> - On one hand, the evaporation of the small amount of
>remaining water will cool the skin more than if there were
>more water preent. This explains why you think it cools
>better.
> - On the other hand, the capacity for cooling will be much
>reduced, because without sweat on the surface, there's no
>evaporational cooling.
>
>Over the long haul (more than 10 seconds to a minute), leaving
>the sweat in place will produce a stronger cooling effect than
>wiping it off.

That depends [$1 to Lyle]. If you're still sweating, wiping off the
existing sweat doesn't lose cooling effect. And if you're not still
sweating, you don't need the cooling effect.

Seth
--
Don't ever masturbate after getting capsaicin on your hands. -- Patrick Arnold

In article >,
Wayne S. Hill > wrote:

>It doesn't work that way. The sweat starts at body
>temperature, so your body isn't conducting heat to the sweat.
>It's the process of evaporation that cools the skin. Without
>the water on the skin, the cooling effect is much reduced.
>Now, as to the effect of wiping off excess water, It's a bit
>more complicated:
>
> - On one hand, the evaporation of the small amount of
>remaining water will cool the skin more than if there were
>more water preent. This explains why you think it cools
>better.
> - On the other hand, the capacity for cooling will be much
>reduced, because without sweat on the surface, there's no
>evaporational cooling.
>
>Over the long haul (more than 10 seconds to a minute), leaving
>the sweat in place will produce a stronger cooling effect than
>wiping it off.

That depends [$1 to Lyle]. If you're still sweating, wiping off the
existing sweat doesn't lose cooling effect. And if you're not still
sweating, you don't need the cooling effect.

Seth
--
Don't ever masturbate after getting capsaicin on your hands. -- Patrick Arnold

Seth Breidbart wrote:

> Wayne S. Hill > wrote:
>
>>Over the long haul (more than 10 seconds to a minute),
>>leaving the sweat in place will produce a stronger cooling
>>effect than wiping it off.
>
> That depends [$1 to Lyle]. If you're still sweating, wiping
> off the existing sweat doesn't lose cooling effect. And if
> you're not still sweating, you don't need the cooling
> effect.
>
> Seth

30 days.

--
-Wayne

Seth Breidbart wrote:

> Wayne S. Hill > wrote:
>
>>Over the long haul (more than 10 seconds to a minute),
>>leaving the sweat in place will produce a stronger cooling
>>effect than wiping it off.
>
> That depends [$1 to Lyle]. If you're still sweating, wiping
> off the existing sweat doesn't lose cooling effect. And if
> you're not still sweating, you don't need the cooling
> effect.
>
> Seth

30 days.

--
-Wayne

In article >,
Bob Falooley > wrote:

> OK, please explain the difference in these three examples:
>
> 1: Swimming in a big cool ocean of water. The major influence
>affecting your body temperature here is conduction.
> 2: Taking a shower with cool water flowing across your body. The
>major influence affecting your body temperature here is conduction.
> 3: Sweat sitting on your skin. You say evaporation, but I say it's no
>different that #1 & #2.

In #1, the heat you put into the ocean has no effect on its
temperature.

In #2, the heat you put into the water has no effect on the
temperature of the water that hits you next.

In #3, the heat you put into the sweat raises its temperature because
you significantly outweigh it. Evaporation cools the sweat; without
evaporation, equilibrium would rapidly be reached (indeed, you'd start
there) and sweating wouldn't lower your temperature.

> I don't see any salient difference between the three examples. In all
>cases we have a skin to liquid boundary across which there is a temperature
>gradient, and conduction.

It's given (by you) that the ocean water and shower water have a cool
temperature to begin with. Your heat transfer doesn't affect those.
However, your sweat starts at body (skin) temperature, so any cooling
effect must start with lowering the temperature of the sweat.

Seth
--
Don't ever masturbate after getting capsaicin on your hands. -- Patrick Arnold

In article >,
Bob Falooley > wrote:

> OK, please explain the difference in these three examples:
>
> 1: Swimming in a big cool ocean of water. The major influence
>affecting your body temperature here is conduction.
> 2: Taking a shower with cool water flowing across your body. The
>major influence affecting your body temperature here is conduction.
> 3: Sweat sitting on your skin. You say evaporation, but I say it's no
>different that #1 & #2.

In #1, the heat you put into the ocean has no effect on its
temperature.

In #2, the heat you put into the water has no effect on the
temperature of the water that hits you next.

In #3, the heat you put into the sweat raises its temperature because
you significantly outweigh it. Evaporation cools the sweat; without
evaporation, equilibrium would rapidly be reached (indeed, you'd start
there) and sweating wouldn't lower your temperature.

> I don't see any salient difference between the three examples. In all
>cases we have a skin to liquid boundary across which there is a temperature
>gradient, and conduction.

It's given (by you) that the ocean water and shower water have a cool
temperature to begin with. Your heat transfer doesn't affect those.
However, your sweat starts at body (skin) temperature, so any cooling
effect must start with lowering the temperature of the sweat.

Seth
--
Don't ever masturbate after getting capsaicin on your hands. -- Patrick Arnold

In article >,
Wayne S. Hill > wrote:
>Seth Breidbart wrote:
>> Wayne S. Hill > wrote:
>>
>>>Over the long haul (more than 10 seconds to a minute),
>>>leaving the sweat in place will produce a stronger cooling
>>>effect than wiping it off.
>>
>> That depends [$1 to Lyle]. If you're still sweating, wiping
>> off the existing sweat doesn't lose cooling effect. And if
>> you're not still sweating, you don't need the cooling
>> effect.
>>
>> Seth
>
>30 days.

New record?

Seth
--
chown -R us /yourbase

In article >,
Wayne S. Hill > wrote:
>Seth Breidbart wrote:
>> Wayne S. Hill > wrote:
>>
>>>Over the long haul (more than 10 seconds to a minute),
>>>leaving the sweat in place will produce a stronger cooling
>>>effect than wiping it off.
>>
>> That depends [$1 to Lyle]. If you're still sweating, wiping
>> off the existing sweat doesn't lose cooling effect. And if
>> you're not still sweating, you don't need the cooling
>> effect.
>>
>> Seth
>
>30 days.

New record?

Seth
--
chown -R us /yourbase

Seth Breidbart wrote:

> Wayne S. Hill > wrote:
>>Seth Breidbart wrote:
>>> Wayne S. Hill > wrote:
>>>
>>>>Over the long haul (more than 10 seconds to a minute),
>>>>leaving the sweat in place will produce a stronger cooling
>>>>effect than wiping it off.
>>>
>>> That depends [$1 to Lyle]. If you're still sweating,
>>> wiping off the existing sweat doesn't lose cooling effect.
>>> And if you're not still sweating, you don't need the
>>> cooling effect.
>>>
>>> Seth
>>
>>30 days.
>
> New record?

Not at all. You're back on schedule.

--
-Wayne

Seth Breidbart wrote:

> Wayne S. Hill > wrote:
>>Seth Breidbart wrote:
>>> Wayne S. Hill > wrote:
>>>
>>>>Over the long haul (more than 10 seconds to a minute),
>>>>leaving the sweat in place will produce a stronger cooling
>>>>effect than wiping it off.
>>>
>>> That depends [$1 to Lyle]. If you're still sweating,
>>> wiping off the existing sweat doesn't lose cooling effect.
>>> And if you're not still sweating, you don't need the
>>> cooling effect.
>>>
>>> Seth
>>
>>30 days.
>
> New record?

Not at all. You're back on schedule.

--
-Wayne