NetNews Usenet Archive 1993 #1/NN_1993_1.iso/spool/sci/electron/22143

Internet Message Format | 1993-01-06 | 5.5 KB

Xref: sparky sci.electronics:22143 sci.energy:6690 rec.autos:31124
Path: sparky!uunet!spool.mu.edu!olivea!apple!goofy!mumbo.apple.com!michael.apple.com!ems
From: [e-mail] (E. Michael Smith)
Newsgroups: sci.electronics,sci.energy,rec.autos
Subject: Heat vs. Temperature?  Re: Flywheel batteries as EV power source
Message-ID: <[e-mail]>
Date: 28 Dec 92 20:42:06 GMT
References: <[e-mail]> <[e-mail]> <[e-mail]>
Organization: Circle 'C' Shellfish Ranch, Shores-of-the-Pacific, California
Lines: 96

I think that maybe, to some extent, the two of you are arguing about
heat vs temperature ...  Yes, all the energy degrades to heat, but
some of that heat goes into things like phase changes that do not
require that all the heat be reflected as higher temperature...

I, personally, think the quantities of heat being dealt with are such
that the temperature reached will be that of plasma, in any case, with
the attendent pressures...
.
Perhaps you could both state clearly when you mean heat and when you
mean temperature?

In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>In article <[e-mail]> () writes:
>>In article <[e-mail]>, [e-mail] (Richard Stead) writes:
>>>
>>> In article <[e-mail]>,  writes:
>>> > In article <[e-mail]>, [e-mail] (Richard Stead) writes:
>>> the way the molecules work is that you
>>> must do work against the molecules to separate them, but once separated,
>>> they snap back, releasing the acculmulated strain energy as heat.  That's
>>> right, energy is conserved, and a pile of shredded composite does not
>>> represent more energy than the whole piece.  Entropy simply means that
>>> energy has been converted to heat.

SOME of which shows up as temperature increase.

>>Unfortunately wrong, and very sloppy.  Take a ream of paper and turn it into
>>scraps and tell me you haven't expended energy.  That energy came from the
>>flywheel hense the fluff does not have the same energy as the initial flywheel.
>Sorry wrong. If you tear a ream of paper into shreds, the chemical potential
>energy in your body has been converted to mechanical energy which degrades
>to heat, both in your inefficient muscles and in the torn paper. Now the
>paper doesn't get very hot, but that's because you don't have to expend
>much energy tearing paper. Try taking a wire coathanger and bending it
>back and forth until it breaks. Both you and it will get hot. With the
>flywheel, there's an enormous amount of energy released in a very short
>time. None of that energy can leave the system until the containment
>ruptures. *All* of it degrades to heat, megajoules of heat, equivalent
>to about 200 pounds of dynamite.

This example freely intermixes heat and temperature effects...

>>Energy has been used bending molecules, which may or may not snap back, but
>>more significantly in breaking bonds which originally held the flywheel
>>together.  Now if you've got the inter fiber bond strength of a material of
>>carbon carbon fibers we could use for a fly wheel, your a hell of a lot
>>farther ahead that most in the carbon carbon field.  Now is this energy enough
>>to make the fluff safe, I don't know, that's why I asked.  Remember that
>>carbon carbon bonds are one of the strongest bonds around, thats why we
>>want to use carbon carbon in the first place.

This arguement seems to be that the heat will, in large enough measure
to prevent catastophic temperature excursions, be converted to some
non-temperature form (chemical bonds, or the lack thereof, strain, etc.)

Somehow I doubt that this is possible, given the magnitude of energy.

>>> I repeat for the billionth time, energy is conserved!
>>
>>Can't you listen to your own point?
>
>You are the one who doesn't understand. It's a closed system. All the
>energy originally contained in the flywheel degrades to heat if kinetic
>particles don't penetrate the housing and escape immediately. Breaking
>a chemical bond takes energy, but that energy doesn't disappear when
>the bond breaks. It reappears as kinetic rebound in the component atoms.
>Another term for kinetic motion of atoms is *heat*. *All* the energy in
>the flywheel degrades to heat, and it happens in microseconds. Releasing
>8 MJ of energy in microseconds is called an explosion. A damn big one.

This seems to confound heat and temperature.  Yes, the heat is conserved,
but if you have changed the chemical composition and/or phase, you have
also changed things like the specific heat of the compounds involved
and/or soaked up heat in things like phase changes that do not reflect
that energy as temperature.  Not all heat put into breaking chemical
bonds shows up as higher temperature.  If you think otherwise, disolve
some salts in water and see what happens.  Ammonia salts are fun ...

Is it enough to prevent an explosion?  I doubt it...

>You'd do well to study thermodynamics and quantum chemistry before you
>flame someone about something you don't understand.

And all of you would be better served by putting numbers on things
and by being very carefull about the difference between heat and
temperature...

--

E. Michael Smith  [e-mail]

'Whatever you can do, or dream you can, begin it.  Boldness has
 genius, power and magic in it.'  -  Goethe

I am not responsible nor is anyone else.  Everything is disclaimed.