heat transfer/ transfer of heat

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Is it the density of the metal (how heavy it is for a given mass) that affects a metal's ability to transfer heat within itself?

Like this, Say I take two frying pans. I connect them side-to-side via a plate of the same metal. I turn the stovetop on to heat one of them. How long will it take the other skillet to heat up and how hot will it get? What is this called and its properties?

Also, say after doing this experiment, I poured water in one of them. Once hot, would it, could it cool the other skillet by some form of ??????thermodynamics, convection, radiation, induction??????
 
There are 3 main modes of heat transfer: Conduction, Convection & Radiation. All 3 are in play with objects in an atmosphere. Convection does not exist in a vacuum, so only conduction and radiation are at play in space/vacuum.

In your example of two frying pans, the heat transfer between them will primarily be conduction through the plate between them.

https://www.google.com/#q=conduction+heat+transfer+explained

Quote:
Is it the density of the metal (how heavy it is for a given mass) that affects a metal's ability to transfer heat within itself?


It's the "thermal conductivity" of the material. Aluminum is less dense than lead, but it conducts heat 6 times better.

http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/thrcn.html#c1
 
It has something to do with how the electrons carry (conduct) heat.

Copper is a very good conductor. If you put one end into a fire, the other end will warm up in no time. Copper is also used for wiring.
 
In your sandwich of materials, the interfaces between them will limit the heat transfer, not the metal/alloy of each item. You can think of it as a resistive network, with the bulk materials having minimal resistance, and the gaps having something higher.

Because heat transfers based upon differences, you must also consider how much energy it takes to get an item hot. The heat capacity of aluminum is around 0.9J/g-C, while iron is 0.46 J/g-C. An ingot of the same mass will see vastly different bulk temperatures for the same amount of input energy. In a finished product, this may be different.
 
Originally Posted By: dlundblad
It has something to do with how the electrons carry (conduct) heat.

Copper is a very good conductor. If you put one end into a fire, the other end will warm up in no time. Copper is also used for wiring.



So, do you think if we were to put half of a piece of copper in ice water it would cool the other half just as fast as putting one end into a fire and it heating the other?


Do materials absorb heat at the same rate they expell it?
 
Originally Posted By: mjoekingz28

Do materials absorb heat at the same rate they expell it?


Thermal conductivity depends on the material, surface area and temperature differential. Then there is also thermal capacity, that is the amount of heat material absorbs before starting to expel the rest. The denser the material, the greater heat capacity, but slower absorption and rejection rates.

Problem with expelling heat is that the temperature differential on the cooling side is much, much lower than on the heating side. To solve this problem, the cooling side has to have a much greater surface area to compensate, hence we have cooling fins or radiators.
 
Originally Posted By: dlundblad
... Copper is a very good conductor. If you put one end into a fire, the other end will warm up in no time. Copper is also used for wiring.
... which brings up the point that metals generally rank about the same in thermal conductivity as they do in electrical conductivity. The time for your rod with one end in a fire to get hot at the other end depends not only on the material's conductivity, but also its density and specific heat.
 
Density has little to do with heat conductivity. Aluminum and copper were mentioned, and neither are particularly dense. You'll see stainless steel pots and pans with aluminum discs or copper bonded to the bottom to improve heat transfer. I've used steel cookware for backpacking, and it's not particularly good. It's mostly for weight savings. Titanium cookware is really not that great for cooking, but it's light.

I don't remember that much about my materials science classes, but I do remember that electrical conductivity has a lot to do with the availability of electrons. Basically any metal is going to be defined as having a sea of free electrons. The purity of the metal is also important. Impurities lead to "scattering sites" that keep electrons from taking the shortest route. Also, having a perfect crystal improves conductivity. A lot of copper wiring is sold as "high-conductivity oxygen-free" because it's been annealed at high temps in an oxygen-free environment. Annealing with oxygen will lead to oxygen impurities that tend to scatter electrons.

Here's an explanation:

Quote:
https://en.wikipedia.org/wiki/Thermal_conductivity#Influencing_factors

The effect of temperature on thermal conductivity is different for metals and nonmetals. In metals conductivity is primarily due to free electrons. Following the Wiedemann–Franz law, thermal conductivity of metals is approximately proportional to the absolute temperature (in kelvin) times electrical conductivity. In pure metals the electrical conductivity decreases with increasing temperature and thus the product of the two, the thermal conductivity, stays approximately constant. However, as temperatures approach absolute zero, the thermal conductivity decreases sharply. In alloys the change in electrical conductivity is usually smaller and thus thermal conductivity increases with temperature, often proportionally to temperature.
 
Originally Posted By: mjoekingz28
Originally Posted By: dlundblad
It has something to do with how the electrons carry (conduct) heat.

Copper is a very good conductor. If you put one end into a fire, the other end will warm up in no time. Copper is also used for wiring.



So, do you think if we were to put half of a piece of copper in ice water it would cool the other half just as fast as putting one end into a fire and it heating the other?


Do materials absorb heat at the same rate they expell it?


I would assume so, but I bet it'd act slower than placing the wire into the fire.

As for the second question, I am guessing this would depend how the part is allowed to heat up and then cool.
 
Originally Posted By: dlundblad
Originally Posted By: mjoekingz28

So, do you think if we were to put half of a piece of copper in ice water it would cool the other half just as fast as putting one end into a fire and it heating the other?


Do materials absorb heat at the same rate they expell it?


I would assume so, but I bet it'd act slower than placing the wire into the fire.

As for the second question, I am guessing this would depend how the part is allowed to heat up and then cool.


For a mind based example, If you had two tubs with a dry pocket in them for the ends of the wire to sit in.

Fill one of the tubs with Ice water, and the other tub with a supply of saturated steam (constant 0C and 100C heat sink/source) then energy will flow from hot to cold. Empty the ice water, and replace it with some other fluid with a constant 200C, and again, the same thing will happen.

Same amount of heat will flow, just the other way.

Take a penny at 50C and drop it in ice water, and a measure of heat will be lost. Same 50C penny in a steam bath at 100C will pick up the same amount of heat getting from 50C to 100C as it lost going 50C to 0C...drop it into the ice water, and it will lose TWO measures of heat energy going from 100C to 0C.

Those are mind games.

When you get into actual heat transfer, there's radiative, which depends on the emissivity of the two components and the difference in their temperatures T^4-t^4 (T being the hottest temperture in Kelvin, t the lowest). Convection on the difference in temperture, and conduction on difference, and nature of contact...much more tricky.
 
Originally Posted By: mjoekingz28
How come the handle on my cast iron skillet doesnt get near as hot as the rest of it?


Usually the skillet is not on the heat long enough for the handle to get hot , when you consider the following.
Generally the food in the pan helps dissipate heat, sometimes in the form of steam. Most cast iron skillets/pan handles have a hole in them to dissipate heat.

Leave a skillet on enough heat long enough with nothing to dissipate the heat and the handle will get very hot( the skillet may crack too).
 
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