Expert: Paul Soderman - 7/10/2006

Question
Thank you kindly for taking the time to answer my silly question.  It is just that i have to have it written up and in school tomorrow and i was not sure whether i was on the right track.  I did an experiement earlier on this evening using a air tight container, bubble wrap, newspaper, tinfoil and left one exposed on a plate.  The ice cube in the bubble Wrap lasted the longest- one and a half hours!  The one in the tin foil (aluminium foil) melted first and i do not know why.  I thought it would have lasted longer. The plate was next, then the air tight container and the newspaper was the second to last to melt.  I also do not know why the ice cube in the bubble wrap lasted the longest.  But I will have to figure it out for tomorrow morning because i know you are probably very bored and tired now of answering some strangers questions here in Liverpool UK.

Once again, thank you.
This is a great website!
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Followup To

Question -
I thank you for responding to my question but would you be so kind as to expand a little more on your answer.  I know that wrapping it up will slow down the melting process but that depends on what you wrap it up with or put it in to prevent a heat souce from reaching it.  The ice cube left unwrapped will melt quicker because the heat source will be able to seek out the cold much quicker than the ice cube wrapped ;but i wanted you with you knowledge to make a longer statement.  Go on, humour me.
cheers.
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Followup To

Question -
Three children were discussing how to prevent an ice cube melting.  These were their ideas:

1  Wrap it up.  That will stop it melting

2  Don't wrap it up. That would make it melt    more quickly.

3  Wrapping it up won't make any difference to how quickly it melts.

Decide which statement you agree with and give your reasons for agreeing with it.

Cheers

Answer -
Well Sadie - this is a trick question.  Number two is the only statement that is true, but it doesn't address the original problem.  Number one is almost true, and does address the original problem.  I'll let you figure out why.

Paul

Answer -
Oh Sadie - you said it pretty well.  Wrapping or enclosing an ice cube will provide insulation that slows the heat transfer from the warm exterior to the cold interior or vice versa if it is colder outside.  The heat transfer rate via convection depends on the temperature difference, the thickness of the insulation, and the thermal resistance of the insulation.

There is not much more to say without getting into molecular motion or secondary effects such as wind, thermal radiation, color, etc.

Paul

Answer
Wow - Liverpool, home of the Beatles (I think) - my favorite group when I was in college.

OK - that was a good experiment, and I am not entirely sure of the explanation, but here is what I think:

1.  The bubble wrap worked well because it is thick, has two layers of plastic, and a trapped air space between - kind of like a wall.

2. The newspaper is next because paper is a good insulator, but thin.

3.  The airtight container should have been better, but am not sure of the material or geometry.  Maybe the heat came in easily from the bottom.

4.  The aluminum is a little surprising, but I know that aluminum is a very good conductor of heat.  When I reach in the oven, I can touch aluminum foil with my bare hands because it doesn't hold heat.  Why it is better than no covering is a little unclear, but it may be because close contact with the ice and large surface area actually helps with the heat transfer; i.e., the aluminum acts like a radiator that absorbs heat easily from the exterior and convects it easily to the ice......strange, but true ?

Wish I could be more clear Sadie - but I am an aero engineer after all.  Good luck.

Paul