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Old 01-03-2006, 06:49 AM posted to
Bob (this one) Bob (this one) is offline
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Default Baking cakes in foil pans

Bob (this one) wrote:
s foil pans reflect heat.

I did as you suggested. *All* the hits were from non-scientific sites,
with the words sounding like they were written by the same person. You
need to evaluate the sources of your information better than you did.
None were authoritative, and merely parroted each other.

Now look at the technical sites...

"If metal is a conductor of heat, why is it that aluminum foil will
insulate food and reflect heat?
"Aluminum may be a good conductor of heat, but its a terrible
emitter or absorber of thermal radiation. When you wrap food in aluminum
foil, you dramatically reduce that food's ability to lose heat via
radiation if it's hotter than its surroundings or its ability to gain
heat via radiation if it's colder than its surroundings. Aluminum foil
doesn't have much effect on heat transferred to or from the food via
conduction or convection because aluminum itself is a good conductor of

"...terrible emitter or absorber of thermal radiation" means that it
doesn't reflect it, it simply doesn't absorb it. It doesn't make it go
back where it came from, nor does it capture it.

See that "good conductor of heat" thing? Not "reflector" of heat.

Here's another one:
"2.132 Reflect radiant heat waves
Heat tissue paper with a magnifying glass, as in 2.131. Note the
distance from the reading glass to the tissue paper. Put a tilted mirror
half way between the lens and the paper. Feel with your hand above the
mirror until you find the point where the heat waves are focussed. Hold
a piece of paper tissue at this point. The paper ignites."

That wouldn't happen in the dark. Light is radiant heat. It reflects
light. It doesn't reflect heat as heat, it just doesn't absorb radiant
energy well, nor does it transmit it. You say it reflects heat, so I'm
sure you'd closely wrap your hand in a single layer of foil and hold a
candle under it such that the flame was 1/2 inch below it. It'll reflect
the radiant heat (we call that light) but the conducted heat and
convected heat will fricassee your hand. That's why aluminum cookware
works well. It conducts heat very well; it doesn't reflect it back
towards the flame or the coil.

"23.00 Heat & temperature, internal energy & heat, heat and the first
law of thermodynamics
Heat is a form of energy measured in Joule. The first law of
thermodynamics states when other forms of energy are converted to heat,
or when heat is converted to other forms of energy, there is no loss of
total energy. The second law of thermodynamics states heat always flows
from hot bodies to cold bodies. "

Note that aluminum is right behind gold and copper in its capacity to
conduct heat (the last column of the chart). Silver isn't mentioned, but
it's at the top of the list.

"Clearly in selecting a conductor these are very significant differences
- so the best materials are those which lie low towards the bottom of
the metals bubble, such as copper and aluminium. Gold is excellent, but
it is so expensive it is way off the scale of the chart. Even so, it is
used for electrical contacts in microcircuits.

"Finally, thermal conductivity and electrical conductivity are closely
related - as the underlying physics is similar. The electrical
resistivity chart also gives an indication of thermal properties - with
thermal insulators towards the top (polymers and foams, and ceramics)
and the good thermal conductors - metals - at the bottom."

This means that heat and electricity are treated similarly by metals.
Aluminum is a good conductor of electricity, so it's also a good
conductor of heat. As nothing reflects electricity, nothing reflects
heat, either.

You might want to consider why there are charts for conduction of heat,
but none for reflection of heat.

This whole issue reminds me of that silly device with a hemispherical
mirror (like a bowl) into which you were supposed to put ice to reflect
the cold upwards and chill things in a small basket at the mouth of the
bowl. It was a physical impossibility.

Now you go find out what "heat" is and is not. And learn the difference
between radiant heat and conducted or convected heat is. And don't go to
cooking hobbyist sites for lessons in physics.


You can quote as much so called

Hey, moron. This kind of sneering dismissal of researched and documented
information marks you for an ignorant fool. When there's data from
several reliable sources and you say, "Oh, no, I know better," you end
up looking like a blowhole driven by ego and the obviously mistaken
belief that it's correct just because you believe it.

scientific proof

Yes. Scientific proof. As opposed to your confused ramblings that show
you have no idea about heat, its movement and reflectivity.

as much as you want
but I know from experience that shiny aluminum baking pans reflect

So you say. And you *know* it's reflecting heat rather than simply not
transmitting it. What a wonderful thermal effects laboratory you must have.

LOL You *know* what's happening, and then you offer the stuff below as
"proof." Hilarious.

Besides, there's a big difference between the way a pan heats up
on a stove and the way a pan heats up in an oven. A pan on a stove
heats up entirely by conduction.

So the red glow from the electric coil isn't radiant heat. And the very
visible gas flame isn't radiant heat. Got it. I bet your physics teacher
is proud of you.

I bet that's why you're perfectly happy to hold your hand right next to
the pan while it cooks. No radiant heat means none released to the air,

A pan in an oven heats up by means of
radiation and indirect conduction, that is the oven's heat source heats
the air inside the oven and the heat from the air is conducted into the

There's no such thing as "indirect conduction." Heat is either conducted
or it isn't. There's a grand total of three ways for heat to move -
radiation, conduction, convection. There's no "indirect" way for heat to

Since light colored materials reflect radiant energy,

Um, *visible* radiant energy and infra-red. The energy radiating from
hot oven walls isn't visible; too far down on the electromagnetic
spectrum (You do know what that is, right?). That light-colored business
refers to "albedo." And you need to learn the difference between
"shiny" and "light-colored."

part of the
radiant heat inside the oven is reflected away from the pan.

You didn't read anything from those science sites at all, did you...?

Like it says above: "You might want to consider why there are charts for
conduction of heat, but none for reflection of heat."

We're done with this. You haven't the remotest idea what you're talking
about. The very simple fact is that you're wrong. The next fact is that
you aren't interested in learning. You're over your head with this subject.

For future reference, one person's anecdotal experience is *never* proof
of an assertion. Not yours, not mine.