Heat Pipe "Wick"

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pcy
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Heat Pipe "Wick"

Post by pcy » Fri Aug 14, 2009 4:03 am

Hi,

I understand broadly how a Heat Pipe works, but If anybody knows in more detail:

Two Questions:

1. What is thi structure of the "Wick" on the internal wall of the pipe. I assume it's just a collection of grooves crated when the pipe is extruded to help return the the fuid in its liquid state to the hot end by improving capillary action.

2. How easily can the "Wick" be damaged by bending the pipe?


Thanks


Peter

Metaluna
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Post by Metaluna » Fri Aug 14, 2009 6:04 am

According to Wikipedia:

http://en.wikipedia.org/wiki/Heat_pipe

the wick "is typically a sintered metal powder or a series of grooves parallel to the pipe axis, but it may be any material capable of exerting capillary pressure on the condensed liquid to wick it back to the heated end."

I would think a sintered wick would be somewhat brittle so you wouldn't want to bend it too much. But either way, I suspect that any bends, especially sharp ones, reduce the efficiency of the capillary action.

pcy
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Post by pcy » Fri Aug 14, 2009 6:59 am

Hi,

Ok... put it another way, are the bends put in by teh Cooler manufactures made in any special way to prevent damage, or can we reasonably assume that any bends of teh same sort of radius can easily be made.

Why would sintered metal, or just plain grooves be more brittle than ordinary metal? How would you add a sintered metal wick to an extruded copper tube?



Peter

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Post by rocket733 » Sun Aug 16, 2009 6:17 pm

I'm pretty sure the same bends can be made to most heatpipes, I haven't run into anything that would go contrary to that statement. Just be careful not to damage the heatpipe, I'd consider looking into a tube bender (either the spring typer or the plumber professional kind). Also I'm pretty sure the sintered wick is part of the manufacturing process of the cooper tubing and would be difficult to add to your own extruded copper tube. Are you looking to make your own heatpipes?

pcy
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Post by pcy » Mon Aug 17, 2009 3:11 am

Hi,

Thanks. That's what i was thjinking.

If the pipes are extruded then all heatsinks must have the bends put in afterwards.

No - I was thinking of manufacturing my own CPU coolers, and the only difficult bit appears to be the heatpipes. I'd probaly buy them in from some plant in China because I suspect there is quite a lot of detailed research needed into the exact form of the Wick, and the internal fluid.

The motivaton is that I want to be able to make the coolers to the optimal size and shape for my existing and planned PaQ cases.

Also - if you go down the Direct Contact route like the Xigmatek coolers (which I currently use, but with 140mm fans) the best section shape for the pipe is no longer a circle - it's hard to calulate but I suspect it's more like a reactangle with 2:1 aspect ratio and slightly radiused corners to reduce stress concentration caused by bending.


Peter

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