Sip Posted May 12, 2004 Report Share Posted May 12, 2004 Why is aluminum foil that has been in a 425F oven for 30 minutes cool to the touch? Quote Link to comment Share on other sites More sharing options...
Maral Posted May 12, 2004 Report Share Posted May 12, 2004 MAGIC Quote Link to comment Share on other sites More sharing options...
DominO123 Posted May 12, 2004 Report Share Posted May 12, 2004 Why is aluminum foil that has been in a 425F oven for 30 minutes cool to the touch? Is that a real question that you are asking Sip? Quote Link to comment Share on other sites More sharing options...
Sasun Posted May 12, 2004 Report Share Posted May 12, 2004 Why is aluminum foil that has been in a 425F oven for 30 minutes cool to the touch? I think it has to do with 2 reasons. 1) Reflecting heat in the oven. In the oven the heat is transmitted to the foil (and food) mostly through infrared waves and air. Air has little heat conductivity, and infrared waves are bounced back by the foil surface which is a near mirror. 2) The foil has weak heat conductivity itself (maybe by desing), so even from the points of contact with food not much heat is transmitted to the other parts of the foil. Quote Link to comment Share on other sites More sharing options...
bellthecat Posted May 12, 2004 Report Share Posted May 12, 2004 Because aluminium is a very bad conductor of heat. And your roast chicken is not. Quote Link to comment Share on other sites More sharing options...
Twilight Bark Posted May 12, 2004 Report Share Posted May 12, 2004 Because aluminium is a very bad conductor of heat. And your roast chicken is not. Oh come on. It is because it is a good conductor of heat, and more importantly it has a low heat capacity. What little "heat" it has quickly escapes the foil as soon as you take it out of the oven. Quote Link to comment Share on other sites More sharing options...
Sip Posted May 12, 2004 Author Report Share Posted May 12, 2004 Is that a real question that you are asking Sip? Yes it is. Everytime I take pizza out of the oven I can just grab the foil and take it out of the oven while everything else is 425F degrees in there. Disclaimer: Do NOT try this at home. Quote Link to comment Share on other sites More sharing options...
Sip Posted May 12, 2004 Author Report Share Posted May 12, 2004 Oh come on. It is because it is a good conductor of heat, and more importantly it has a low heat capacity. What little "heat" it has quickly escapes the foil as soon as you take it out of the oven. So in other words, the foil is at 425 degrees just like everything else but it gives the heat off very rapidly once the oven door is opened? That would kinda make sense. It is still pretty strange though. Quote Link to comment Share on other sites More sharing options...
Sasun Posted May 12, 2004 Report Share Posted May 12, 2004 (edited) Oh come on. It is because it is a good conductor of heat, and more importantly it has a low heat capacity. What little "heat" it has quickly escapes the foil as soon as you take it out of the oven. Iron is a better conductor of heat. Try to touch an iron sheet in the oven But you are right that it has little "heat capacity" which is proportional to the mass of the foil. The conductivity of the foil does not play important role in loosing heat, rather the conductivity of the things (air, hands, etc) to which it will loose heat. I am quite sure the foil is cool even when the oven is closed. I am suspecting that the surface of the foil is covered with some non-metallic layer which has lower conductivity than aluminum. I think you can see it if you gently scratch it off. Edit: Well, there is one way to test, put the whole roll of foil in the oven. (Remember to remove any non-aluminum parts such as the paper or plastic carcass). The roll is much heavier than a sheet, so it has much more capacity of heat, it won't loose heat quickly if it is indeed hot. Edited May 12, 2004 by Sasun Quote Link to comment Share on other sites More sharing options...
DominO123 Posted May 12, 2004 Report Share Posted May 12, 2004 Er... I forgot to answer you Sip. The reason I asked the question is that I thought you knew the answer. The reason is that alluminium has a very good heat dissipation and conductibility. BTW Sasun, I am pretty sure that alluminium heat condictibility is better than Iron. Quote Link to comment Share on other sites More sharing options...
ED Posted May 12, 2004 Report Share Posted May 12, 2004 Because aluminium is a very bad conductor of heat. And your roast chicken is not. Wrong Steve, Aluminum has one of the best conductivities of all metals. That’s one of the reasons it cools so fast. I know because I deal with aluminum almost every day. Quote Link to comment Share on other sites More sharing options...
DominO123 Posted May 12, 2004 Report Share Posted May 12, 2004 (edited) low heat capacity. Oh yeh! I forgot this one. Alluminium density/conductivity is pretty low, which means that by having a low density, it does not have the "reserve" to keep all the heat so it dissipate it. Edited May 12, 2004 by Fadix Quote Link to comment Share on other sites More sharing options...
bellthecat Posted May 12, 2004 Report Share Posted May 12, 2004 Oh come on. It is because it is a good conductor of heat, and more importantly it has a low heat capacity. What little "heat" it has quickly escapes the foil as soon as you take it out of the oven. Yes, sorry, that's actually what I meant to say , and that the roast whatsit has a very high capacity for heat (i.e. energy) storage. Quote Link to comment Share on other sites More sharing options...
bellthecat Posted May 12, 2004 Report Share Posted May 12, 2004 But foil is also cool because you can make pretty things out of it! Quote Link to comment Share on other sites More sharing options...
Sasun Posted May 12, 2004 Report Share Posted May 12, 2004 BTW Sasun, I am pretty sure that alluminium heat condictibility is better than Iron. I actually checked, you and Edo are right. Aluminum has several times higher conductivity. On the other hand, can you say that aluminum will lose heat in vacuum because of high termal conductivity? Quote Link to comment Share on other sites More sharing options...
Sasun Posted May 12, 2004 Report Share Posted May 12, 2004 But foil is also cool because you can make pretty things out of it! Really? What cool things can you make with foil Steve? I thought it is only used in the kitchen? Quote Link to comment Share on other sites More sharing options...
DominO123 Posted May 12, 2004 Report Share Posted May 12, 2004 (edited) On the other hand, can you say that aluminum will lose heat in vacuum because of high termal conductivity? Its high termal conductivity has a role, but dissipation as well, its high heat dissipation is due to its low density. Density act as a reservoir for heat, when a metal has low density it can not keep the heat... and when on top of that it is a very good thermal conductor, it helps alot for the evacuation of the heat. Edited May 12, 2004 by Fadix Quote Link to comment Share on other sites More sharing options...
Azat Posted May 12, 2004 Report Share Posted May 12, 2004 Why is aluminum foil that has been in a 425F oven for 30 minutes cool to the touch? And now we know why your brother is winning prizes in Science and Engineering and you are not. Quote Link to comment Share on other sites More sharing options...
Sip Posted May 12, 2004 Author Report Share Posted May 12, 2004 Hey! There are no dumb questions. Just dumb people. Thanks for the replies fellas. The heat capacity explanation cleared things for me as the only thing that was puzzling me was how it would stay cooler than the ambient while it didn't stay cool at all ... it just gave off the little heat it had very rapidly. Quote Link to comment Share on other sites More sharing options...
bellthecat Posted May 13, 2004 Report Share Posted May 13, 2004 Really? What cool things can you make with foil Steve? I thought it is only used in the kitchen? What? I thought everyone from age 1 to 100 instinctively makes things like rings or aeroplanes or bells or stick-animals from their aluminium "tin-foil" chocolate wrappings. And how many corny films have the hero useing foil to complete an electrical circuit to diffuse the bomb and save the day. But I never did get the significance of the tin-foil animals in "Blade-Runner". Enlighten me anyone? Quote Link to comment Share on other sites More sharing options...
Sip Posted May 13, 2004 Author Report Share Posted May 13, 2004 I have actually used foil from a gum wrapper to bypass a burnt fuse on my blazer while offroad once. Quote Link to comment Share on other sites More sharing options...
Sasun Posted May 13, 2004 Report Share Posted May 13, 2004 What? I thought everyone from age 1 to 100 instinctively makes things like rings or aeroplanes or bells or stick-animals from their aluminium "tin-foil" chocolate wrappings. And how many corny films have the hero useing foil to complete an electrical circuit to diffuse the bomb and save the day. But I never did get the significance of the tin-foil animals in "Blade-Runner". Enlighten me anyone? This field of life has escaped me (except Sip reminded me I used to make fuses unsuccessfully from a chewing gum foil). Quote Link to comment Share on other sites More sharing options...
vava Posted May 13, 2004 Report Share Posted May 13, 2004 And now we know why your brother is winning prizes in Science and Engineering and you are not. Quote Link to comment Share on other sites More sharing options...
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