is the enemy of electronics. While design engineers probably thought they were
going to be able to say goodbye to heat problems when they traded vacuum tubes
for transistors half a century ago, in fact, heat problems are here to
stay.† For one thing, while solid state
devices might not emit much heat in relative terms, when they are combined in
the tremendous densities found on chips - and in the packed circuit boards and
enclosures of today, they produce a lot of thermal energy. What's more, they
are often very sensitive to temperature excesses so they need protection. In
fact, in years past, some mainframe computer makers even resorted to running
chilled water through their enclosures.
though, the big challenge is to simply develop a better understanding of heat
challenges and then apply the right improvements to air flow to regain control
over the "heat monster."
instance, while wide ribbon connectors, which used to be one of the impediments
to clean air flow, are largely a thing of the past in most equipment, new
challenges have emerged. For instance, the popularity of PCI Mezzanine cards
(PMCs) is causing problems because they protrude into space that could formerly
be counted on for maintaining air flow. †Heat sinks have also gotten larger and more
in fact, any look at a typical enclosure will often reveal that there are in
fact innumerable other impediments to smooth and even air flow.† Some of this, of course, can be addressed in
the design phase, by making air flow a consideration from the start.† Fan placement and power are also
important.† Most cooling systems, for
instance, try to take advantage of the elementary principle that warm air rises
- so ambient (and presumably cooler) air is taken in at a low point in the
enclosure and warmer air is exhausted near the top.
fans appropriately is also important. Fans that have low capacity may not be
able to maintain necessary airflow when confronted with the many obstacles presented
within the enclosure.† In fact, larger
scale air handling equipment designers have rules of thumb regarding the number
of turns and the total distance air must travel that help them appropriately
size fans and ducts to room and building requirements.† To date, no one has come up with similar
rules of thumb for enclosures so common sense and experimentation may be the
don't assume that just because a fan has a higher rating (more cubic feet per
minute) that it will actually deliver better cooling. That's because typical
fans don't provide much pressure. So, when they are, in effect, funneling air
into an area that is blocked by components and characterized by twists and
turns, there's no guarantee air flow will really improve.
fact, in enclosure applications a fan with twice the air flow might only
deliver a 50 percent increase in airflow.
in short, it's cool to keep your enclosure cool. However, achieving that state
takes some real engineering effort.†
Reconsider component placements, look for opportunities to open up air
flow to and from the outside, consider ways to avoid dust contamination (a
challenge in actual operation, over time), and, of course, look for appropriate
fan characteristics.† Recent advances in
fan designs have helped to overcome some of the challenges described here.
Check with your fan vendor's technical support department for advice on
handling thermal challenges as well as suggestions on optimized fan/enclosure