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Cool solutions for enclosures

Sooner or later, a design has to be enclosed and what form that enclosure takes is dependent upon the application.

With a consumer product, appearance is often one of the main purchasing influences. With an industrial product, aesthetic considerations may well be further down the list.
Dave Bowring, Rittal UK's product manager for electronic and outdoor products, said that 'enclosure' was a broad term. "Some will say 'box', others will say 'enclosure'. Some 'enclosures' are a rack framework with cladding, others are more like a cupboard with racks inside."
He pointed to a continuing decrease in product size. "In the overall scheme of things, products are getting smaller. The trade off is that as products shrink, designers want to include more functionality and that pushes product size back up again."
He gave the example of rack mounted boards. "There are probably a lot more people putting 1U or 3U units into a rack, where once they would have used 6 or 9U boards. Because of that, they are adding more of the smaller boards into the same volume to gain that extra functionality. And this is further complicated by designers adding mezzanine cards on some boards."
But Bowring believes one constant issue which designers have to deal with – no matter what shape the enclosure takes – is heat. "Designers are having to consider cooling at a much earlier stage than they would have done in the past. And Rittal is getting more and more requests for a total solution, including cooling."
There's a number of contributing factors here. Packing more processing power on to a board is one. Putting more boards into a system is another and making that system as small as possible is a further complication.
"When you cram more boards into a system, it becomes more difficult to push cold air through," he said. This is pushing companies like Rittal to provide more exotic enclosure cooling arrangements, including heat exchangers.
Martin Blake, managing director of Elma-Mektron, suggested that thermal simulation is now becoming an essential part of the enclosure selection and design process. "Systems with big processors and big boards require thermal simulation before getting into the overall design. Before, the approach was to look at the overall heat generated – say 400W – and decide a couple of fans was all that was needed. Once you get to systems such as ATCA, you have to take the approach of putting the 'hottest' board in slot 1 and then adjusting the air flow accordingly."
Andy Brind, Elma-Mektron's engineering manager, added: "While thermal analysis doesn't include the board design itself, it can help to identify where the hot spots would be. In fact, we've studied 296 processors to work out which run the hottest."
Blake said this approach was going down well with his customers. "They can predict where the heat problems will be – particularly when specifications change – and can then track more cooling to hot spots."
He believes thermal issues are now a design issue. "It has to be something you put into the original concept. In the old days, 21 slots of VME boards and two fans would be fine. Today, one or two boards can generate 500W."

Graham Pitcher

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