Aluminium foil

[Nithin]

Why doesn't aluminium foil get too hot to touch in the oven? Is it too thin to hold heat? Would this be true of any foil?

 

[Turkish]

i would like to know this as well. good question.

 

[MrThermistor]

It gets just as hot as anything else, but the rush of air from opening the oven cools it quickly.

Try opening the oven just a crack and reaching in to touch.

 

[RossGr]

Al foil does get hot, it is just that the specific heat of Al is low, that combined with the low amount of material (small mass) foil does not contain enough heat energy to burn you. When you touch the foil it quickly adjusts to the temperature of your fingers, thus does not seem hot. If you have a larger (more massive) piece of Al you can certainly burn yourself.

 

[Red Squirrel]

Also, aluminum has a better heat conductivity so the heat probably "gets off" faster when taken out of the oven. But I assume the main factor is what has already been mentioned, that's it's thin. (hence why heatsinks have "Fins" instead of just being a big block)

 

[Mday]

Originally posted by: Nithin
Why doesn't aluminium foil get too hot to touch in the oven? Is it too thin to hold heat? Would this be true of any foil?

it does get hot. the foil is so thin that it's surface area relative to it's size is HUGE, so it cools off fast.

 

[blahblah99]

Originally posted by: Mday

Originally posted by: Nithin
Why doesn't aluminium foil get too hot to touch in the oven? Is it too thin to hold heat? Would this be true of any foil?

it does get hot. the foil is so thin that it's surface area relative to it's size is HUGE, so it cools off fast.

Yup. Surface area to mass ratio is humungous.

 

[DrPizza]

I agree that the surface area is huge compared to the volume, but the effect is due to the specific heat of aluminum, rather than the rate of cooling. There just isn't enough heat in the volume of aluminum that you're grabbing to burn you.

 

[gururu]

There just isn't enough heat in the volume of aluminum that you're grabbing to burn you.

that can be misleading though, because if the thin sheet of aluminum is acting as a conduit between a heat source and your finger, you'll get burned. Also, if the aluminum is heated to 2000 degrees (or its highest temperature as a solid), then even the small amount of aluminum will burn you. Aluminum right out of the oven can burn. It is just that it cools off before you touch it as others have described.

 

[RossGr]

Originally posted by: gururu

There just isn't enough heat in the volume of aluminum that you're grabbing to burn you.

that can be misleading though, because if the thin sheet of aluminum is acting as a conduit between a heat source and your finger, you'll get burned. Also, if the aluminum is heated to 2000 degrees (or its highest temperature as a solid), then even the small amount of aluminum will burn you. Aluminum right out of the oven can burn. It is just that it cools off before you touch it as others have described.

You need to check some references the melting pt of Al is 660C or 1220F. I thought this thread was about Al Foil , not moltan Al?

Remember that the amount of heat conducted depents on the cross sectional area of the conductor so foil cus it is soooo thin really does not conduct a lot of heat.

Next experiment, aquire some thin SS shim stock, throw in oven at 350F along with the same size piece of Al foil, Pick it up one in each hand and describe the sensation you feel in your finger tips. The SS (Thats Stainless Steel) will burn your fingers the Al will not. I repeat SPECIFIC HEAT is the root cause.

 

[ZeroNine8]

Originally posted by: RossGr<br

Next experiment, aquire some thin SS shim stock, throw in oven at 350F along with the same size piece of Al foil, Pick it up one in each hand and describe the sensation you feel in your finger tips. The SS (Thats Stainless Steel) will burn your fingers the Al will not. I repeat SPECIFIC HEAT is the root cause.

About the fact that the stainless steel will be more likely to burn you, correct. About your assertion that it is due to specific heat of aluminum vs steel, you are 100% wrong (check your facts next time).

The specific heat of several Stainless Steel and Aluminum Alloys are given below in Btu/lb-F

Stainless 316______0.12
Stainless 440______0.11
Aluminum 1100_____0.216
Aluminum 6061_____0.214
Aluminum 7075_____0.23

As you can see, aluminum alloys have almost twice the specific heat, or energy (Btu) per unit mass, of stainless steel alloys.

Why does the stainless steel have more energy to 'burn' you when heated then? Simple, density. Below are densities of the same alloys in lb/in^3

Stainless 316_____0.284
Stainless 440_____0.279
Aluminum 1100____0.098
Aluminum 6061____0.098
Aluminum 7075____0.101

Here you see that stainless steel is approaching 3x the density of aluminum. So for the same sized (volume) piece of material, as you proposed, the resulting energy of each piece of the same volume is (in units of Btu/in^3-F)

Stainless 316_____0.03408
Stainless 440_____0.03069
Aluminum 1100____0.021168
Aluminum 6061____0.020972
Aluminum 7075____0.02323

Now you see that stainless steel pieces of the same geometric size will contain about 150% of the thermal energy of aluminum pieces at the same temperature.

And the reason foil doesn't burn you coming out of the oven is due to the fact that it is so thin (as was stated several times already) that relatively little thermal energy is stored and it tends to cool off very quickly either in the air or by touch.

edited for formatting

 

[DrPizza]

Originally posted by: ZeroNine8

Originally posted by: RossGr<br

Next experiment, aquire some thin SS shim stock, throw in oven at 350F along with the same size piece of Al foil, Pick it up one in each hand and describe the sensation you feel in your finger tips. The SS (Thats Stainless Steel) will burn your fingers the Al will not. I repeat SPECIFIC HEAT is the root cause.

About the fact that the stainless steel will be more likely to burn you, correct. About your assertion that it is due to specific heat of aluminum vs steel, you are 100% wrong (check your facts next time).

The specific heat of several Stainless Steel and Aluminum Alloys are given below in Btu/lb-F

Stainless 316______0.12
Stainless 440______0.11
Aluminum 1100_____0.216
Aluminum 6061_____0.214
Aluminum 7075_____0.23

As you can see, aluminum alloys have almost twice the specific heat, or energy (Btu) per unit mass, of stainless steel alloys.

Why does the stainless steel have more energy to 'burn' you when heated then? Simple, density. Below are densities of the same alloys in lb/in^2

Stainless 316_____0.284
Stainless 440_____0.279
Aluminum 1100____0.098
Aluminum 6061____0.098
Aluminum 7075____0.101

Here you see that stainless steel is approaching 3x the density of aluminum. So for the same sized (volume) piece of material, as you proposed, the resulting energy of each piece of the same volume is (in units of Btu/in^2-F)

Stainless 316_____0.03408
Stainless 440_____0.03069
Aluminum 1100____0.021168
Aluminum 6061____0.020972
Aluminum 7075____0.02323

Now you see that stainless steel pieces of the same geometric size will contain about 150% of the thermal energy of aluminum pieces at the same temperature.

And the reason foil doesn't burn you coming out of the oven is due to the fact that it is so thin (as was stated several times already) that relatively little thermal energy is stored and it tends to cool off very quickly either in the air or by touch.

edited for formatting

Excellent point. The specific heat is the amount of heat needed to raise 1 gram of a substance by 1 degree celsius. The specific heat of steel is lower, meaning it needs less energy to heat it for each degree (for the same amount of mass) as aluminum. Thus foil made out of steel would contain less energy than aluminum foil (of the same size and thickness) and would burn your hand even less. Nonetheless, the specific heat of the substance, along with the mass and temperature of the substance determines how much heat is present to burn your fingers. Thus, your assertion that specific heat is 100% wrong is also wrong.

The actual answer is: Low mass and relatively low specific heat are the reasons your fingers don't get burnt. If you could touch the same mass of water with your fingers, at the same temperature (which likely means steam), your fingers will get burnt... (steam holds about 2 1/2 times as much energy gram for gram as aluminum, water holds about 5 times as much. plus there's the energy it took to boil the water.)

 

[ZeroNine8]

Originally posted by: DrPizza

Excellent point. The specific heat is the amount of heat needed to raise 1 gram of a substance by 1 degree celsius. The specific heat of steel is lower, meaning it needs less energy to heat it for each degree (for the same amount of mass) as aluminum. Thus foil made out of steel would contain less energy than aluminum foil (of the same size and thickness) and would burn your hand even less. Nonetheless, the specific heat of the substance, along with the mass and temperature of the substance determines how much heat is present to burn your fingers. Thus, your assertion that specific heat is 100% wrong is also wrong.

The actual answer is: Low mass and relatively low specific heat are the reasons your fingers don't get burnt. If you could touch the same mass of water with your fingers, at the same temperature (which likely means steam), your fingers will get burnt... (steam holds about 2 1/2 times as much energy gram for gram as aluminum, water holds about 5 times as much. plus there's the energy it took to boil the water.)

You have some flaws in this logic that I will point out individually with explanation.

The specific heat is the amount of heat needed to raise 1 gram of a substance by 1 degree celsius. The specific heat of steel is lower, meaning it needs less energy to heat it for each degree (for the same amount of mass) as aluminum.

Yes.

Thus foil made out of steel would contain less energy than aluminum foil (of the same size and thickness) and would burn your hand even less.

No, foil made out of steel would contain less energy than aluminum foil (OF THE SAME MASS). Because of differing density, steel foil and aluminum foil of the same size and thickness would have different mass and, consequently, different amounts of energy at the same temperature. (I discuss this density effect in the third set of numbers presented)

Nonetheless, the specific heat of the substance, along with the mass and temperature of the substance determines how much heat is present to burn your fingers.

Yes, exactly what I said in the third part of my post:

Here you see that stainless steel is approaching 3x the density of aluminum. So for the same sized (volume) piece of material, as you proposed, the resulting energy of each piece of the same volume is (in units of Btu/in^3-F)

Stainless 316_____0.03408
Stainless 440_____0.03069
Aluminum 1100____0.021168
Aluminum 6061____0.020972
Aluminum 7075____0.02323

Now you see that stainless steel pieces of the same geometric size will contain about 150% of the thermal energy of aluminum pieces at the same temperature.

Unless my calculations are wrong, I don't see how you can conclude anything else from this data. This is the energy stored per unit volume per degree, which is exactly corresponding to the 'size' and 'thickness' you speak of.

Thus, your assertion that specific heat is 100% wrong is also wrong.

I don't see how, since I clearly showed that while having a higher specific heat, aluminum foil contains less energy than steel of the same dimension due to DENSITY. If it were determined by specific heat, the aluminum would have more energy, thus be more likely to burn, which is not the case.

The actual answer is: Low mass and relatively low specific heat are the reasons your fingers don't get burnt. If you could touch the same mass of water with your fingers, at the same temperature (which likely means steam), your fingers will get burnt... (steam holds about 2 1/2 times as much energy gram for gram as aluminum, water holds about 5 times as much. plus there's the energy it took to boil the water.)

Agreed, this is basically a restatement of 'it is thin and doesn't store much energy' that seems to be the consensus of why foil doesn't burn you.

 

[DrPizza]

Originally posted by: ZeroNine8

Originally posted by: DrPizza

Excellent point. The specific heat is the amount of heat needed to raise 1 gram of a substance by 1 degree celsius. The specific heat of steel is lower, meaning it needs less energy to heat it for each degree (for the same amount of mass) as aluminum. Thus foil made out of steel would contain less energy than aluminum foil (of the same size and thickness) and would burn your hand even less. Nonetheless, the specific heat of the substance, along with the mass and temperature of the substance determines how much heat is present to burn your fingers. Thus, your assertion that specific heat is 100% wrong is also wrong.

The actual answer is: Low mass and relatively low specific heat are the reasons your fingers don't get burnt. If you could touch the same mass of water with your fingers, at the same temperature (which likely means steam), your fingers will get burnt... (steam holds about 2 1/2 times as much energy gram for gram as aluminum, water holds about 5 times as much. plus there's the energy it took to boil the water.)

You have some flaws in this logic that I will point out individually with explanation.

The specific heat is the amount of heat needed to raise 1 gram of a substance by 1 degree celsius. The specific heat of steel is lower, meaning it needs less energy to heat it for each degree (for the same amount of mass) as aluminum.

Yes.

Thus foil made out of steel would contain less energy than aluminum foil (of the same size and thickness) and would burn your hand even less.

No, foil made out of steel would contain less energy than aluminum foil (OF THE SAME MASS). Because of differing density, steel foil and aluminum foil of the same size and thickness would have different mass and, consequently, different amounts of energy at the same temperature. (I discuss this density effect in the third set of numbers presented)

Nonetheless, the specific heat of the substance, along with the mass and temperature of the substance determines how much heat is present to burn your fingers.

Yes, exactly what I said in the third part of my post:

Here you see that stainless steel is approaching 3x the density of aluminum. So for the same sized (volume) piece of material, as you proposed, the resulting energy of each piece of the same volume is (in units of Btu/in^2-F)

Stainless 316_____0.03408
Stainless 440_____0.03069
Aluminum 1100____0.021168
Aluminum 6061____0.020972
Aluminum 7075____0.02323

Now you see that stainless steel pieces of the same geometric size will contain about 150% of the thermal energy of aluminum pieces at the same temperature.

Unless my calculations are wrong, I don't see how you can conclude anything else from this data. This is the energy stored per unit volume per degree, which is exactly corresponding to the 'size' and 'thickness' you speak of.

Thus, your assertion that specific heat is 100% wrong is also wrong.

I don't see how, since I clearly showed that while having a higher specific heat, aluminum foil contains less energy than steel of the same dimension due to DENSITY. If it were determined by specific heat, the aluminum would have more energy, thus be more likely to burn, which is not the case.

The actual answer is: Low mass and relatively low specific heat are the reasons your fingers don't get burnt. If you could touch the same mass of water with your fingers, at the same temperature (which likely means steam), your fingers will get burnt... (steam holds about 2 1/2 times as much energy gram for gram as aluminum, water holds about 5 times as much. plus there's the energy it took to boil the water.)

Agreed, this is basically a restatement of 'it is thin and doesn't store much energy' that seems to be the consensus of why foil doesn't burn you.

You're right. I stand corrected (particularly on the same size and thickness of foil... a blunder on my part.)

Here you see that stainless steel is approaching 3x the density of aluminum. So for the same sized (volume) piece of material, as you proposed, the resulting energy of each piece of the same volume is (in units of Btu/in^2-F)

Stainless 316_____0.03408
Stainless 440_____0.03069
Aluminum 1100____0.021168
Aluminum 6061____0.020972
Aluminum 7075____0.02323

Now you see that stainless steel pieces of the same geometric size will contain about 150% of the thermal energy of aluminum pieces at the same temperature.

But, shouldn't the units be Btu/in^3-F?
And, the energy stored per unit of volume, unless I'm mistaken again, would be calculated by the specific heat times the density.

 

[ZeroNine8]

*mutters something about units*
yeah it should be in^3