在強制衝擊氣流下多孔質熱沉對矩形發熱元件散熱增強之研究

近年來，由於電子產品快速發展，相對電子元件總發熱量越來越高，如何能尋求有效地增強元件散熱方法來確保電子設備已成日趨重要。由於多孔性介質能增加流體的混合且提供較大的熱傳面積，在熱傳增益上效果顯著，經常被用於電子元件之散熱機構。本研究目的即探討在強制衝擊氣流下，多孔質熱沉對矩形發熱元件列之散熱增強效果分析。研究方法為以數值模擬分析於穩態衝擊流下，水平流道中內具多孔質熱沉之矩形發熱元件的熱流場分佈及其熱傳特性，並藉由改變各項參數變化，包括達西數Da、雷諾數Re、入口距底板之通道高度H*、噴流入口之寬度B*、熱源之間距Ss*、多孔質熱沉之熱傳導係數Rk和多孔質熱沉之高度Hp*，來分析其對流道內熱流場變化及元件散熱增強的影響。文中純流體區內遵守Navier-Stoke方程式，多孔材質區內之動量方程式則採用Darcy - Brinkman - Forchheimer modle 方程式。再配合介面及邊界條件，以流線函數-渦度轉換公式解上述複合層熱流場之聯立方程式組。數值模擬分析結果顯示，因衝擊氣流撞擊直接撞擊多孔質熱沉的影響，使第一塊熱源塊上表面散熱效果較差，其後熱源塊因受多孔質影響導致流場發生扭曲變化及發熱元件間形成循環渦流，而此循環渦流強度愈強，相對伴隨著熱傳量亦愈高，對發熱元件之散熱冷卻有增強效益，且此增強效益會隨著雷諾數Re、熱傳系數Rk和熱源之間距Ss*和多孔質熱沉高度Hp*增加而增加，但隨達西數Da、噴嘴入口之寬度B*及通道高度H*減少而增加。對於第一塊熱源塊而言，將發現有個相反趨勢，由於衝擊氣流直接垂直撞擊上表面，造成流體的阻力更高。

關鍵字

衝擊式氣流；多孔質熱沉；對流散熱；達西數

並列摘要

Recently, the rapid development in the design of electronic packages has led to increase the heat of electronic components. Therefore, the problem of efficient heat removal from electronic equipment is increasingly importance to ensure reliability of operation. The porous medium is usually used as augmented-heat-transfer tool in electronic cooling due to the high ratio of surface area to the volume in the heat transfer process and the enhanced flow mixing caused by the tortuous path of the porous matrix, in the thermal dispersion process. The purpose of this study is to explore the cooling enhancement from heat blocks by using porous heat sink under a single impinging jet. In this work, a numerical study was carried out for enhanced heat transfer from porous-mounted heat blocks in a horizontal channel by steady impinging jet. The flow field is governed by the Navier-Stokes equation in the fluid region, and the flow through the porous medium is governed by the Darcy-Brinkman-Forchheimer equation that account for the effects of the impermeable boundary and inertia. Through the use of a stream function-vorticity transformation, solution of the coupled governing equations for the porous/fluid composite system is obtained using the control-volume method. In addition, the dependence of streamline, isotherm, and enhanced heat transfer rate on the governing parameters defining the problem are examined in detail. The numerical results of this investigation show that the rectangular porous-covering block array changes the incoming impinging velocity field considerably, resulting in the distortion of streamlines and the formation of vortices zones between the blocks. The higher the transverse height of these vortices is, the larger the enhanced heat convection on the second and subsequent blocks is. This enhanced effect increases with Reynolds number Re, spacing between blocks Ss*, and conductivity ratio Rk, and the height of porous heat sink Hp*, but decrease with Darcy number Da, slot width B*, and channel height H*. For the first heat block, an opposite cooling tendency is found due to the core fluid impinges vertically to the top surface, which in turn offers a higher degree of obstruction to the flow.

並列關鍵字

Impinging jet ； Porous heat sink ； Convective heat transfer ； Darcy number

參考文獻

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[5] K. Vafai, and C. L. Tien, “Boundary and Inertial Effects on Convection Mass Transfer in Porous Media,” Int. J. Heat Mass Transfer Vol. 25, pp 1183-1190, 1982.

[6] M. Kaviany, “Laminar Flow Through a Porous Channel Bounded by Isothermal Parallel Plates,” Int. J. Heat Mass Transfer, Vol. 28, pp. 851-858, 1985.

[7] H. A. Hadim, and A. Bethancourt, “Numerical Study of Forced Convection in a Partially Porous Channel with Discrete Heat Sources,” ASME J. Electronic package, Vol. 117, pp. 46-51, 1995.

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在強制衝擊氣流下多孔質熱沉對矩形發熱元件散熱增強之研究

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