|
CAS Ltd, Haifa, Israel successfully developed a thermal
management design for a Lucent Technologies
communication system, replacing a failed design provided by a
Massachusetts-based consulting company. The consultant, who had
used a competitor's thermal analysis software, had predicted
that no heatsinks were required on the system's optical modules.
CAS, using Coolit, determined that just the opposite was true,
and prototype testing proved that the Coolit analysis was
correct.
The original communications system shown in Figure 1 did not
specify heat sinks for the optical modules. The single card/slot
held two, 3 x 4 inch optical modules, three power supply
modules, plus some additional electronic components. Total card
power consumption was approximately 42 W, with the two optical
modules drawing 11 W and 14 W, respectively.
Since optical modules are the most temperature-sensitive
units in a telecom system, engineers must take particular care
to ensure they have a safe thermal environment. With a maximum
allowable case temperature of about 70oC, and inlet
temperatures of 55oC there is little margin for thermal
designers. Indeed, for the original design without a heat
sink, Coolit predicted, and an experiment confirmed that the 14
W optical module would reach an average case temperature of over
79oC.
Unfortunately, the modules occupied all but 6 mm of space
within the slot, so there was not enough room to mount a
standard heat sink above the module. So, CAS proposed two
cooling scenarios, one using a novel, low profile "winged" heat
sink and a second that combined the "winged" heat sink with a
base heat sink on the back-side of the modules.
Coolit analysis predicted that, in the first scenario, the
average module case temperatures would be 68.0oC and
70.5oC for the 11 W and 14 W modules, respectively, Figure 2.
Experiments verified this prediction by giving average case
temperatures of 68.0oC and 70.7oC (see Table below). With the base
heat sink added, Coolit predicted average case temperatures
would decrease to 67oC and 69oC. Flow ribbons and
temperatures are shown in Figure 3.
|
|
Coolit
Analysis (oC)
|
Experiment
(oC)
|
% error
|
|
11 W
module
|
68.0
|
68.0
|
0.0
|
|
14 W
module
|
70.5
|
70.7
|
0.3
|
After completing its final analyses, CAS successfully
delivered the thermal design to its customer. The customer,
impressed by how well the Coolit predictions matched test
results, felt that, at last, it had a thermal design on which it
could depend.
|
