結合強制脈衝衝擊流與多孔質熱沉用於電子元件之散熱增強分析

Analysis of Enhanced Electronic cooling by pulsating impinging flow and porous covers

陳柚良(Yu-Liang Chen)

指導教授 ： 黃博全

國立臺北科技大學/機電學院/冷凍空調工程系所/碩士(2012年)

https://doi.org/10.6841/NTUT.2012.00544

摘要

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。本研究目的即探討在強制垂直衝擊氣流下，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非穩態垂直強迫衝擊脈衝流下，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。文中純流體區內遵守unsteady Navier-Stoke方程式，多孔材質區內之動量方程式則採用transient 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。並藉由改變各項參數變化，包括達西數Da、雷諾數Re、振幅A、頻率St、入口距底板之通道高度H*、熱源之間距Ss*、多孔質熱沉之高度Hp*和多孔質熱沉之熱傳導係數Rk，來分析其對流道內熱流場變化及元件散熱增強的影響。
數值模擬結果顯示，(1)在穩定流下，多孔質熱沉之矩形發熱元件流場的劇烈變化將導致兩熱源體間產生循環渦流，並且多孔質熱沉後方循環渦流橫向高度提升將對熱源表面的散熱量產生顯著的提升；(2)在脈衝流下，在熱源體間的循環渦流週期性的變化將使得熱源體的右表面的熱傳增強效率有顯著的提升；(3)多孔質熱沉能有效提升遠離入口通道的熱源體熱傳增強效益。其熱源體的熱傳增強效益隨著振幅A、熱傳導係數Rk、熱沉高度Hp、通道高度H增加而增加，隨著雷諾數Re增加而減少。然而達西數Da、頻率St、熱源體間距Ss，並沒有呈現正比和反比的關聯，其熱源體的熱傳增強效益存在著一個臨界值，並呈現出極大(達西數Da)和極小值(頻率St、熱源體間距Ss)的現象。 (4)結合脈衝流與多孔質熱沉雖可提升流道內發熱源件之對流熱傳，但同時也須考慮所產生之壓損才有最佳的散熱效益。

關鍵字

衝擊脈衝流 ； 多孔質熱沉 ； 散熱增強

並列摘要

Recently, the rapid development in the design of electronic packages has led to increase the heat-producing capability of electronic components. Therefore, the problem of efficient heat removal from electronic equipment is increasingly importance to ensure reliability of operation. The purpose of this study is to explore the cooling enhancement from heat blocks by using porous heat sink under a single pulsating impinging jet.
In this work, a numerical study was carried out for forced pulsating impinging jet flow in a horizontal channel with multiple porous-covered heat blocks. The flow field is governed by the unsteady Navier-Stoke equation in fluid region, and the flow through the porous medium is governed by the transient Dacy-Brinkman-Forchheimer equation that account for the effects of the impermeable boundary and inertia. Solution of the coupled governing equations is obtained by utilizing a control-volume method through a stream function-vorticity analysis. The study details the variation streamline and cooling enhancement with the variation of different governing parameters, including the Darcy number, Reynolds number, pulsation amplitude and frequency, three geometric parameters,and conductivity ratio.
The numerical results show : (1)In steady flow, the porous-covering block array changes the incoming parabolic velocity field considerably, resulting in the formation of vortices zones between the blocks. The height of these vortices has significant effects on the heat transfer characteristics around the exposed faces of the blocks. (2)In pulsating flow, the periodic alteration in the structure of recirculation flow inside the inter-block region and behind the downstream block significantly enhances the heat transfer rate on the block right faces. (3) The heat transfer enhancement effect away from the entrance effectively increases by porous heat sink. This enhanced effect increases with pulsating amplitude A, conductivity ratio Rk, channel height H* and the height of porous-covering obstacle Hp*, but decrease with Reynolds number Re. However, the effect of Darcy number Da, Strouhal number St, and spacing of porous-covering obstacle Ss are not straightforward, and there exists a critical value for which the heat transfer enhancement factor is minimum (for Darcy numbers Da) or maximum (for Strouhal number St and obstacle spacing Ss). (4)The heated block with high-conductivity fiber porous-
covering heat sink subjected to forced pulsating channel flow is an effective method for cooling electronic devices. However, one must consider a tolerance limit in view of increased pressure drop to determine the optimal amplitude of external pulsation according to the porous blockage ratio and porous material.

並列關鍵字

Pulsating impinging flow ； Porous media ； Cooling enhancement

參考文獻

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