Enhancing Evaporative Heat Transfer Using Si Micropillar Array/Microcavities
|關鍵字:||熱管;蒸發;沸騰;毛細結構;Heat pipes;evaporation;boiling;wick structure|
|摘要:||本研究提出一嶄新的嵌入微孔洞之矽微米線陣列之熱管蒸發段之毛細結構。此結構以微孔洞陣列在低過熱度時觸發沸騰以增強毛細結構之熱傳係數，同時此微孔洞陣列並不會影響矽微米線陣列之毛細力，故此嵌入微孔洞之矽微米線陣列可以提高毛細結構之熱傳係數並同時維持高的毛細限。實驗結果顯示以去離子水為工作流體，在一大氣壓與100 ℃時，在高度170 μm之矽微米線陣列含寬度40 μm、深度40 μm之微孔洞之毛細結構內所得之熱傳係數可達6.43 W/cm^2-K，與高度為170 μm之全微米線陣列相比，其熱傳係數最多可提升約66 %，同時其乾涸熱通量最高可維持在100 W/cm^2以上。此外，微孔洞可在低過熱度時即觸發沸騰，並且由實驗發現深度大於100 μm之微孔洞較易誘發沸騰。|
A novel wick structure for the application in the evaporator section of heat pipes/vapor chambers is synthesized. The wick structure consists of a micropillar array embedded with microcavities. The microcavities in the wick structure can enhance heat transfer by triggering boiling at low wall superheat. At the same time, the micropillar array could provide a high dry-out heat flux. As a consequence, the heat transfer coefficient and dry-out heat flux of heat pipes/vapor chambers could be simultaneously enhanced using the proposed wick structure. In this work, evaporation of saturated de-ionized water on micropillar array embedded with different sizes of cavities is studied. Experimental results show that the wick structure with a 170 μm high micropillar array embedded with cavities having width and depth of 40 μm has a heat transfer coefficient of 6.43 W/cm^2-K, which is 66 % higher than that of a wick structure consisting of only the micropillar array. Meanwhile, the dry-out heat flux of approximately 100 W/cm^2 can be achieved on the wick structure. It is also found that the microcavities in the wick structure could trigger boiling at a low wall superheat and the wicks with cavities deeper than 100 μm could trigger boiling more frequently than the wick with shallow cavities.