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 [email protected] Manager, Sequence Analysis Facility, Biology Division, Caltech _______________________________________________ Beowulf mailing list, [email protected] sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
