[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: RT water and heat retention in theory and life

I am sorry about what I accidentally had forgotten to put my name in the mail header.

I would like someone to do calculate upper limit for
respiratory water loss/(metabolic water gain + freed water) ratio.
as I did. I'll post my calcuation later.

Martin Baeker said:

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

Well compare two almost identical animals, one endothermic and other
one ectothermic at same temperature, about 36 deg C. Ectotherms
typically have metabolic speed of about 1/4 of endotherm of same size
(provided that ectotherm is as warm as endotherm).
Isn't the number more like 1/10? At least, 1/10 is the number in the
scaling relation given by Schmid-Nielsen.
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.

Well... someone linked that RTs help heat retention and through that
promote endothermy.
I did a lot of physical activity (like running distances like 5--40 km)
at temperatures as low as -25 deg C and as high as +30 deg C.
At temperatures at -25 deg C, human can overheat if wearing
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?

Most mammals have sweat glands.
If respiratory heat loss is not overhelming at
T diffs (lung-ambient) about 50 deg C, why should it
be for reptile for which T diff is hardly over 3?
Respiratory heat loss is overwhelming in this case - that's why people
in winter tend to muffle their mouths with a shawl (when not jogging,
that is). In addition, the counter-current mechanism also serves to
heat up inbreathed air and the RTs are needed for that as well (and
that's why your mom told you always to breathe through your nose when
outside in winter back when you were a kid).
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.

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.

Dmitry Anisimov