Research On Flow And Heat Transfer Characteristics Of Air Forced Convection Cooling System In Electronic Equipments

With the rapid development of electronic technology, the electronic equipments havebecome lighter, thinner, shorter and smaller, while the power dissipation is increasingrapidly. The air cooling systems are widely used in the electronic cooling equipments fortheir low manufacturing cost, convenience in the installation, high cooling efficiency andreliability. On the basis of desktop computers, an integrated model that involves the axialfan and heat sink has been built, according to the features of air cooling system in therestricted space. The mechanism of flow matching problem and cooling optimization hasbeen investigated, the matching method of the cooling system has also been provided.In this paper, a3-D numerical simulation study on the internal and exit flow behaviorabout the axial fan used in the cooling system at different operating conditions has beenconducted. The results showed that the internal flow patterns in the impeller were in goodcondition at low back pressures. With the increase of back pressure, flow separation hasbeen induced at the blade near the hub and middle of the blade passage. Meanwhile, thesecond vortex was strengthened near the blade passage near the fan frame. With thereduction of the effective outflow passage area, flow recirculation was induced inside themiddle blade area. The flow was shown to be complex with significant radial and tangentialvelocities and regions with little or no flow. The outflow diffuse phenomenon was notobvious at low back pressures while the outflow axial jet angle increased with the increaseof back pressure.On the basis of integrated model, the mutual mechanism between the flow and heattransfer has been investigated. The research showed that the integral performance of thecooling system was up to the whole flow field and the heat exchange characteristics of heatsinks. The optimized angle of the fin can lower the loss when cooling air attacking the heatsink at the inlet. With the increase of the thickness of the fin, the flow passage can beblocked. At the same time, as the fin thickness growing down, thermal resistance ofconduction grows up. The conclusions have been provided, which the inclined angle of thefin and the fin thickness had the most optimized value. The best values are up to the cooling flow and heat exchange area. The cooling flow usage ratio has been improved by elevatingthe outer fin at the axial direction.Finally, the mechanism of heat transfer enhancement in the air cooling system hasbeen discussed on the basis of wavy-fin and cavity-fin in the heat sink. The results showedthat the right method can advance the flow near the fin wall and improve the heat transferon the fin surface.The present work is financially supported by the Central University Special FundBasic Research and Operating expenses under the grant No.2011QN156.