Re: Airflow direction in rack-mount cases

On Sat, 28 Jun 2008 20:57:48 -0700, StickThatInYourPipeAndSmokeIt
<Zarathustra@xxxxxxxxxxxxx> wrote:

On Sat, 28 Jun 2008 17:22:07 -0700, John Larkin
<jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

On Sun, 29 Jun 2008 09:18:37 +1000, "Phil Allison"
<philallison@xxxxxxxxxx> wrote:


"Allan Herriman"

Hi, I'm aware of some standards that dictate airflow direction in rack
mount cases (e.g. ETSI 300 119 and NEBS), and it's usually front to back,
bottom to top, or (least preferred) left to right.

But recently I noticed some equipment from Brocade in a 1U case that drew
air in at the back, and blew it out the front. This is actually mentioned
in the datasheet, so it was not an assembly error (with the fans in the
wrong way around).

Why would designers go against the standards and do this? Could there be
some benefit to the equipment?


** For the most effective cooling, fans need to blow into an enclosure and
directly onto the hottest parts - ie all the heatsinks fitted to semis.

In the world of professional audio power amplifiers (where dissipations can
exceed 1kW per amp), the front panels are mostly used for user controls and
displays which leaves little room for any fans - so they wind up at fitted
back along with the in /out and AC supply connectors.

The result is that " back to front cooling" is the pretty much the norm -
though examples of the reverse exist and also back to dual side outlet
cooling too.

The worst idea out is " bottom to top cooling" - cos although this the
way air likes to flow and seems intuitively correct what you inevitably get
with a rack full of such amplifiers is the internal temperatures rising
alarming from bottom to top as well - since each amp is supplied with the
heated air from the ones below !!!!



..... Phil







Here's a power amp with front intake, rear exhaust, and fans in the
middle. Something to offend everybody.

With the difference being that there are no heat producing elements in
the front section of the module.


The blue heatsink in the front has 32 300-watt power fets on it, clamp
mounted to copper heat spreaders. This is an MRI gradient amplifier,
about 17 KW peak power output.



ftp://66.117.156.8/L500_Front.jpg

ftp://66.117.156.8/L500_Side.jpg




PVC wiring, And it actually has side exhausts.

More on the back.

John


.

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