Numerical analysis on forced convection enhancement in an annulus using porous ribs and nanoparticle addition to base fluid

Abstract

Miniaturization of electronic equipment has forced researchers to devise more effective methods for dissipating the generated heat in these devices. In this study, two methods, including porous media inserting and adding nanoparticles to the base fluid, are used to improve heat transfer in an annulus heated on both walls. To study porous media insert, porous ribs are used on the outer and inner walls independently. The results show that when porous ribs are placed on the outer wall, although the heat transfer enhances, the pressure drop increment is so considerable that performance number (the ratio of heat transfer enhancement pressure increment, P_N) is less than unity for all porous rib heights and porous media permeabilities that are studied. On the other hand, the P_N of cases where porous ribs were placed on the inner wall depends on the Darcy number (Da). For example, for ribs with Da=0.1 and Da=0.0001, the maximum performance number, P_N=4, occurs at the porous ribs height to hydraulic diameter ratios H/D_h=1 and H/D_h=0.25. Under these conditions, heat transfer is enhanced by two orders of magnitude. It is found that adding 5% nanoparticles to the base fluid in the two aforementioned cases improves the Nusselt number and P_N by 10%–40%.

摘要

电子设备的小型化迫使研究人员设计出更有效的方法来释放设备中产生的热量。在此研究中, 通过在基液中插入多孔介质和加入纳米颗粒两种方法, 以改善在两个壁面上加热的环行通道的传热 性能。为了研究多孔介质嵌入, 分别在内外壁上使用多孔肋片。结果表明, 当多孔肋片置于外壁时, 尽管传热增强, 但压降量相当大, 以至于所有研究的多孔肋片高度与多孔介质渗透性的性能参数 (P_N), 即传热增量与压降增量之比均小于1。当多孔肋片置于内壁时, P_N 取决于Darcy 数 (Da)。例如, 对于 Da=0.1 和Da=0.0001 的肋片, 最大性能数 P_N=4 出现在多孔肋片高度与水力直径比为 H/D_h=1 和 H/D_h=0.25。在这些情况下, 传热增强了两个数量级。结果表明, 在上述两种情况下, 在基液中加入 5%的纳米颗粒可使 Nusselt 数和P_N 提高10%~40%。