DIPTEM, University of Genova, Italy Cooling of an electronic board in a vented cabinet: heat...
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Transcript of DIPTEM, University of Genova, Italy Cooling of an electronic board in a vented cabinet: heat...
DIPTEM, University of Genova, Italy
Cooling of an electronic board in a vented cabinet: heat transfer performance and air flow visualization
Mario Misale, Giovanni Tanda
Thermal Issues in Emerging Technologies, ThETA 1, Cairo, Egypt, Jan, 3-6th 2007
Description of this work
Natural convection heat transfer in a vented cabinet is experimentally investigated
The cabinet consists of a rectangular, partially open, cavity in which a vertical isothermal plate, simulating an electronic board, is placed.
Experiments were conducted varying
the spacing between the plate and the cabinet walls
the location and size of the cabinet openings,
the thermal conductivity of the cabinet walls
Local and average heat transfer coefficients were measured by means of the schlieren optical technique
Geometry of the cabinet
Cabinet size: Hc=0.16 m, Lc=0.53m, Wc=0.02-0.052 m
Heated plate size: H=0.1 m, L=0.5 m, D=0.01m
Experimental technique (schlieren)
Mirror M2
Mirror M1
Light source
Test section
CCD camera
Color filter P.C.
y
Average convective heat transfer coefficients
no vents
no vents
Plate without cabinet
no insulation
insulation
Local convective heat transfer coefficients
Local thermal gradients increase
W/H = 0.21, no insulation W/H = 0.05
No
insu
lati
onIn
sula
tion
Local convective heat transfer coefficients
W/H=0.05
Cabinet walls not insulated Cabinet walls insulated
Ra = 2.2x106 Ra = 2.2x106
Local convective heat transfer coefficients
x/H
0.0 0.2 0.4 0.6 0.8 1.0
Nu
0
10
20
30
40
50
60
70
ExperimentsSimulations
W/H=0.05, No side insulation, Tw-T=25 K, three lat.openings
Data processing
Rach(H’/W)3 > 20010 < Rach < 100000.05 < H’/H < 0.20.05 < W/H < 0.210.48 < H’/W < 4.0
Nu0 = (144/Rach2 + 2.873/Rach
0.5)-0.5 Cabinet wallsThermallyinsulated
Conclusions
Effect on h.t. performance of the cabinet aspect ratio (W/H): Negligible for W/H=0.21, moderate (=0.1), marked (=0.05)
Effect of thermal conductance of side walls:Very important only for W/H=0.05
Effect of opening size and number:For W/H=0.1-0.21, h.t.performance very close each to the others (except for the case (a) with the smallest opening height) and close to the performance of the isolated plate (without cabinet);For W/H =0.05, h.t.performance is markedly reduced as compared with the isolated plate results. The third additional opening affects the local distribution of h and only marginally the average h.t.coefficient
Majority of data with insulated walls are well fitted byliterature relationship for asymetrically heated vertical channels