1. 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

2. 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

3. Geometry of the cabinet Cabinet size: H c =0.16 m, L c =0.53m, W c =0.02-0.052 m Heated plate size: H=0.1 m, L=0.5 m, D=0.01m

4. Size of the vent openings (g) (o) 2 openings + 1 additional opening closed open

5. Other parameters of the study

6. Experimental technique (schlieren) y

7. Average convective heat transfer coefficients no vents no vents Plate without cabinet no insulation insulation

8. Local convective heat transfer coefficients Local thermal gradients increase W/H = 0.21, no insulation W/H = 0.05 No insulation Insulation

9. Local convective heat transfer coefficients Ra = 2.2x10 6

10. Local convective heat transfer coefficients W/H=0.05 Cabinet walls not insulated Cabinet walls insulated Ra = 2.2x10 6

11. Local convective heat transfer coefficients W/H=0.05, No side insulation, T w -T  =25 K, three lat.openings

12. Data processing H W TwTw q=0

13. Data processing Ra ch (H’/W) 3 > 200 10 < Ra ch < 10000 0.05 < H’/H < 0.2 0.05 < W/H < 0.21 0.48 < H’/W < 4.0 Nu 0 = (144/Ra ch 2 + 2.873/Ra ch 0.5 ) -0.5 Cabinet walls Thermally insulated

14. 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 by literature relationship for asymetrically heated vertical channels

15. Schlieren technique Focal filament Colour bands filter