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Embedded mesh shrinks thermal models and eliminates approximations.

Courtesy of Avaya Communications and CAS Ltd.

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.

Military computer designed for the F-16 aircraft.
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Coolit model of computer (inset shows PBGA chips modeled to the die level and will all balls).
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Telecom chassis designed for Avaya Communications.
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Coolit model of telecom chassis (inset shows a zoom in of a PBGA).
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