Background
Historically, empirical methods have been
used to analyze the cooling design of (COTS)
systems. However, the availability of
computational fluid dynamics (CFD) and heat
transfer (CHT) programs provides an
attractive possibility for minimizing prototype
testing. Although such programs have been in
existence for some time, their applicability to
complex electronic systems still needs
evaluation.
During the first year of this effort, studies
were performed to compare predictions from
both the CALCE software and Flomerics
Flotherm software with data for an existing
test vehicle. These studies involved
acquisition and reduction of measurements,
computer modeling, and comparison of the
results. A new test vehicle, constructed in
close cooperation with Loral, consists of a
COTS VMEbus chassis, configured to hold
twenty modules of the 6U type. Loral has
provided three mock VMEbus modules that
contain four distinct, separately wired
component types (308s, 220s, RPACs and
SRAMs). An additional seventeen thermofoil
heater equipped simulation modules were used
to fill the remaining slots.
Work Accomplished
All three test modules were wired with
strategically mounted thermocouples to
provide detailed component and front and rear
board surface temperature distributions. The
test vehicle was also modified to allow for
pressure drop measurements. Detailed
experiments have been performed on the test
vehicle which provide data to be compared
with Flotherm software models. The tests
were performed for flow rates ranging
between 105 to 210 ft3/min and module
power dissipation levels of 20.5 to 41 watts.
The inlet plenum for air flow caused large
recirculation regions, resulting in hot regions
on one side of the modules. These trends
were also confirmed by the Flotherm
simulations for this geometry. The
computational model was then modified to
investigate the effects of changes in the inlet
plenum shape on flow patterns and module
temperatures. A new shape was identified
that resulted in an improved flow pattern and
reduction in component temperatures. This
inlet plenum shape change was implemented
in the test vehicle, and resulting module
temperatures were measured.
