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Coolit predicts flow inside a production computer chassis.

Courtesy of University of Texas.

In a project sponsored by Axxion Corp., a major manufacturer of personal computer enclosures and chassis, researchers at the University of Texas used Coolit to analyze the impact of various ventilation configurations on airflow within a desktop computer chassis. By creating the simulations, the researchers were able to alter the configuration without having to physically modify any units.

The default chassis layout has three vents; two in the front and one in the rear (see Figure 1). Because the rear vent is closest to the processor heat sink and fan, it is reasonable to expect that blocking this vent would result in reduced heat transfer from the processor and possible overheating. Using Coolit, however, it was found that this is not necessarily true (see Figure 2).

As can be seen in the figures, blocking the rear vent increased flow velocities through the front vents (greater spacing between arrows on streamlines). This results in better ventilation of the chassis as a whole and, therefore, reduced temperatures. In addition, the back vent flow was colliding with the front vent flow, creating a stagnation region near the processor. Blocking the back vent eliminated this stagnation region, further improving convection around the processor. Such counterintuitive insights are made possible by CFD simulations - no amount of prototype testing would obtain such detailed and quantitative data.

To verify modeling accuracy, Coolit flow predictions were compared to hot-wire anemometry measurements. Table 1 shows a comparison between predicted and actual maximum vertical velocity in the default chassis configuration.


Location

Measured Velocity (m/s)

Coolit  Predicted Velocity (m/s)

Percent Difference (%)

right side of heat sink

4.93

5.13

4.1

right side of power supply

4.01

3.71

-7.5

right side of power supply fan

2.96

2.85

-3.7

upper vacant vent

1.64

1.61

-1.8

Figure 1. The default chassis layout with three vents; two in the front and one in the rear.
in
Figure 2. The new chassis layout with two vents.
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