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On 02/28/2013 05:00 AM, Hearns, John wrote:<br>
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<p class="MsoNormal">I think this has been discussed here
before, but it is a pretty innovative product:<o:p></o:p></p>
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<p class="MsoNormal"><a class="moz-txt-link-freetext" href="http://www.theregister.co.uk/2013/02/28/wet_servers_cut_cooling_costs_research_leeds_university/">http://www.theregister.co.uk/2013/02/28/wet_servers_cut_cooling_costs_research_leeds_university/</a><o:p></o:p></p>
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<br>
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. <br>
<br>
Seriously, this article is both interesting and confusing, and there
are some stupid/ridiculous statements in the article. <br>
<br>
1. The interesting:<br>
<br>
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. <br>
<br>
2. The confusing: <br>
<br>
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. <br>
<br>
3. The stupid/ridiculous: <br>
<br>
<blockquote type="cite">
<p>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.</p>
<p>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.</p>
</blockquote>
<br>
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.
<br>
<br>
<blockquote type="cite">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</blockquote>
<br>
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. <br>
<br>
<blockquote type="cite">It is also completely silent. You could have
it on a submarine or in a classroom.</blockquote>
<br>
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. <br>
<br>
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. <br>
<br>
Rant over. You may now return to your regularly scheduled work day.
<br>
<br>
--<br>
Prentice<br>
<br>
<br>
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