衝擊冷卻於多孔性流道之熱傳研究

Abstract

本實驗為將多孔性材質擺入衝擊冷卻的衝擊側，並分析其對衝擊冷卻的影響。配合暫態液晶量測技術，分析衝擊面的熱傳情形。 本衝擊實驗為使流體流經一個具有4×12個圓形孔洞陣列之孔口板，產生正向衝擊面的噴流，並以此進行熱交換。孔口板上每個孔洞的直徑皆為0.5cm，各孔洞的間距與孔洞直徑的比值為4，而孔口板至衝擊面的距離與孔洞直徑之比值為3，我們改變雷諾數2500、5100與7700，並且將多孔性材質依塞滿率分為全塞滿、半塞滿與1/4塞滿，比較在不同情況下多孔性材質對衝擊冷卻的影響。結果顯示，多孔性材質於衝擊冷卻中，會阻礙噴流接觸到衝擊面，使得直接對衝擊面的熱傳減少，而隨塞滿率提高或者距離孔口板越遠，其阻礙效果越明顯。而當多孔性材質部分覆蓋孔口板時，不利氣流流經孔口板，反而可能造成沒多孔性材質處的熱傳稍為提升。而比較整體紐賽數平均，多孔性材質塞滿率為1/4的情形其熱傳較高，與無多孔性材質時大約下降13%，而全塞滿的情形最糟，平均紐賽數僅無多孔性材質之50%左右。

Jet Impingement Cooling with porous medium was experimentally investigated using transient liquid crystal technique. In this experiment, porous medium was put inside the impingement channel. This jet impingement experiment was conducted using an orifice plate with 4×12 circular holes . The diameter of the hole is 0.5cm, and the jet-to-jet distance is 4 times the hole diameter. With the target-to-orifice distance of 3 times the hole diameter, we investigated the jet Reynolds numbers of 2500, 5100 to 7700. We proposed and compared some test condition when the porous medium in the impingement channel. For example, the fill ratios of the porous medium are 1, 1/2 and 1/4. The experiment result shows that the porous medium in the impingement channel would make the jet flow dispersed and decrease the direct impingement of the jet flow on the target surface. And the heat transfer coefficient decrease more obviously when the fill ratio of the porous medium is increased or the porous media is located away from the orifice plate. When the porous medium partially covers the orifice plate, the air flow through the porous medium is hindered and the heat transfer coefficient is enhanced for the region without porous medium little. The higher heat transfer is found when the fill ratio of the porous medium is 1/4, but the total average Nusselt number is still 13% lower than the case without porous medium. The heat transfer with the fill ratio of 1 is the worst, and the total average Nusselt number is only 50% compared to the case without porous medium.