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When NEC Computers Inc., Boxborough, MA tapped Coolit to accelerate
custom heat sink development for its new dual processors servers,
it landed an added and unexpected bonus-a breakthrough in heat sink
design.
The seeds were sown as NEC engineers analyzed Coolit models of
airflow movement and heat dispersion across elliptical pin fin designs.
A conventional elliptical pin fin design maintains a uniform cross-section
across its surface. Yet the animated Coolit models were clearly
revealing that cooling surface requirements were increasing as air
transversed the heat sink. To NEC engineers the fix was obvious:
reject conventional topographies and design heat sinks that match
the changing thermal demands.
Using Coolit, engineers manipulated base thickness, fin geometry,
airflow and the balance among these parameters in the search for
the optimum configuration. Four custom heat sink designs were evaluated
in only two days. The result was a patent-applied-for design in
which pin width and thickness vary to compensate for losses in cooling
capacity as air slows down and warms up during its heat sink traverse.
In addition, the pins are aligned in rows, unlike conventional designs
where they are staggered like bowling pins.
At the leading edge of the heat sink where airflow is maximum,
smaller pins deliver the required heat dissipation. The smaller
pins also reduce the likelihood of creating an air dam that would
reduce downstream cooling. As air moves across the heat sink, its
velocity decreases and the pin surface area is increased to compensate.
The unorthodox design shaves 15 deg. C off processor die temperature
and cuts the per-piece cost by over 80%. On top of these bonuses,
NEC engineers still reaped the original benefits they sought from
Coolit: weeks of savings in design, model building and testing time
worth thousands of development dollars.
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