[Beowulf] materials for air shroud?

Gus Correa gus at ldeo.columbia.edu
Fri Sep 16 07:54:32 PDT 2011


mathog wrote:
> A not so short story about air flow...
> 
> Yesterday I did some experimenting with different baffles and ducts, 
> each built temporarily
> out of the cardboard backs from yellow notepads and held together with 
> masking tape.  (Not worried
> about a fire, since it only ran for 10 minutes at a time like that, and 
> I was right there to
> yank the plug and rip out the cardboard if something went wrong.)  The 
> system has a Supermicro H8DC8
> motherboard in a Supermicro case.  This one:
> 
> http://www.supermicro.com/products/chassis/2U/823/SC823S-550LP.cfm
> 
> This is what that motherboard looks like without heat sinks:
> 
> http://www.supermicro.com/a_images/products/Aplus/MB/H8DC8_spec.jpg
> 
> and here is a very similar motherboard with heat sinks in place (but 
> not my
> motherboard, which uses conventional flat passive heat sinks, not the 
> big curved
> orange monsters in the picture).
> 
> http://i19.photobucket.com/albums/b165/TeamScream/Wide-2.jpg
> 
> Notice the 50% overlap in the heat sinks in the direction of the 
> airflow?
> That is the overlap with more conventional heat sinks too. Yes, it 
> really
> does feed hot air from CPU1 into CPU2.   Putting a little wall in,
> redirecting the hot air from CPU1 around CPU2 dropped CPU2's 
> temperature
> by 4C.  Nothing else I tried made a bit of difference - including 
> lowering
> the "ceiling" over CPU2.  CPU2 is still hotter than CPU1 even with that
> fix.  The reason it will not get any better is that while there are 4 
> fans
> in the system, they are not placed very well for this motherboard.  The
> first one sends all of its air into the PS and so doesn't cool the CPUs
> at all.  Totally a waste since the PS has a fan already.  The next fan
> is partially blocked by CPU1, so maybe 3/4 of its air is available for 
> CPU2.
> CPU1 then gets the remaining 1/4 of that fan, and most of the next fan,
> so around 1 whole fan's worth.  The last fan blows over the chipset and
> PCI slots, again, with no contribution to cooling the  CPUS.
> 
> For comparison, here is a Rio-works  HDAMA motherboard which we have.  
> For
> this design airflow was taken into account.  Note that the CPU sockets 
> are
> spaced farther apart perpendicular to the air flow.  It is very similar
> hardware otherwise:
> 
> http://www.opteronics.com/images/16a_MBLarge.jpg
> 
> there are some pictures of these with heat sinks in place which may be 
> found
> by google image search for "HDAMA motherboard" - I didn't want to link 
> to them as they
> all seem to be on ebay and those links could disappear at any time.  
> Note how the
> heatsinks do not overlap in the direction of the air flow?  We have one 
> of these,
> with passive heatsinks of approximately the same shape, but a bit 
> taller,
> stuffed into an old 2U case scavenged from an old machine.  In that 
> machine
> the two CPUs run at very close to the same temperature.  The component 
> layout
> in the case is very similar to the Supermicro except that the heat 
> sinks are not
> overlapping, so here there is a fan lined up directly on center with 
> each CPU,
> plus one to cool the chipset/PCI slots.  The PS gets by on its internal 
> fan.
> The old case has been "optimized" for air flow by the simple expedient 
> of placing
> the 3 fans as just described (originally there was just one fan in it), 
> plus
> removing the front panel and as much of the back panel as possible, 
> including
> the shield that normally goes around the jacks on the motherboard.
> 
> The HDAMA machine is pretty darn ugly, but it definitely "breathes" 
> better than
> the Supermicro.
> 
> I found a product with the perfect properties for sticking 
> polypropylene sheets
> together.  This is 3M "Jet-melt" 3731 hot melt adhesive.  (Also called 
> "Scotch-Weld").
> Unfortunately I need about 2cc of it, but nobody sells it in sizes less 
> than 11 pounds!
> The only place that sells anything in this whole 3M hot melt line as 
> single sticks is Digikey,
> and the one they sell
> 
> http://parts.digikey.com/1/parts/440266-hot-melt-adhesive-vo-5-8-x2-3748-vo-tc.html
> 
> is not as heat resistant as the 3731.  Probably have to use 3748 
> though, since at least
> it can be purchased easily.
> 
> Regards,
> 
> David Mathog
> mathog at caltech.edu
> Manager, Sequence Analysis Facility, Biology Division, Caltech
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Hi David

It may complicate matters too much, but to avoid blowing warm
air over CPU2 on the SuperMicro board, is it possible to make two ducts,
slightly S-shaped ( __/``` ), one blowing air on the (cpu-1-RAM)+CPU2,
the other on CPU1+(cpu-2-RAM)?
Or perhaps a single duct, but include an S-shaped wall/divider between 
the two?

Gus Correa


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