Making electronic products smaller in size requires air passages in the products to be narrow. For effective thermal management with natural convection, the relationship between cooling performance and a space for the air passages must be clarified. In this study, the natural cooling capacity and flow field in relatively small electronic equipment have been investigated. A channel model was used as an experimental model of electronic equipments. The channel model has two vertical copper walls modeling the printed circuit boards and two transparent walls modeling the casing walls. The walls constitute a vertical channel with the height of 120mm, the depth of 56mm, and the variable width. The width of the channel is called “a wall clearance” here and it is varied from 5mm to 15mm. The copper walls were heated using electric heaters. Temperatures in the model were measured with thermo-couples. In addition, velocity distributions in the channel were quantitatively measured using a particle image velocimetry (PIV). The natural cooling capacity was obtained as functions of the wall clearance and heating power. Temperature rise of the heated wall showed small differences with the clearances of 10 mm and 15mm. However, when the clearance was decreased to 5mm, temperature rise increased. The relationship between Nusselt number and Rayleigh number obtained in this study agrees with those obtained for the parallel plates without side walls. The results of the velocity measurement revealed that the velocity showed a 33% decrease when the wall clearance decreased from 10mm to 5mm. On the other hand, the maximum velocity in the channel showed a 10% increase when the clearance decreased from 15mm to 10mm. The changes in the velocity profiles depending on the heating conditions are clarified.

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