HEAT TRANSFER FROM AN ELECTRONIC MODULE PLACED DOWNSTREAM OF A FENCE

Abstract

The present work investigates experimentally the heat transfer and flow characteristics for an electronic module mounted on a simulated printed circuit board placed downstream of a fence on the bottom wall of a duct with an aspect ratio of 4. The module height (B) to channel height (H) ratio is fixed at B/H=0.317. Three different values for the fence height (b) and four values for the spacing between the fence and the module (S) were investigated in such a manner that the ratio b/B=1, 1.5 and 2, and the ratio S/B=1, 2, 3, and 4. Reynolds number, based on the streamwise length of the module (L), was ranged from 8000 to 40000. The results for the module without fence displayed some noticeable differences as compared to the smooth duct flow due to the existence of the separation-reattachment flow patterns. Secondary vortex tubes were existed at the module sides due to the presence of the fence and these vortices have significant effects on both the heat transfer and flow friction. Both Nusselt number and Fanning friction factor are strongly dependent on Reynolds number while they are critically dependent on both the fence height and spacing. A maximum Nusselt number enhancement ratio (Nu/NuN_F) of about 1.94 was obtained corresponding to a friction factor ratio (F/FN_F) of about 6.62 at the condition (Re=8700, b/B=1 .5 and S/B=2). It was found that the fence with b/B=1 provides the best performance based on the criterion of equal mass flow rate. New correlations were obtained for the average Nusselt number and the Fanning friction factor utilizing the present measurements within the investigated range of the different parameters.