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_research_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.
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.
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 to
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.
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.
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.
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.
Rant over. You may now return to your regularly scheduled work day.
--
Prentice
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