Enhancing forced convection heat transfer from multiple protruding heat sources simulating electronic components in a horizontal channel by passive cooling G.I. Sultan Mechanical Power Engineering Department, Mansoura University, Mansoura 35516, Egypt Abstract Experiments were conducted to study forced convection heat transfer in a small aspect ratio of multiple protruding heat sources in a horizontal channel with passive cooling. Perforated holes are arranged in the base of channel in a staggered manner in two rows between heat sources. Due to the increase of temperature between heaters, outside air is withdrawn naturally through the perforated holes. Effect of air entering through the perforated holes with different holes/open area ratios (b  0.0147, 0.0260, 0.0409, 0.0589 and 0.8017) on heat transfer characteristics is examined. It was found that the heat transfer coefficient was enhanced for all values of holes/open area ratio. Results also show that holes with b  0.0409 gives the best thermal performance for 376  Re  6170 while Gr  0:37 × 10 7 which are studied and the maximum enhancement in heat transfer is found to be 33.15% at Re  3428. The average Nusselt number and maximum dimensionless temperature are correlated as a function of the Richardson number Gr=Re 2  and the holes/open area ratio b .  2000 Elsevier Science Ltd. All rights reserved. Keywords: Passive cooling; Holes/open area ratio; Protruding heat sources 1. Introduction Air-cooling has been and still likely remains a promising option in the cooling of electronic equipment. The elec- tronic components “ICs” are usually mounted on boards, which form channels or cavities. Due to the progress of circuit interaction, heat dissipation is concentrated in fewer components while the system volume shrinks, thereby reduction the space for coolant flows. Conse- quently, unless an effective removal of the excessive heat generation within the device is in place, the perfor- mance of these sensitive electronic components deterio- rates rapidly. However, from an overall view of what has been accom- plished experimentally, it appears that such data is not suffi- cient, although noticeable efforts were mentioned. Aung [1] indicated through an experimental study that downstream of the step, the heat transfer increases monotonically in the streamwise direction. Gooray et al. [2] developed a numer- ical model (k – e ) for heat transfer in turbulent recirculating flow over two-dimensional (2D), rearward facing step and sudden pipe expansions. Hall and Pletcher [3] solved the boundary layer momentum and continuity equations in a coupled manner by a finite-difference numerical scheme and predicted separated flows region and predicted sepa- rated flow regions and heat transfer characteristics. Chan and Tien [4] investigated the laminar steady-state natural convection in a 2D rectangular open cavity. LePeutrec and Lauriat [5] obtained numerical solution for fluid flow and heat transfer rates for the 3D natural convection in a rectan- gular enclosures. Wadsworth and Mudawar [6] investigated through an experimental study, the single phase heat trans- fer from a smooth simulated chip to a two-dimensional jet of dielectric fluorinate FC-72 liquid issuing from a thin rectan- gular slot into a channel confined between the chip surface and nozzle plate. Kim and Anand [7] studied numerically, the 2D turbulent heat transfer between a series of parallel plates with surface mounted discrete blocks heat sources. Papanicolaou and Jaluria [8] presented a numerical simula- tion of turbulent transport from an isolated heat source in a square cavity with side openings. Hwang and Liou [9] studied experimentally the turbulent heat transfer and fric- tion in a low-aspect ratio rectangular channel in which two opposite walls are roughened by perforated ribs. Dehahan and Behnia [10] found through a theoretical study that the surface emissivity has been varied and its effects on the flow and thermal field has been determined for different values of Ra. Torii [11] performed a numerical study on unsteady Microelectronics Journal 31 (2000) 773–779 Microelectronics Journal 0026-2692/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S0026-2692(00)00058-6 www.elsevier.com/locate/mejo E-mail address: gisultan@mun.mans.eun.eg (G.I. Sultan).