Re: can of worms

["Augustus T. White" <augwhite@neosoft.com>]

Inman, Don F wrote:
> 
> comment here...
> 
> My forte is not heat transfer and thermodynamics but I don't think that
> analogy works here. I think the car thing has more to do with the
> transparent material (glass) and green house things. Not skin, scales, and
> fur.

I always have trouble with this one, so I have to go back to basics.  
The following is my distant memory of these basics, subject to 
correction by the more recently educated.  

The problem is that we tend to confuse thermal equilibrium with thermal 
steady state.  At equilibrium, all elements of any closed system will 
have the same temperature.  Equilibrium is (among other things) the 
condition an unperturbed system will maintain indefinitely and is the 
condition of maximum entropy.  If temperature were different in two 
different compartments of the system, the T*delS (delG = delH - T*delS?) 
term would differ, allowing for net free energy flow from one compartment 
to the other, violating equilibrium.  However, living organisms are not 
at equilibrium with their thermal environment.  This is good because 
otherwise we'd be dead.

What is true is that, at least locally, a living organism is at steady 
state with respect to its environment.  That is, at any point in the 
system, the temperature is constant over time.  This does *not* require 
that the temperature be the same at each point or that the system be 
closed.  It requires only that the *net* heat flow be zero at all points. 
 OK.  Postulate a spherical horse (a famous punch line -- if you care to 
know, I'll tell you the joke that goes with it) sitting in still 70 deg. 
air and bright sunlight.  The horse has some average thermal thermal 
conductivity and thermal capacity.  It absorbs IR from the sun and 
generates heat energy by metabolism. However, it's conductivity and 
surface area are small.  It'll build up quite a high temperature before 
it can radiate enough heat to equal the inflow from sun and metabolism.  
This temperature can't be calculated on this data, but it *must* be 
higher than the air temp or Ol' Stewball can't shed the heat as fast as 
its coming in.

The same applies to non-spherical horses, cars, dinosaurs, and all 
physical systems except graduate students.  Graduate students are, of 
course, capable of taking indefinite amounts of heat without producing 
anything at all for years at a time.

  --Toby White