How come no CPU coolers w/heatpipes and vapor chamber?

[80251]

Not if the fluid inside cannot vaporize and condense properly.

But that's counter-intuitive and doesn't match the facts that I've seen.

Um, then why does my NH-D15s cool more efficiently at an ambient temp of 60°F than 80°F?

Please show me an instance where a significantly lower ambient temperature results in a heatpipe cooler's resultant delta-T being HIGHER at the LOWER ambient temperature.

Furthermore, for heatpipe coolers that ultimately rely on air as the cooling medium, the convective heat xfer equation is DIRECTLY proportional to the difference in
temperatures between the cooling medium and the surface to be cooled, ergo, even though your heatpipes are less efficient at lower temperatures the convective
heat xfer of the heatpipes and fins may more than overcome the lowered efficiency of the heatpipes themselves:

ibid:
https://www.engineeringtoolbox.com/convective-heat-transfer-d_430.html

 

[Count von Schwalbe]

But that's counter-intuitive and doesn't match the facts that I've seen.

Um, then why does my NH-D15s cool more efficiently at an ambient temp of 60°F than 80°F?

Please show me an instance where a significantly lower ambient temperature results in a heatpipe cooler's resultant delta-T being HIGHER at the LOWER ambient temperature.

Furthermore, for heatpipe coolers that ultimately rely on air as the cooling medium, the convective heat xfer equation is DIRECTLY proportional to the difference in
temperatures between the cooling medium and the surface to be cooled, ergo, even though your heatpipes are less efficient at lower temperatures the convective
heat xfer of the heatpipes and fins may more than overcome the lowered efficiency of the heatpipes themselves:

ibid:
https://www.engineeringtoolbox.com/convective-heat-transfer-d_430.html

Please don't take what I said out of context. We were talking about heat pipes losing performance at winter temperatures (we are not talking about 60 vs 80 here).

Quite for reference:

IIRC, (ambient-terrestrial) Heat Pipes/Vapour Chambers drastically lose performance in "Winter Temperatures" and can 'heat soak'.
Basically, if you use a heatpipe outside of its expected operating temperature range, it works much worse than solid metal.

Basically, if the phase changing fluid inside cannot vaporize, it cannot flow to the other end of the heatpipe to deposit its stored heat at that end. You essentially are then relying on the conductive properties of the wall of the tube to transfer the heat, which is much less efficient.

In practice, a CPU cooler is unlikely to suffer this issue for two reasons - the input temperature is quite high, and will boil the fluid regardless of ambient temperature. This just means that the majority of the cooler is wasted space, as the fluid is condensing early in its travel to the other end of the tube. The other reason is that the temperature range at which this problem might occur would most likely cause issues due to condensation long before this is experienced.

 

[Mussels]

Um, then why does my NH-D15s cool more efficiently at an ambient temp of 60°F than 80°F?

It can cool less efficiently, but still cool the CPU better because it has an easier job at lower ambients.

You're thinking of the final temperature only, not the individual components and each temperature along the way

Basically, if the phase changing fluid inside cannot vaporize, it cannot flow to the other end of the heatpipe to deposit its stored heat at that end. You essentially are then relying on the conductive properties of the wall of the tube to transfer the heat, which is much less efficient.

^ this, good description