[bizerl (OP)]

When trying out my new stainless steel frypans, I noticed they heat up and cool down much faster than my old ones. Is there a measureable speed at which heat radiates through a material, and what is the quality of the material that would influence such a speed?

[Geezer]

The rate at which heat travels through metals is known as thermal conduction. For metals, their ability to conduct heat is similar to their ability to conduct electricity. For example, aluminium and copper are both good electrical and thermal conductors.

[Bored chemist]

Not quite.
The speed at which a change in temperature moves through something is related to the thermal diffusivity. It is possible to have two objects with the same thermal conductivity but for heat to travel faster through one than the other.
http://en.wikipedia.org/wiki/Thermal_diffusivity

[Geezer]

Rats! Another gap in my education.

[evan_au]

The thickness of the material also matters; thinner=faster to heat up.

Some pans have a copper core, and will heat up more quickly & evenly - but these cost more, so I would expect it to be clearly stated on the label...

[chris]

To rub some ointment on Geezer's wounds and to add a little extra clarification, as Geezer has highlighted, in general the reason why metals tend to be good conductors of heat - as well as electricity - is down to their crystal structure.

Metals are considered to be a lattice of positive ions (nuclei) in a sea of electrons. These electrons can move freely, swapping between the different positive centres. As Chemistry World science writer Mike Brown eloquently put it to me, "you can think of it like a troop of atomic jugglers - the metal nuclei - lobbing skittles (electrons) back and forth amongst themselves."

The consequence is that, when a metal is heated, the kinetic energy (vibrations) of the electrons increases. And because they are free to move, they can collide with other particles (both electrons and ions) over greater distances and transmit these vibrations through the material, which is why heat is well conducted.

The freedom of the electrons to move also accounts for the high electrical conductivity. Ionic materials, where the electrons are not free to move in this way, tend to be poorer conductors as a consequence.

Someone else can explain why graphite has the conduction properties that it does.

Chris

[Bored chemist]

Never mind graphite, how do you explain diamond?
It's a very good conductor of heat, but it can't be because of a sea of moving electrons because diamond is an excellent electrical insulator- there are no free electrons.
(BeO and a few other materials have the same property)

[chris]

Indeed - my brain exploded before I could even begin to think about how to explain that! What do people think might be going on in diamond?

[Bored chemist]

Well, Wiki says this
http://en.wikipedia.org/wiki/Thermal_conductivity#Lattice_waves
but I'm not convinced.
We all know that the phonons were the "villains" in an obscure Dr Who episode in the mid 1970s.

[evan_au]

In a very hard material such as diamond, the speed of sound can be very high. Heat is just vibrations of the atoms, and this can travel at a similar speed.

Diamond is made up of several isotopes of carbon. Using isotopically pure carbon increases its thermal conductivity - said to be the highest of any material.
http://en.wikipedia.org/wiki/Material_properties_of_diamond#Thermal_conductivity

Presumably the varying isotopic concentrations of natural diamond scatter and diffract the phonons as they pass through the crystal, just like crystal boundaries and impurities do in other materials.

Heat pipes also work quite well, but they use boiling and condensation to transfer the heat, so they only work over a very narrow range of temperatures. Because they rely on physical movement of a vapour, the velocity of heat transfer is fairly low.
http://en.wikipedia.org/wiki/Heat_pipes

[evan_au]

We feel Infra-Red radiation as heat, and this travels at the speed of light.

Of course, in a material transparent to IR, the speed of light is somewhat less than it's usual value in a vacuum - but a photon beats a phonon!

[William McCormick]

Never mind graphite, how do you explain diamond?
It's a very good conductor of heat, but it can't be because of a sea of moving electrons because diamond is an excellent electrical insulator- there are no free electrons.
(BeO and a few other materials have the same property)

Diamonds are an amazing substance. Diamonds actually change the emission of heat to some other form of emission. I have never had the time or the equipment to tell you exactly what that emission is. However it was taught to me, that way by a master machinist. I believe there are even a few more modern scientists that have also confirmed this. Engineers in the electrical field, have also used diamonds in this way to remove heat from electrical components. It is documented but only in obscure pamphlets.

Years ago they used to use a phosphorous compound to harden metal. It worked by altering the emission from hot glowing metal to be hardened, from a heat emission to a light emission. It glowed white hot when it was applied to the red metal to be hardened. It worked extremely well. Phosphorous is an extreme poison, that may have lead to it being taken off the market.

Light removes much more energy from a part, then heat. You can kind of witness this, when you light a light bulb, with low voltage, or under voltage, it glows red. When you raise the voltage it glows yellow or nearly white or blue. Showing you which emission removes more energy. It actually uses velocity as the principle, but I am new to the forum and I do not want to rock too many boats.

The phosphorous hardening compound works in a similar way, instead of raising the amount of energy in the part, you offer the energy, a very exited path to drain the energy or abundance of particles in the part, very quickly.

The direction of heat as was mentioned makes a very big difference, by heating a part halfway between the two ends of the part, it makes it possible to heat one end much more quickly, and even limit the heat that makes it to the cold end of the part. When you heat the center of the part, you send heat out towards the end you want to heat. By the time the heat from the end you are trying to heat, can reverse the flow, of the heat moving towards it. The end you are heating heats up without being able to transfer the heat to the rest of the part.

It is an old welders trick to weld a part that is to big to just weld with the equipment you have.

If you dip the heated end, of a piece of aluminum that is heated on one end by welding process, or bending process, into a bucket of water very quickly, the heat will move very quickly towards the cold end of the aluminum, enough to burn your hand in seconds of quenching. Yet on the same part heated the same way but not quenched, the cold end will not even get hot, before it cools in air. To me that is a phenomena.

Some stainless pans have an aluminum disk inside the pan. It is manufactured inside the stainless pans bottom. To keep the heat even in the pan and to speed the heating of the pan.


                      Sincerely,

                            William McCormick

[damocles]

Diamond is not alone in being a non-conductor with very high thermal conductivity and diffusivity. The alkali metal oxides, lime, magnesia, and beryllium oxide are other examples from many (and they are much cheaper and more practical than diamond!

Beryllium oxide is favoured as the ideal heat sink because it has a large heat capacity to go along with its high conductivity and diffusivity. Unfortunately it is a very dangerous substance to handle. Magnesia (magnesium oxide) is nearly as good.

[Bored chemist]

I think the problem with William McCormick's post is that it's essentially nonsense.
Fro example, while he writes that "Light removes much more energy from a part, then heat."
In fact about 3% of the power supplied to a light bulb is dissipated as light. The other 97% is lost as heat.
Heat removes about  33 times more energy in this case than light does.
If you reduce the voltage then the re comes a point where the filament is too cool to emit light, but it still gives heat.
In this case light is utterly incapable of removing energy from the filament, but heat still does it just fine.

Phosphorus compounds are still used in hardening some steels, but the effect is due to interstitial pinning of the lattice- nothing to do with light emission.

[William McCormick]

Heat does not travel far. Infrared does. Are you saying that infrared is heat, and not light?

It really is neither. Infrared red light, will pass through an opaque raw computer chip wafer, without heating the wafer, making it seem not at all like heat. It will heat flesh just on the other side of the wafer though. Much like you would expect light to do after passing through a glass window. So perhaps we just have to agree on what infrared is?

When you raise the voltage to a light bulb, it can no longer just give off heat, to remove energy, heat is no longer capable of removing the abundance of energy in the filament. The filament in a quest to remain a filament, starts to emit light and infrared heat. As well as UV, and even X-rays as the light gets brighter and brighter, before it destroys itself. You can only put a few watts to a light bulb before it gives off light.

Our sun is a giant carbon laser, it is white if viewed outside of our atmosphere, the only reason that heat from the sun reaches us, is because it travels as light, UV, and of course X-rays. Those rays can penetrate just about any single wall material we try to block them with, after you leave the earths atmosphere.

Heat does not travel in a vacuum well, because there are so few air particles to transfer the actual heat. A light bulb transmits energy by way of light, and infrared.

If they are currently measuring this in some other way, or calling infrared, heat, I would love to hear about it.

                      Sincerely,

                            William McCormick

[Bored chemist]

Please don't waste the forum's bandwidth with gibberish like "Our sun is a giant carbon laser"

You may also want to look at this
http://en.wikipedia.org/wiki/Radiant_heating
Radiant heat does exist.

"When you raise the voltage to a light bulb, it can no longer just give off heat, to remove energy, heat is no longer capable of removing the abundance of energy in the filament. " is still nonsense
Most of the energy lost from the filament is lost as heat.

[William McCormick]

So you are saying that infrared light, is classified as heat not light?

True radiant heat is infrared at a certain frequency or wave length. It works very much like light. An infrared emitter is used. The heaters in the Quiznos sandwich ovens are infrared.

The terminology in the field of building and for use by the homeowner is often vague and unscientific. A standard hydronic radiator, mounted at the base of a wall, called base board heat, in a home. Is usually powered by a gas or oil burning system, that heats water that is circulated through pipes to the base board heat. Sometimes solar or electric heat, is used to heat hot water for the baseboard heater.

The baseboard radiator, does not actually radiate much at all, rather it, is a convection device. Air has to pass over aluminum fins to transfer the heat to the air.

The hydrocnic hot water heated floor system, is also called radiant heat, however again it uses convection to take the heat from the floor and heat the rest of the room. They basically lay PEX tubing, Cross-linked polyethylene, commonly abbreviated PEX or XLPE, in the floor up and down the length of the floor. They run hot water through it.

The sun is surrounded by carbon dioxide, it has been printed in books of learning for many years that way. What do they say it is now? Would you like me dig some of them up?
 


                      Sincerely,

                            William McCormick

[William McCormick]

The heaters in the Quiznos ovens are just filaments surrounded by pure silicon. The rays pass through the silicon and heat the sandwich. Silicon is such a good insulator against heat, that is how we know that it is infrared passing through the silicon, not just heat.

                      Sincerely,

                            William McCormick 

[Bored chemist]

"So you are saying that infrared light, is classified as heat not light?"
yes, so is that wiki page; and so do you.
"True radiant heat is infrared at a certain frequency or wave length."

I know that most so called "radiators" actually transfer heat by convection and advection, but that's nothing to do with the fact that you were wrong to say that light transfers more heat. In the great majority of cases the reverse is true by a big margin.

Silicon is actually quite a good conductor of heat and, especially when it is hot, a good conductor of electricity too so I rather doubt that "The heaters in the Quiznos ovens are just filaments surrounded by pure silicon."
However because there's no easy way for me to check on  some particular sandwich seller's equipment in another country I can't be certain.

However if you mean that they are surrounded by silica (like these ones)
http://en.wikipedia.org/wiki/Infrared_heater#Quartz_heat_lamps
that's another matter.
Some thing like Quinzo's which isn't accessible to 95% of the world's population isn't a good choice of example.

Silica is a reasonably good conductor of heat anyway, so your point isn't valid.

And this "The sun is surrounded by carbon dioxide, it has been printed in books of learning for many years that way. What do they say it is now? Would you like me dig some of them up?"
is just bollocks.

The sun is surrounded by the corona, the solar wind and a vacuum.
Not only are those in fact made largely of hydrogen, but any CO2 there would get destroyed by the high temperature.

I can't imagine where you got such a silly idea as that the sun is surrounded by CO2.

[William McCormick]

I believe what I said is highly accurate, for the purpose I said it. Light is necessary to create the infrared emission from the element. You just cannot do it without the light. Meaning as you increase the power to the element, it naturally starts emitting rays designed to carry away more energy. And they do.

When I create a very powerful ARC through pure argon, using a couple thousand watts, of power, there is a pinpoint heat generated, in very close proximity to the ARC,  however most of the rays, leave the area, as light and UV.  There is almost no infrared. So I have to contest that heat is reliving the area of energy.

Regular heat does not pass through silicon without heating it, infrared rays do. Now I was taught that infrared is a form of light. It certainly is not regular heat.

On the other side of the coin infrared is ineffective at moving the veins of a radiometer, if no white light is present. If there is the slightest white light present, then the infrared will move the veins of the radiometer and at amazing speeds.

Certainly the terminology leaves something to be desired of no matter which way you look at it. I don't think that infrared is neither light or heat myself. But I do not see why we cannot make communication about it better.

                      Sincerely,

                            William McCormick