Cooling [SFF Network] Passive Cooling - An Experiment

[confusis]

One of the major issues we come across when building our Small Form Factor systems is cooling. There just never seems to be enough space to cool our systems efficiently and quietly without investing major effort, or considerable expense.

Read more here.

 

[Kooki]

Very interesting concept to investigate.
I wonder what would be the "size" of the heat-sink needed to cool a low TPD CPU when doing light tasks like browsing or document typing, instead of the CPU burning prime95.

 

[confusis]

A lot smaller! Between tests, the heatsink was barely warm to the touch. You'd want to have some cooling headroom though - in case something decides to lock up and throw the CPU a 100% load!

 

[Kooki]

A lot smaller! Between tests, the heatsink was barely warm to the touch. You'd want to have some cooling headroom though - in case something decides to lock up and throw the CPU a 100% load!

Yeah... headrooms are important...
So does that mean we could, possibly make a reliable semi-passive "small" heatsink? I don't have many parts to test nor experience with hardware... Do you have any idea of the size of the heatsink to make a semi-passive build?

 

[confusis]

Depends on the processor. The test processor was 65w, so on say, a 35w Pentium, you may get away with something the size of the NH-L12 or Scythe Big Shuriken. It would need to be tested though!

 

[Kooki]

I'd imagine for convection and "natural heat transsfer" to occur optimally one would need a large surface area for the job. Though Scythe Big Shuriken works great with the fan i doubt it would be a good candidate for passive / semi-passive cooler... But the NH-L12 might work very well...
Unfortunately I can't find any sort of testing about trying to use these consumer coolers as passive coolers...

 

[confusis]

The scythe Big Shuriken does have some decent surface area, but it's advantage may be the low restriction under the heatsink enabling horizontal layout of the board, much like the L12.

 

[Kooki]

The scythe Big Shuriken does have some decent surface area, but it's advantage may be the low restriction under the heatsink enabling horizontal layout of the board, much like the L12.

And it's also under 60mm height total... I hope someone in these forums could test this. :x

 

[confusis]

If i hadn't killed the Thermal test board ( -_- ) i would be happy to test the other coolers i've reviewed before for passive mode cooling.

 

[Kooki]

If i hadn't killed the Thermal test board ( -_- )

You killed it in this last test!? ;_;

 

[confusis]

Yeah. I think a VRM somewhere went short. Board won't power on, even for a millisecond! woops :/ Not sure if the test killed it, or my bad luck with MSI products has returned.

 

[Kooki]

What a bummer!

 

[confusis]

Will replace it in a few weeks. I have some more cooler reviews coming this week, but as they are bigger coolers, I will use my 'extreme' test rig

 

[Kooki]

We are all waiting for more great reviews

 

[iFreilicht]

It seems the heatsink you've used here might blur the test results a bit. It's top face is nearly quadratical, so the difference between airflow from the front or the side is going to be low, and the hole in the middle could allow for some kind of continuous airflow to form.

I did a similar test with some Arctic Cooling tower cooler and a 45W CPU, and that got up to 81°C under 100% load in horizontal orientation and started throttling. In vertical, it was at 72°C. Didn't test sidewards vs. frontwards airflow, though.

 

[Phuncz]

Awesome article !

As such, optimal heatsinks for passive cooling are large, preferably dark in color

What's the reasoning behind this ? Because metals can be plated or even painted, so I'm not sure what the reason is.

I'm curious about the topic of passive cooling, some questions that I can think of:
- how much heatsink surface area would you need per 10W of heat ? (considering adequate heatpipes)
- would it be conceivable to cool a 200W GPU passively ?
- how much "airflow" does passive cooling generate at ~60°C with 20°C ambient ?
- what are the best performance per watt components for a completely passive gaming PC ?

 

[iFreilicht]

would it be conceivable to cool a 200W GPU passively ?

130W seem to be possible, at least with the CR-95C.

 

[Phuncz]

That NoFan is an awesome cooler, I want one badly.

Perfect fit for mITX !

If it wasn't too big.

Nothing an HDPlex riser couldn't solve while being inline with the color scheme.

 

[confusis]

It seems the heatsink you've used here might blur the test results a bit. It's top face is nearly quadratical, so the difference between airflow from the front or the side is going to be low, and the hole in the middle could allow for some kind of continuous airflow to form.

I did a similar test with some Arctic Cooling tower cooler and a 45W CPU, and that got up to 81°C under 100% load in horizontal orientation and started throttling. In vertical, it was at 72°C. Didn't test sidewards vs. frontwards airflow, though.

I was just testing with what I had to hand. Yes, the cooler appears to be symmetrical, however, Scythe does state that there is a specific airflow direction for this cooler. The internal structure is not just flat fins, the fins are somewhat different than the top plate - http://www.hardwareinside.de/wp-content/uploads/2015/10/close7.jpg

In saying that, the Ninja models were somewhat marketed with passive and semi-passive cooling in mind.

 

[confusis]

What's the reasoning behind this ? Because metals can be plated or even painted, so I'm not sure what the reason is.

Black is the best thermal body in terms of being a absorber or emitter - so even though a layer may be added to make the cooler the darker colour, the benefits of the heat emission may outweigh the losses from adding a layer of plating/paint.

I'm curious about the topic of passive cooling, some questions that I can think of:
- how much heatsink surface area would you need per 10W of heat ? (considering adequate heatpipes)
- would it be conceivable to cool a 200W GPU passively ?
- how much "airflow" does passive cooling generate at ~60°C with 20°C ambient ?
- what are the best performance per watt components for a completely passive gaming PC ?

- This would require testing that we don't have the equipment for unfortunately
- Yes it would, but it won't be SFF
- A noticeable amount - not enough to register on my $10 eBay anemometer, but enough to move a piece of paper held above the heatsink
- GTX950 (non pcie 6 pin) and an i5 T (lower power) processor