Passive CPU Cooling - High Power CPU

[OAudio]

The time has come to deal with cooling of the c621 server I am working on. For the usual SQ and ambient noise reasons the server must to be entirely passively cooled. The cooling solution must deal with the heat dissipation requirements of a high power Xeon SP series CPU and it has to integrate into my server's quite dense packaging of power electronics in the area of the CPU. Of course there are no off the shelf passive cooling solutions for LGA 3647 socket CPUs 😦. 

 

Some time ago I posted details of the CPU cooling solution I had in mind.

 

 

On 7/13/2020 at 6:00 PM, OAudio said:

Hi All,

 

This is a rendering of one of the parts I'm making for packaging of my audio server development. There are a few final details to iron out with my engineerings but they will start cutting them from billet in the next couple of weeks with luck (waiting to get a production slot agreed). 

 

The cooler is designed to handle up to 200 watts of dissipation from an LGA3647. This is far higher than is required even for heavily loaded CPU. At 200w you would need a < 0.2C/w rated heat-sink which is a very large passive sink, but this is not really necessary for an audio server  ).

 

Care has been taken to make the heat pipes exit the CPU's footprint area 40mm above the motherboard. This means that  heatpipe routing remains simple and most sensible sized memory DIMMS should be insertable and removable without moving either the cooler or heat pipes. It can be reversed by 180 degrees when fitted meaning cooling pipes can exit over either bank of memory. I dont need this feature but it just seemed a good thing to do. End point clamps for the far end of the heatpipes are also being produced. Material will be engineering grade aluminium with clear hard anodizing to keep it looking pretty as time passes.

 

 

OAudio. 

 

 

 

 

As the server's design and packaging developed there were opportunities to refine the cooling design. The final CPU block design for instance no longer routes heat pipes out over the motherboard's RAM so it will be simpler fit. The block and clamps are produced now, they are CNC'd from billet and are pictured below with just anodizing is outstanding. 

 

 

 

 

Defiantly looking forwards to getting these fitted, I will update on how installation and testing goes. 

 

OAudio. 

 

  

[OAudio]

34 minutes ago, R1200CL said:

https://www.coolerguys.com/collections/intel-xeon-platinum-lga-3647/passive-cooler

http://www.akasa.com.tw/update.php?tpl=product/cpu.product.tpl&no=181&type=CPU coolers&type_sub=Low Profile&model=AK-CC9203

Hi R1200CL,

 

These are great coolers.

I use the Supermicro versions in 2u size. Unfortunatly they are not efficient enough to the cool 3647 cpus passively.  They are designed for server cases with fans and ducts to make sure the coolers see some forced air moving through them.

 

Whilst working on the server for the moment I am still using the Supermicro versions of these coolers with electrically isolated fans. It's far easier to strip and reassemble the server with the Supermicro 2U coolers than with the new CNC coolers and heat pipe system installed. 

 

OAudio.

[OAudio]

51 minutes ago, rossb said:

Is passive cooling really necessary? The fans on my Noctua NH-D15 are currently spinning at about 200rpm and are completely silent.

Hi Rossb,

 

There is a lot of dogma about fans which really makes me 🙂sometimes. You would think they are a complete disaster the amount of attention that "fan-less" setups get, however the truth is that if you: 

 

• run them slow so you are happy / can live with the with the sound noise levels,
• isolate them from the servers sensitive power (don't connect via the mother board headers),
• make sure that the fans ground is not referenced to the servers supplies,
• run fan wiring well away from the servers wiring and the motherboard etc,

the sound quality will be absolutely fine.

 

Sounds like a small auxiliary supply for your fans could be a good thing to try as well. 

 

Your fan setup is similar to the setup I am using to develop with here. The fans are electrically isolated from the server's power supplies for good measure. In a really high resolution system the set up is very good for sound quality, the impact of turning the fans off completely can just be heard but frankly its not much of a difference.

 

Last thought is that for DIY a passive heat pipe setup needs careful consideration. There are benefits in terms of physical sound levels from the server and "some" sound quality improvement to be had BUT you may lose the ability to easily move the motherboard from the chassis due to the complication of the pipe system. Not a problem ? possibly, but I need access to the motherboard to do "stuff" 🙂 which means its been in and out of the server 30-40 times at least.  

 

OAudio

 

 

 

 

 

 

     

[OAudio]

On 1/27/2021 at 5:12 AM, vhs said:

Hi there, any news yet ?

Hi VHS,

 

Thanks for the interest, yes things have moved forwards. I wanted to see  if the cooling system performed as per the thermal design I did. I couldn't wait any longer so I did do a trail fit a week ago. They are just about bang on the thermal design which was really nice to see  and they look absolutely superb in the chassis.  The coolers were made by an engineer with decades of work for a jet engine manufacturer, and it really shows. Its such a shame to shut them away inside the server chassis.

 

They are back out of the server again and the fans are back in for now for the access reasons I mentioned above.

 

Here is another picture of them with CPU mount attached.

 

OAudio.

 

 

 

 

[OAudio]

6 minutes ago, kyoya78 said:

 

I replaced one of the CPU coolers with my own (A7075). The thin fins are excellent for cooling but still have a negative effect on the sound. I was surprised at the improvement in sound quality even after replacing one of the CPU coolers.

 

 

Hi kyoya78,

 

What a difference to the radiator on the other CPU. 

That's a nice looking CPU block !

[OAudio]

On 2/20/2021 at 8:11 AM, vhs said:

https://wccftech.com/nvidia-geforce-rtx-3080-goes-all-passive-cooling-87c-temps-turemetal-up10-chassis/

 

GPU cooling is not a priority for the server builds I am working on, but the engineering of the GPU cooling system in the linked article looks really nice :-)