Tuesday, February 14, 2012

It's a Krammie

A while ago Eli asked "What is heat" inspired by the new ridiculous most recently shredded at Science of Doom, and got some decent answers. DeWitt did some reading

You might want to check out John Denker's take on thermodynamics

"The term "heat" is a confusing chimera. It is partly energy, partly entropy, partly temperature, and partly who-knows-what. It shows up in a variety of idiomatic expressions, as discussed in section 16.2.

By itself, the word "heat" has at least five sensible and widely-used but mutually-inconsistent technical meanings (not to mention innumerable nontechnical and metaphorical meanings). It is not worth arguing about the relative merits of these meanings, except to say that each has some merit. I observe that a typical thoughtful expert will use each of these meanings, depending on context. It would be nice to have a single, universally-accepted meaning, but I doubt that will happen anytime soon."
Thad provided the wisdom of Count Rumford, a traitor, scoundrel, womanizer and arms dealer, John went to the text books
Heat is not the same as "Thermal Energy:"
Thermal energy is energy that a body has by virtue of being at a temperature T > 0K.
Heat is thermal energy that is in motion from one body to another.
So (for example) if a body is at a temperature of 500 C, and the metal is surrounded by a layer of perfect insulation, then the body has thermal energy, but no heat. Because the thermal energy isn't flowing from one body to another.
to which Eli replied
John, while that is fairly standard, as John Donne Rabett said,
No body is an island
No energy stands alone
Each body can be subdivided
Into more bodies
In which internally heat is flown

That definition gets you into the issue of where is the system and where is the surroundings which is arbitrary. For example take a chunk of metal and heat a small part of it. Heat flows within the chunk.

Moreover, even in an isothermal body, energy is flowing from one part to the other, in balance, but there are fluctuations which can be used for some purposes such as random noise generation.
Of course, the nonsense has its roots in Mama Nonsense, Gerlich and Tsch. who try and define radiation exchange as something else (e.g. they claim that the only heat flow is the net, which means that the thermal radiation (aka heat) flowing from the colder to the hotter body ain't heat, so since this warms the surface, blah, blah.

The same issue came up at the Weasel's, and the renter was not amused. Eli's response was

The argument depends on deceptively and incorrectly manipulating the definition of heat. As far as energy goes there is heat and everything else. Everything else can be converted to work with unit efficiency, heat conversion to work is limited by the second law.

It's a Krammie.

but Martin wins

But William, Your Eminence, what you're both missing is that that downwelling radiation doesn't actually warm anything. It's just informational. Those photons are gathering in Internet cafes around the planet, writing intellectually dense blog comments...

[Aieeee, my brain has started hurting :-). I need to keep a link to “Blah blah blah” vs Equations handy -W]


carrot eater said...

bah. flow of thermal energy. within a body, between bodies, doesn't matter.

but the dynamic equilibrium within your isothermal body need not apply. got to draw the semantic line somewhere.

VeryTallGuy said...

Popcorn anyone ?