A study of heat transfer enhancement for electronic packaging.

摘要

The fluid dynamic and heat transfer behavior of laminar non-Newtonian flow through non-circular ducts is of special interest because of their wide range of potential application in compact heat exchangers and in electronics cooling. The objectives of the present study were (1) to investigate the heat transfer characteristics for laminar forced convection of inelastic non-Newtonian fluids in a nonuniformly heated rectangular duct where the flow is hydrodynamically developed but thermally developing and (2) to investigate the influence of variable viscosity of temperature-dependent fluids on the laminar heat transfer and friction factors in a 2:1 rectangular duct. The governing equations were solved by a finite volume method. Second-order accurate differencing schemes were employed for both the diffusion and convective terms.;The effects of shear thinning, given by the Carreau equation, and the viscous dissipation, characterized by the Brinkman number, were examined via the friction factor, the Nusselt number, and the bulk fluid temperature. The results indicated that when viscous dissipation was present, the heat transfer from the heated surface of the duct was greatly enhanced with increased shear thinning of the fluid while the rate of increase of the bulk fluid temperature significantly decreased with axial distance. Consequently, the use of a shear-thinning non-Newtonian fluid for heat transfer enhancement appeared to be a very promising concept that is worthy of further study.;The present numerical results of local Nusselt numbers for oil (i.e., a temperature-dependent viscosity fluid) showed 70-80% enhancement over those of a constant property fluid and 40-50% enhancement over water, and gave excellent agreement with recent experimental results. The heat transfer enhancement from the heated top wall was due to an increased velocity gradient near the wall. A new correlation for local Nusselt numbers in the 2:1 rectangular duct was proposed which covered both thermally developing and thermally fully developed regions. Consequently, a temperature-dependent viscous fluid with a non-circular duct was proposed to be used in the design of a liquid cooling module for the computer industry.