HEAT TRANSFER AND FLUID FLOW IN METAL FOAM SUBJECTED TO OSCILLATING FLOW

摘要

The need for higher performance and an increased level of functional integration as well as die size optimization on the microprocessor leads to preferential clustering of higher power units on the processor. Conventional natural or forced convection cooling methods are not capable of removing such a high heat flux for maintaining a proper operational temperature. It is imperative to look for new methods of cooling the modern high-speed electronic components. The porous medium has emerged as an effective method of heat transfer enhancement due to its large surface area to volume ratio and intense mixing of fluid flow. Many researchers have studied heat transfer and fluid flow in a channel filled with metal particles or woven-screens. However, uni-directional flow through the porous channel yields a relatively high temperature difference along the flow direction on the substrate surface. For modem high-speed microprocessors, the reliability of transistors and operating speed are not only influenced by the average temperature but also by temperature uniformity on the substrate surface. Therefore, maintaining the uniformity of on-die temperature distribution below certain limits is imperative in thermal design. It is conceivable that oscillating flow through a porous channel will produce a more uniform temperature distribution, due to the presence of two thermal entrance regions for oscillating flow. In the present investigation, a novel porous material of open-cell metal foam was employed to study heat transfer and fluid flow of oscillating flow through a porous channel. The metal foam with fully inter-connected structure, large surface area to volume ratio and high permeability lends itself to applications in electronics cooling. This paper describes an experimental study on heat transfer and pressure drop behavior of oscillating flow through a channel filled with open-cell aluminum foam. Both cycle-averaged and length-averaged local Nusselt numbers were calculated to evaluate heat transfer rate of oscillating flow in metal foam channel. The effects of the dimensionless flow amplitude and frequency of oscillating flow on heat transfer were analyzed. A correlation equation of maximum friction factor of oscillating flow in metal foam was obtained and compared with the results for wire-screens obtained by other investigators under the oscillating flow condition. The results revealed that heat transfer performance can be enhanced substantially by oscillating flow through metal foam with moderate pressure drop.