Re: RT water and heat retention in theory and life

[Martin Baeker <martin.baeker@tu-bs.de>]

> > I think you miss the point here: RTs serve to cool down the
> > air (by using some counter-current mechanism as in a heat exchanger)
> > and thus allow for heat and moisture retention. Imagine air coming up
> > from the lungs at 100% humidity and T=36ÂC. If the air gets cooled
> > down by the RT's to 20ÂC before exhaling, water will condense inside
> > the nose - I don't have exact formula at hand, but there is a graphic on
> > the German wikipedia site that lets me estimate that about 50% of the
> > water in the air might get out this way. So the temperature difference
> > that is of importance is that between tip of nose and lung.
> Why would RTs be 20ÂC if water condenses on them?

They would be cooled because outside (cold air) is flowing in, cooling
them differentially. I.e., blood at the tip of the nose gets colled by
air and then cools down rest of RTs.

> Where's latent heat of condensation? As you know, it is equal
> to latent heat of evaporation.

With a minus-sign - so if water condensates on the RTs, it will serve
to cool them, not heat them up.

> 1/10 is what is when ectotherms are cooler than endotherms.
> Schmidt-Nielsen gives a separate table of metabotism when body T
> is took same for different animals.

I see.

> > > heavy clothes. THIS MEANS THAT BODY GAINS MORE HEAT THROUGH METABOLISM
> > > THAN IT LOSES THROUGH RESPIRATION. (UNLESS YOU'RE AMPHIBIAN AND BREATHE
> > > THROUGH YOUR SKIN).
> > I don't think this follows, cause animals don't jog all the time -
> > cannot afford the energy. So the fact that you get hot when you are
> > jogging is irrelevant.
> If heat gain/heat loss ratio is grossly more than one for extreme high
> metabolic rates, why should one expect it to be lower than one at
> low metabolic rate?

I was referring to your sentence in caps. If the amount of heat lost
per minute is in a first approximation independent of whether you are
exercising or at rest (let's say the amount is X), than as long as
your heat production is greater than X, you are fine (that's for
running), but if it is less (as in resting), you are cold. So The body
does *not* always gain more heat by metabolism than it loses. How much
of this is lost by respiration cannot be seen from this as far as I
can tell. 

> Well heat loss is very significant for nose, throat and lungs. Because of that
> kids can easily get respiratory infections... But compared to whole organism
> heat loss is barely significant.

How do you know that it is insignificant? Doesn't it depend on how
well insulated the rest of the body is? Do you have numbers for any
kind of animal for this?

> > That's plain wrong. In sweating, you get cooled by the latent heat of
> > the phase transition between liquid and gaseous states, and that's
> > quite a lot. You won't get this if you loose water just by exhaling.
> That's plain wrong. You've forgotten about the law of conservation of energy.
> [Really, should animals follow the laws of void matter? Some
> phylosophers say not.]
> Doesn't water evaporate in lungs? Latent heat is same in both cases.

If all exhaled water is indeed in gaseous state, that's true. But I'm
not sure it is - isn't there some amount of water in exhaled air that
is in form of (micro)-droplets?

Martin.

                   Priv.-Doz. Dr. Martin BÃker
                   Institut fÃr Werkstoffe
                   Technische UniversitÃt Braunschweig
                   Langer Kamp 8
                   38106 Braunschweig
                   Germany
                   Tel.: 00-49-531-391-3073                      
                   Fax   00-49-531-391-3058
                   e-mail <martin.baeker@tu-bs.de>