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Say that I have a hot sandwich and a cool salad, both in functionally-identical plastic containers that provide no effective heat insulation. I need to stack these two containers for ease of carrying, and I want to warm up my salad as little as possible. (The salad won't affect the sandwich much, as it's much closer to ambient temperature.) Which container do I put on top?

If I put the sandwich container on top, I have the heat source in almost direct contact (via two thin layers of plastic) with the air above my salad in that container.
If I put the salad on top, the salad is being heated by the air in the sandwich container. The air is cooler than the sandwich itself, but it's being applied directly to the salad.
I also know that hot air rises, but I don't know if that's relevant within this small system.

So, which way should I stack my food to minimize the heat transference?

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  • $\begingroup$ You can always make two salads and two sandwiches and compare. $\endgroup$
    – jinawee
    Jul 20, 2015 at 20:20

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You should run the experiment. If you've got 4 plastic bins, one weekend, just half-fill all of them in two pairs, each pair consisting of one half containing water from a pot on the stove, the other containing water from the fridge. Measure the temperature of the "cool" water after an hour or two.

With that said, air mostly distributes stuff by convection: in other words mostly things move around by flowing with the air as it moves around, rather than by moving around within a stationary airstream. This means that there's a solid expectation that the situation which places a convective boundary between the two (i.e. hot container on top) is going to transfer less heat than the reverse.

Of course, if you want to solve the problem, you can insulate the two from each other with a piece or two of cardboard...

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