Natural
Convection in a Telecommunications Exchange System |
|
The system shown is naturally ventilated and consists of six sub-racks
mounted vertically. Each sub-rack contains 15 PCBs with 1" spacing,
and the total power dissipated is 646 Watts. The front door of the enclosure
is perforated at three levels to allow ambient air to enter. The roof
is also perforated to allow the heated air to leave. Angled baffle plates
are placed between sub-racks 2 and 3, and between sub-racks 4 and 5, so
as to ensure that fresh, ambient air is introduced at these points. Flomerics
were supplied with the above problem definition by a major European telecommunications
equipment manufacturer, and were asked to simulate the problem without
prior access to the measured results. A comparison of predicted and measured
data showed good agreement (see Table), and convinced the company concerned
to license the software for application in future projects.
Results
 Air
temperature measurements were made at four different horizontal locations
in between the PCBs identified as Slots 5, 8, 10, and 13. The measurements
were then repeated for vertical locations at the top of each of the six
sub-racks.
|
Temperatures
in °C
|
| SUB-RACK |
1
|
2
|
3
|
4
|
5
|
7
|
SLOT
5
Experiment FLOTHERM |
41.0
43.4
|
33.5
34.1
|
43.3
44.3
|
31.8
33.4
|
35.0
33.4
|
27.6
27.4
|
SLOT
8
Experiment FLOTHERM |
43.0
43.3
|
35.3
33.4
|
44.5
44.5
|
33.5
32.8
|
34.0
35.3
|
26.7
27.4
|
SLOT
10
Experiment FLOTHERM |
40.0
42.5
|
36.6
33.0
|
44.5
43.7
|
33.5
32.5
|
34.0
35.3
|
26.7
27.4
|
SLOT
13
Experiment FLOTHERM |
36.8
35.0
|
31.8
27.3
|
36.8
37.7
|
28.8
26.9
|
36.1
39.8
|
28.6
32.1
|
Note that the most critical chimney effect
is in slot 8 which is the hottest.
|
|
|
|
