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Millions of DVRs (digital video recorders) are sold each year,
and getting a new design to market quickly can have a major impact
on product revenue. In one unit the number of parameter permutations
made it impossible to optimize the thermal design using traditional
methods while still meeting the customer's project schedule.
The goal was to maximize reliability by delivering the incoming
cool air to the hard drive, then directing it to the hottest
components, and finally to the remaining electronics. We separated
the hard drive from the electronics by surrounding it with a sheet
metal wall and then mounted the fan on the downstream side of the
wall (see Figure). This reduced noise by placing the fan
inside the housing, and drew air from the hard drive section to cool
the electronics.
While there were a few limitations (mostly because of cabling),
essentially the fan could be anywhere in the divider wall, the
intake and exhaust vents could be located on any of the six sides of
the enclosure, and the electronics and hard drive could be
positioned anywhere on their respective sides of the divider wall.
We calculated approximately 60 Coolit models, studying the impact of
component placement, whether the fan should blow from left to right
or from front to back, checking to make sure hot air from the power
supply wasn't drawn toward the hard drive, and optimizing vent sizes
and locations.
In the end, we found more than one design parameter
combination that met the specifications and were able to supply the
customer with several workable designs from which to select based on
manufacturing costs, aesthetics, or other criteria.
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