液體微熱交換器之熱傳增強研究

A study of Enhanced Heat Tansfer in Micro Heat Exchanger for Liquid Cooling

葉竣達(Chun-ta Yeh)

指導教授 ： 楊建裕

國立中央大學/工學院/機械工程學系/博士(2008年)

摘要

本文以熱傳增強設計並製作出長寬50 mm x 50mm，厚度2 mm之微熱交換器，包括：山型紋微熱交換器、長斷續式鰭片微熱交換器、短斷續式鰭片微熱交換器，與直線流道微熱交換器相比較；並將斷續式鰭片加以流線化之翼形與梭形斷續式鰭片，與矩形斷續式鰭片比較，測試分析微熱交換器的性能。
斷續式鰭片與山型紋的熱增強設計皆可有效降低微熱交換器的熱阻，短斷續鰭片微熱交換器之熱阻稍低於長斷續鰭片微熱交換器，而以山型紋微熱交換器中心溫度與熱阻最低，增強效果最明顯。但是如果以所需的泵動力來看，山型紋微熱交換器所需泵動力最高。斷續式鰭片微熱交換器也有不錯的熱傳增強效果，但相對壓降較小。
流線型斷續鰭片長度同為3.0 mm時，翼形鰭片摩擦係數較矩形斷續鰭片降低20 %，紐賽數只降低10%以內。鰭片長度1.0 mm之翼形鰭片微熱交換器在相同泵動力下熱阻最低，鰭片長度0.6 mm之翼形鰭片微熱交換器因為鰭片頂端過度側蝕，熱傳性能因此下降。
梭形鰭片微熱交換器有兩個不同的排列方式，其一與矩形和翼形的鰭片排列方式同為平行錯置之斷續式排列，另一種則將錯置部分重疊使鰭片在熱交換器表面上更為密集。錯置部分重疊使中心溫度約降低2.8 oC，熱阻降低約13 %。原因在於提前錯置的斷續排列鰭片流道變窄後，相同流量下局部流速上升而提高熱傳係數，但壓降較原本的斷續排列增加46%。部分重疊斷續排列之梭形鰭片微熱交換器可藉流道縮小與鰭片數增加降低熱阻，但相對壓降增加較多。

關鍵字

熱傳增強 ； 山型紋 ； 翼形 ； 梭形 ； 水冷 ； 微熱交換器

並列摘要

Three micro heat exchangers for use in a liquid cooling system with a long offset strip, short offset strip, and chevron flow path based on the tra-ditional heat transfer enhancement concepts were designed and tested. A straight channel heat exchanger was also made for comparison. This study also follows the offset strip flow path design, replaces rectangle strips by airfoil and shuttle type strips to reduce its flow resistance.
The test results show that the chevron channel heat exchanger pro-vides the lowest thermal resistance. However, its pressure drop is also the highest, approximately five times higher than that for other three heat ex-changers. The offset strip heat exchangers provide better thermal perform-ance than does the straight channel heat exchanger. The performance of the heat exchanger with the shorter strip is better than that of heat exchanger with longer strip.
The effects of strip length, strip type and strip arrangement were con-sidered for heat transfer performance comparison. The test results show that the heat exchangers with shorter strip length and narrower strip space provide better heat transfer performance.
The short airfoil strips heat exchanger with 1.0 mm strip length per-formed the lowest thermal resistance among all types of heat exchangers. Because of its narrow flow paths, the performance of the overlapped shuttle strip heat exchanger is better than that of the offset shuttle, long airfoil, and rectangle strip heat exchangers. However, the space between strips is lim-ited by the fabrication techniques and is difficult to be made narrower by the method of chemical etching.

並列關鍵字

micro heat exchangers ； liquid cooling ； heat transfer enhancement ； chevron ； airfoil ； shuttle

參考文獻

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