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For a major Boeing avionics upgrade to the Air Force's C-130
aircraft, VT Miltope developed a digital mass storage system to collect
high-speed digital map and ground terrain data. The system consists of a
chassis-mounted processor, high
speed interface and sealed, removable hard disk drive. Design
requirements specified 10.1 psia air pressure and steady-state operation at 55C
with short-intervals up to 71C. For operator safety, equipment
surfaces could not exceed 11C above ambient air temperature.
The disk drive, which dissipates 16 W maximum, is cooled by a 102
CFM muffin fan that draws air from the front of the chassis.
Initially, the design was based on a standard drive cartridge, but
Coolit analysis indicated that the unit would overheat. To boost
heat transfer, VT Miltope engineers added cooling fins. While the
fins helped, they did not solve the problem. Using Coolit's flow
visualization capabilities, engineering discovered that much of the
air was bypassing the fins. To increase cooling efficiency, an air
duct was added to force the air through the fins.
The power supplies, processor module , server electronics, Fibre
Channel, and gigabit Ethernet chips were mounted via a thermal pad
to a custom aluminum heat spreader plate that sinks heat to the
chassis' aluminum right sidewall. Because of difficulties in
identifying actual power dissipation for the chips, Coolit analysis
was performed assuming maximum power dissipation, a worst-case
scenario. Even under these conditions, Coolit predicted component
temperatures would be below the maximum temperature specifications,
giving VT Miltope the confidence to proceed without prototype
testing. Released product testing validated this confidence.
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