Conduction, Convection and Radiation...

... and the most important of these is Conduction...

So I’m watching Mission to Mars right now, and like Sunshine, it gets the whole idea of being exposed to outer space somewhat… wrong.

Heat’s a finicky thing. What you experience as “heat” is actually a relative measurement for the most part – it’s how hot you are compared to other things.

Heat also only flows from hot things to cold things. To do that, it needs a way to spread the love, and that is where the holy trinity of Conduction, Convection and Radiation come in.

(Why does heat only flow in one direction? Well… think of it this way. Heat doesn’t really flow, per se. It just averages out. So if something cold touches something hot, the heat between the two will slowly average out, making the cold thing warmer, and the hot thing colder. If you think of the hot thing having more energy, logically, the heat will flow into the cold part. But really, it’s just mixing everything up. Now, if you want to do engineering with it, using the concept of heat moving to cold makes everything much easier).

Now, Conduction works best. Molecules vibrate against one another, and those vibrations move really well when those molecules are close together. So for the biggest bang for your buck, you want solid connection.

Convection doesn’t work anywhere near as well – because the molecules are really far apart. Think of Conduction as a Newton’s Cradle, or making the break on a pool table. Convection is the pool game while it’s in play – you can shoot the cue ball anywhere you want, and you might hit one or two, but you’re not going to hit all of the balls. It just doesn’t work anywhere near as well.

Radiation is the last one… and it’s the weakest. Photons don’t carry anywhere near as much energy as smacking little molecules against each other. (The Sun is an exception here, because the Sun outputs an astronomical number of them all the time).

Being in Deep Space

So, here’s the deal right… Space is a vacuum. It’s not cold. In fact, one of the biggest difficulties that satellites have is getting rid of heat, not keeping them warm! (The reason why pictures of satellites usually show them covered in gold foil is because gold is one of the best reflectors of infra-red radiation we have – it’s shielding them from the heat). You won’t lose much body heat to space. You certainly won’t freeze.

According to Nasa, you might get the bends (if you survive without oxygen for 30 minutes… which is unlikely). You won’t explode. You may get a full body hickey. And you may rupture your lungs if you try to hold your breath. Your saliva might boil away, but let’s face it – skin is pretty hardy stuff.

But freeze? No way. No conduction. No convection. All you’ve got is radiation – and believe me, that won’t make that much of a difference to you.

Keeping your House Cool

This also has some applications to keeping your house cool. You can’t do anything about Conduction, so forget about it. During the day, keep your windows and doors closed to prevent convective heat transfer. And cover your windows in aluminum foil to prevent radiative heat transfer.

Then, during the night, set up a fan at the top of your house, blowing air out. And another on the ground floor, pumping air in. Hey presto – it’s the best way to keep your place cool other than buying an AC unit.

About the author

Simon Cooke is an occasional video game developer, ex-freelance journalist, screenwriter, film-maker, musician, and software engineer in Seattle, WA.

The views posted on this blog are his and his alone, and have no relation to anything he's working on, his employer, or anything else and are not an official statement of any kind by them (and barely even one by him most of the time).

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