Whats the purpose of the heatsink?

[Josh9.0]

My 1st post!
It may have been answered here multiple times. Sorry if that's the case. I haven't found it. Here goes:

What's the purpose of the finned aluminium heatsink used in the J-head style of 3D printer ?
I know you need to get the filament very hot to melt it, but why cool it down just before heating it?
I can imagine a few vague reasons why, but nothing definite enough to be sure.

I asked a (Chinese) seller of the part, on ebay. I asked in plain English, but they don't understand me.
I asked an Australian seller (I'm in Australia) of the part on ebay. He wasn't sure either.

Thanks
-Joshua (nickname: Dodgy)

[CaptainObvious]

The purpose is to make a sharp temperature gradient in the filament path, that is to say, you want your filament to be cool enough so it doesn't deform until the moment it enters the nozzle where it melts; if heat travels up the feeding tube the filament could soften, buckle as it's being pushed and jam the extruder.

[Davo]

Like the Captain said: you want it cool where you're feeding it, and hot where you're melting it.

[Josh9.0]

Ah... thanks. I see now!
-Joshua (Dodgy)

[Josh9.0]

So, if I want to make my own heatsinks, and make them very slim, then what's wrong with making them non-finned, but a spiral tubular channel, for coolant/water to pass though? Like a car radiator, but without the fins. More like the water jacket (condensor) of a distillation still. I would use a thin copper/aluminum tube wrapped around the aluminium feeding tube (isn't that like a nasogastric tube?), and then the coolant can pump through, to keep it cool. With the addition of potential Peltier devices to cool the fluid elsewhere.
Or even, just mount 3 or 4 slim Peltiers to the feeding tube, and use a square feeding tube for 4 Peltiers.

Thanks.
-Joshua (Dodgy)

[Davo]

In theory, water cooling works fine.

In practice, it is a much more complex system (more things that can go wrong) than mere cooling fins (surface area to radiate heat).

Locally mounted Peltiers are a fine idea. Give it a go and let us know!

[CaptainObvious]

In theory, water cooling works fine.

In practice, it is a much more complex system (more things that can go wrong) than mere cooling fins (surface area to radiate heat).

Locally mounted Peltiers are a fine idea. Give it a go and let us know!

I've been toying with the idea of building a new printer with a heated chamber, and using water cooling for the print head since just circulating the hot air inside the chamber wouldn't do much good.
So far I've thought of running the coolant tube inside a larger tube that would also carry the Bowden filament tube inside, that way the filament is also kept cool as it moves down the tube. I promise not to say "tube" for the rest of the day now. :P

[Josh9.0]

Very nice idea! Mind if I make a prototype first??!
You'll have to connect to that water pipe too! And let the Bowden tube go through/around that!
Plus, you can't just pump water down to the area just above the head, you have to bring it back to the pump (it will be warm, probably).

I will have a Peltier heat exchanger (snaked pipe, over or between 2 Peltiers) near the pump, to ensure it goes back to the print head cold.

What's wrong with the word tube? Reminds you of vacuum tube (thermionic valve) ? Or London's underground train system ?

-Joshua (Dodgy)