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

Size of the vent openings

(g) (o) 2 openings + 1 additional opening

closed open

Other parameters of the study

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

Ra = 2.2x106 Ra = 2.2x106

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

H

W

Tw

q=0

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

Schlieren technique

Focalfilament

Colour bandsfilter