ibook g3 heat pipe and heat spreader question

Thanks for the response. There IS liquid in the heat pipe that is attached to the heat spreader on one end, and the heat sink on the other; though it isn't what is normally thought of as "liquid" cooling). It's a copper tube, and usually filled with some sort of working fluid: water, ammonia etc under a vacuum and it uses the latent heat of vaporization to remove heat and transport it to the heat sink where the fan dissipates it. They are actually quite common in laptops because of their efficiency and zero maintenance and have been around for some time. I could speak generally about it for my research, but I'd like to know specifics. If your buddy knows anything specific at all about the heat pipe, I would truely be grateful!

Excellent thanks for that! So are you saying that within this particular model or range of models there could be any one of 2+ different coolant types?

Thanks for trying at least 🙂

On reading up a little bit, I don't believe that the working fluid is metallic sodium since that should be used in higher temperature applications. It is one of these: water, ammonia, acetone or methanol. If you hear anything else in the meantime, I'm all ears!

Thanks Richard.

After researching a little bit today, i believe that the working fluid is actually water. The thing with heat pipes is that they are under vacuum. This means that water could actually boil at anything above zero degrees (or room temperature), depending on what partial vacuum was chosen for the application. the choice of fluid has a lot more to do with operating temperature range than anything else, hence why sodium or mercury are very unlikely candidates in this case. Although water isn't really a "phase change material" in this particular case, you do have the right idea since there IS two phase heat transfer going on here (which is why this isn't "liquid" cooling if that makes sense). Silicone hasn't been used in any heat pipe application that I am aware of.

I'm actually more interested in the wicking structure inside. Unfortunately the computer is not owned by me, and I'm sure he would be annoyed if I took a hacksaw to his G3 cooling solution 🙂

I can at least ask 😉

if i find out anything, i'll post

Alex

It's just amazing to me that they acquiesced to such extreme cooling methods for those CPUs....

Yeah I'd definitely be interested. If you have one of those small bubble wrap dvd mailers laying around I'll paypal you like 3 bucks if you don't need the part anymore. It would definitely be used in the name of science 😀

If not, no worries, I'll figure something out!

I cut open the heat pipe today, and the results aren't surprising. The wicking structure is micro-grooved and I'm 90% sure the working fluid is simply water as I thought. the water is just below saturation temperature where it starts at the processor/gpu/bridge. any added heat when the cpu is active causes boiling which creates a pressure gradient. the vapor is then forced down the tube to the heat sink where the fan blowing on the fins condenses it back into liquid form. these micro-grooved structures are essentially wicks and allow the water to make its way back toward the processor via capillary action in order to be vaporized to start the process again. this micro-grooved wick with water is pretty much the simplest (cheapest) form of heat pipe you can have so it's understandable why apple used it. we're not exactly dealing with super-high heat levels 🙂

wikipedia:

"A heat pipe is a hollow tube containing a heat transfer liquid. As the liquid evaporates, it carries heat to the cool end, where it condenses and then returns to the hot end (under capillary action, or, in earlier implementations, under gravitation). Heat pipes thus have a much higher effective thermal conductivity than solid materials. For use in computers, the heat sink on the CPU is attached to a larger radiator heat sink. Both heat sinks are hollow as is the attachment between them, creating one large heat pipe that transfers heat from the CPU to the radiator, which is then cooled using some conventional method. This method is expensive and usually used when space is tight (as in small form-factor PCs and laptops), or absolute quiet is needed (such as in computers used in audio production studios during live recording). Because of the efficiency of this method of cooling, many desktop CPUs and GPUs, as well as high end chipsets, use heat pipes in addition to active fan-based cooling to remain within safe operating temperatures."

Richard, I don't know if this helps you with your G5 cooling issues since i do beleive the G5 uses actual liquid cooling in the traditional sense (heat exchanger with EG/water). liquid flows at a positive pressure to cool using sensible heat without boiling where a heat pipe like this is under a vacuum (negative pressure) in order to facilitate the boiling process to cool via latent heat. really they are 2 very different processes... I don't know why they didn't use a dielectric coolant to prevent these G5 leak reliability issues they had. there's less heat removal capacity, but at least if you get a leak the whole system isn't destroyed.

I hope this information helps you out in some way though!