[Beowulf] Innovative liquid cooling

Prentice Bisbal prentice.bisbal at rutgers.edu
Mon Mar 4 07:16:26 PST 2013


Thanks for the the additional details. You addressed all of my concerns. 
I wish the original article had these details. Unfortunately, I think 
the original article simplified things a bit to much, and was a bit 
optimistic about running one of these in a dessert.


On 03/01/2013 05:46 PM, Jörg Saßmannshausen wrote:
> Hi all,
> answers are inserted.
> On Donnerstag 28 Februar 2013 Prentice Bisbal wrote:
>> On 02/28/2013 05:00 AM, Hearns, John wrote:
>>> I think this has been discussed here before, but it is a pretty
>>> innovative product:
>>> http://www.theregister.co.uk/2013/02/28/wet_servers_cut_cooling_costs_res
>>> earch_leeds_university/
>> I really should just save my rants about immersive liquid cooling on a
>> web page somewhere so I can just provide a link every time this topic
>> comes up. I'd just provide links to my previous rants here in the
>> archives, but I'm feeling lazy this morning.
>> Seriously, this article is both interesting and confusing, and there are
>> some stupid/ridiculous statements in the article.
>> 1. The interesting:
>> How easy is it to clean this liquid up? Is it oily like mineral oil? If
>> it's not slippery and it's easy to clean up, that addresses my biggest
>> problem with immersive cooling. The Novec didn't look as thick or
>> slippery as mineral oil in the video, but it's hard to tell something
>> like that from a web-quality video.
> It evaporates easily and it is used as a cleaning agent.
> You can dip your mobile into it and it is still working (the mobile, that is).
> When you fish it out again you got a clean mobile. You might be surprised how
> much grease there is on a mobile ;-)
> So it is not like oil, the visosity is lower.
>> 2. The confusing:
>> Is the Icetope system an immersive cooling system? From the video, it
>> looked more like a "direct contact" cooling system where the liquid is
>> run through pipes into "direct" contact with the processors, but the
>> demo made me think they are talking about immersive cooling. Even for
>> direct-contact cooling (if that is the right term) having a
>> non-conductive liquid is a better option than water if a leak occurs.
> Yes. Motherboard is imersed into the Novac in a sealed Aluminium container
> which got a chilled plate on one side. The chilled plate is cooled with water.
> So for that you need a pump. The excess heat is removed by an outer loop water
> cycle. Here you can use whatever you like, even grey water (with a filter). We
> want to use 3 radiators so here we need a heat-pump, the same you get from
> your local DIY store for your domestic central heating. Not much noise here.
>> 3. The stupid/ridiculous:
>>> Dunking servers in new magic liquid 3M Novec reduces the cooling
>>> system's energy use by 80 - 97 per cent, compared to cooling systems
>>> that use air. Air cooling is inefficient because it is a poor
>>> conductor, produces diffuse general heat and requires energy-chomping
>>> high powered fans, said the boffins.
>>> 3M Novec is also a thousand times better at conducting heat than
>>> water, and one low-powered fan in a chamber of 3M Novec is adequate toJorg,
>>> Thanks for the the additional details. You addressed all of my concerns.
>>>   i wish the original article had these details. Unfortunately, I think
>>> the original article simplified things a bit to much, and was a bit
>>> optimistic about running on of these in a dessert!
>>> chill a server array.
>> At some point or system size, you're still going to need pumps to
>> circulate the liquid. While natural convection is fine for gases, it's
>> usually inadequate for liquids due to their higher viscosity. And if you
>> need to transport that liquid horizontally away from the heat source to
>> the heat sinks, you're definitely going to need pumps. Liquids might
>> have thermal capacities and thermal conductivities that are about 1000x
>> that of air, but I think the viscosity of a liquid has got to be at
>> least 1000x that of a gas. In this case, the pumps are still probably
>> using less electricity than all those fans, but I think these quotes
>> distort some of the facts.
> See above. The novac will not be pumped around, convection is all you need.
> Remember, the nodes are standing upright and are not flat as a normal
> installation would suggest. So the transport is vertically and here you got a
> 'chimney effect' as well.
> So, as mentioned above, you need two sets of pumps for the inner and outer
> look of the water (sic!) cooling system.
>>> The fact that this system is completely enclosed raises a host of
>>> possibilities. It does not interact with its environment in the way an
>>> air-cooled server does, so you could put it in an extreme environment
>>> like the desert
>> Ummm, no. that heat still has to go somewhere. And that "somewhere" has
>> to be at a temperature low enough for there to be a temperature
>> difference large enough create the "driving force" necessary for useful
>> heat transfer. That's probably not going to happen in the desert.
> The outer water cycle has a max. temperature of 50 °C and the return is max 45
> °C. Given it is cold in a dessert at night you might be able to just about do
> that. However, I would not really want to have my cluster in the dessert ;-)
>>> It is also completely silent. You could have it on a submarine or in a
>>> classroom.
>> See my earlier comment about the need for a pump. I guarantee that even
>> the smallest production systems will need some kind of circulation pump.
>> you can probably locate that pump further away from the system being
>> cooled, but it will be producing some level of noise, somewhere.
> Think about how noisy a domestic heat pump for your central heating is and you
> get an idea how loud the cluster is. I stood next to one and you could barely
> hear it. So no big pumps.
>> Overall, if this 3M Novec overcomes the drawbacks of mineral oil, this
>> is great, but I feel that this article and this research is more like
>> press release for 3M Novec.
> Well, 3M is supporting the project. However, to be honest, of all the systems
> I have seen so far that seems to be the most intelligent one, specially as you
> can harvest the heat and do something with it.
> The radiators we are using are too small to heat up the building or the
> staircase in the winter, granted. However, it is more to demonstrate the
> principle and I only get one rack. I will post my experiences when and if I
> get the system installed. At least so far nobody here mentioned a serious
> problem which is reassuring.
>> Rant over. You may now return to your regularly scheduled work day.
> Not a rant, just some comments :-)
> All the best from a dark London
> Jörg


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