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With the introduction of embedded mesh technology, Coolit has
dramatically reduced cell counts making it possible to model
complex systems and boards that were impossible to model before
without resorting to simplifications. It has eliminated
dependence on approximate model building techniques, such as
resistor networks and lumped parameter (compact) models, and
has significantly reduced calculation times over existing
approaches.
Coolit v. 5.00B with embedded mesh technology was used on two
projects. The first was a 250 W military computer by a major
avionics manufacturer designed for the F-16 aircraft. The
aluminum chassis exterior was cooled by natural convection and
radiation, while the interior was cooled by a plate-fin heat
exchanger consisting of 31 horizontal fins mounted on each side
of the chassis. 12 VME cards were fastened to the heat
exchanger and the assembly was cooled by 4 deg C air entering at 4.3 CFM.
While the heat exchanger was modeled in detail, the VME cards had to be
modeled using lumped parameters in order to fit the
problem within the maximum allowable 2 GB RAM. Performing this analysis at
the card level (no components) required approximately 600,000
cells and took almost 6 hours to run. When the analysis was
performed using lumped parameter models of some of the
components, it required 1.5 million cells and took 10 hours.
This analysis was repeated using embedded mesh technology. Two VME
cards were detailed down to the die level, while the remaining cards
were modeled using lumped parameters. Such a model would have required
6-7 million grid cells with a single grid. It now took only 770,000
cells, which could be solved readily on a computer with less than a
gigabyte of RAM. Because the components were modeled to the die level,
it eliminated the uncertainty of compact models, and the analysis was more accurate.
The second project was a 19 inch wide, 2U telecom chassis designed for
Avaya Communications. The system contained two main PC boards, 3 stackable
cards and a power supply. It was cooled by three fans providing up to 35.3 CFM.
The detailed thermal model included pin fin heat sinks and several PBGAs down
to the die level. The TO263 power diodes, including their heat sinks,
were also modeled in complete detail. If all the PBGAs had been modeled,
it would have taken about 10 million cells, which would have been
impossible to calculate due to RAM limitations. Using embedded mesh
technology, the same unit could be fully modeled
with different grid zones with less than one million
cells.
In both applications, Coolit easily resolved the multi-scale models
accurately without resorting to approximations of compact models.
The length scales ranged from almost a meter (chassis size) down to a
micron, all within the same model, a feat not possible with other CFD
software.
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