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Re: Sauropod cooling



In article <v01540b09aeb53cf9eb26@[129.127.84.36]>, Van and
Kathy Smith <vksmith@dwx.com> wrote
>Forgive me if this has been brought up before, but as I was taking a shower
>this morning I was struck with an idea of an extremely effective way that
>sauropods could keep cool: evaporative cooling.
>
>For those of you not familiar with evaporative cooling, when air blows over
>a wet body it carries away with it some of the more energetic (hot) water
>molecules leaving behind less energetic (cool) water molecules -- hence the
>water molecules left behind have a lower average energy (or temperature).
>
Evaporative cooling occurs because the process of evaporation
(phase transition of a liquid to a vapour below its boiling point) takes
the latent heat of vaporisation from the substrate. For water this latent
heat is quite big, over 500 calories per gram. This heat is supplied by
the other water molecules which in turn regains some of the heat
from the surrounding material to remain in thermal balance. Thus the
surrounding material also cools.

>Evaporative cooling is used by humans when we sweat and dogs when they
>pant.  It is also used by humans through "a poor man's air conditioner"
>widely called "swamp coolers" where air is blown over a pan of water --
>although these were more popular many years ago, I saw a modern version of
>one these this past summer at Best Buy.
>
Sweating itself does not cause cooling - only when the sweat is
evaporated there is a net loss of heat from the body. If sweat does
not evaporate, as happens in very humid condition in an enclosed
area, no cooling takes place. Evaporation stops when the air is
saturated with water vapour.

>Sauropods, with their extremely elongated necks and pneumatic construction,
>would have a tremendously effective evaporative cooling system as air
>passed over the moist membranes of the very long trachea, and, perhaps,
>over the walls of air sacs as well.
>
A long narrow trachea would hold a relatively small volume of air
compared to the surface area to which it is exposed. This volume
would very rapidly get saturated with water vapour and evaporative
cooling would stop. A very rapid breathing will be required to make
evaporative cooling effective. This could be an effective short term
manoeuvre but is unlikely to be solution to chronic overheating.

Gautam Majumdar                 gautam@majumdar.demon.co.uk