一種應用於增強自然對流之新型散熱片開發研究

Abstract

This thesis performs a comparative study of heat sinks having various profiles. The present study examines the contribution from both natural convection and radiation heat transfer pertaining to various fin arrays on a horizontal base plate. The investigation is performed both numerically and experimentally. The fin geometry includes Rectangular, Trapezoidal, inverted Trapezoidal (so-called dovetail fin), rectangular notched, trapezoid fins with and without staggered fin arrangement. The main purpose of this research is to examine the associated heat transfer performance of these fin layouts. Tests were conducted in an environmental chamber and a vacuum chamber from which the contributions by natural convection or radiation can be discriminated. Yet the heat transfer rate spans from 3W, 5W, 10W, 15W, 20 W and 25W. The effective heat transfer coefficients are determined for the various heat sinks having the same base, fin pitch and total area. Based on the test results and analysis the rectangular notched fins (115 degrees) yields the highest average heat transfer coefficient due to the notched which can entrain more air flow through the cutting notch. In addition, although the cutting notch may impair heat conduction from the base, the resultant higher temperature difference of the base and fin tip may mimic a “chimney effect” and introduce more air flow into the heat sink. Accordingly, a better heat transfer performance is encountered. From the experiments, Nu was determined as a function of Ra at Pr=0.7 for an orientation with Ran ranging between (43470 and 319200). The thermal resistance of the rectangular notched fins was 23.22% less than the inverted trapezoidal fins which is desirable.

本文對具有各種型材散熱器的比較研究。本研究利用模擬及實驗觀察來自自然對流和有關各鰭片陣列上水平底板輻射傳熱的貢獻。鰭片幾何包括矩形，梯形，倒梯形，矩形缺口，梯形鰭片有和沒有交錯的鰭片佈置。這項研究的主要目的是檢查這些鰭片佈局的相關熱傳性能。實驗將鰭片放置於自然對流恆溫箱和真空箱中，分別觀察其自然對流和輻射的貢獻。在加熱源3 W、5 W、10 W、15 W、20 W和25 W的條件下，測試不同間距及面積的散熱片。根據測試結果，矩形缺口鰭片（115 度）產生最高的平均熱傳係數，因為空氣可以由缺口進入，提升其熱傳性能。此外，雖然在切割缺口，可能會降低鰭片基座的熱傳導性能，但基座和鰭片尖端的較大的溫度差可以產生“煙囪效應”，並引入更多的空氣流入散熱片，達到更好的熱傳性能。實驗中，在Pr = 0.7 的情況下，由Ra(43470 ~ 319200)來決定Nu的大小。希望矩形缺口鰭片的熱阻可以達到比倒梯形鰭片減少23.22％。