Why do all heatpipe coolers use rigid pipes

[picomode]

Why are all heatpipe coolers connected with rigid pipes between the base and the sink? Using flexible hoses, say silicon hose, we'd be able to mount that extra large cooler on the 120mm fan cutout and not worry about the size or weight of the cooler. A hose would not be a good thermal conductor, but isn't it the gas in the pipe that transfers the heat?

Isn't the concept of a heatpipe, like a mini refrigerator, except that it uses convection instead of a motor ? I am assuming there is a refrigerant equivalent to freon inside the pipe ?

 

[equivocality]

Isn't it nitrogen or something in there?

 

[Groveling_Wyrm]

The cooliant used in heatpipes is usually something ranging from distilled water to R-134A freon...but NOT nitrogen.

Heatpipe coolers work on evaporation. At ambient temps, the coolant in the heatpipe should be able to be in a liquid state, and when heated, it will evaporate and work its way away from the CPU.

Once it hits the area where the fins are, the fins will take the heat back out of the coolant, changing it back to a liquid where it condenses on the side of the heatpipe, where there is a special coating to help it condense. It will then follow gravity and pool again at the cpu to gain heat and evaporate again.

If you used flexible hoses, then the most likely result would be pressure issues with the hose and condensation issues. The end result could easily result in the coolant condensing in the tube before it reaches the cooling fins, due to kinking or bending the hoses the wrong way. This would make the cooler less efficient.

 

[morerevs]

It's also very hard to solder cooling ribs to a flexible hose This means they would have to make the actual heatsink more like a waterblock and that would raise cost me thinks. I could be envisioning this the wrong way but in my mind this would be close to a watercooled setup with brackets to hold the actual heatsink/fan contraption in place???

Anyways

nvm I just saw the "fan cutout" part so ditch the brackets. But it would still be like a watercooled setup only with freon?? cool

 

[IcY18]

Because Copper heatpipes transport the heat better most other metals. Also it would have to be some pretty good flexible pipes to withstand temperatures of 75C or greater.

 

[equivocality]

I know in satellites, the engineers use a substance that does not evaporate. This is why I said nitrogen, as I had a talk with someone recently, however I couldn't remember if he said nitrogen or another substance.

I will add something extra that is on my mind; The materials these engineers use to conduct heat are very impressive. An example of this would be, I'll call it a 'super-conducting-rod' to name it for now. When holding this piece of material in one hand, and touching the other end with a cigarette, you WILL be burned as if you were holding the cigarette itself to your own skin.

I'm amazed at some of the things that are devised.

 

[picomode]

It appears there is a wick of some sort, to facilitate the movement of the condensed liquid in the pipe. Here's a short but interesting FAQ from a manufacturer of heat pipes:

http://www.aavidthermalloy.com/products/heatpipe/index.shtml

If they can get over the problems with the bending of the pipes I see no reason why they could not use flexible hoses. This could be the next big thing in coolers. Almost makes me want to buy a waterblock and a bottle of alcohol or a can of butane and set up an experiment. I would use silicon hose with a spring inside for the wick and also to prevent the hose the hose from kinking.

Nitrogen might be good instead of air since it will prevent oxidization of the internal components, minimizing contamination.

 

[Groveling_Wyrm]

Nitrogen is NOT a good idea for use in heatpipes. People who have phase-change cooling systems in their computer, and cool their computers in the range of -100 to -150F do not use Nitrogen.

Why is this? The problem with Nitrogen is that it boils at -320F, which is far BELOW ambient room temperatures. This will not work effectively for heat pipe coolers, or for cooling in multi-phase cooling systems.

A properly working heat-pipe cooler MUST have a liquid that evaporates with the heat produced, to get the performance needed. In essence, a heat pipe cooler must be able to have a liquid at room temps, that evaporates when the heat is applied. It is the process of evaporation and condensation that effectively moves the heat in these types of coolers.

To attain the best performance in a heatpipe, your liquid must be almost ready to evaporate at room temperatures. Then with the least amount of heat applied, the liquid evaporates, starting the evaporation/condensation process quickly after the heat is applied.

As far as wicking materials, the wicking material is usually hard and cannot be bent. Therefore, putting the wicking materials inside a flexible hose will most likely result in the material cracking, falling apart, and piling up at the bottom of the heatsink, or worse, blocking the hose, causing complete failure.