近年來科技的進步,使得運算晶片密集度越來越高,進而產生大量的熱能,因此需要一高效率的散熱系統。本研究採用高熱傳效率的方式,以池沸騰與自由噴擊方式進行電子晶片之散熱實驗,實驗中以非導電流體FC-72做為工作流體。實驗採用五個直徑0.24 mm之噴擊孔,以5 mm之距離噴擊至10 × 10 mm2之熱源面積。測試表面包含光滑表面、針狀與槽道表面,鰭片寬度尺寸範圍為0.1 mm至0.4 mm,鰭片高度由0.1至1.6 mm;其面積增加率為1至5.08。池沸騰與噴擊實驗之加熱面斜角度分為水平(0o)、45度與垂直傾角(90o);噴擊流量為30至120 ml/min。實驗結果顯示改變傾斜角度,僅在漸增熱量且低瓦數時,沸騰熱傳性能隨著傾斜角度增加而提升;但在較大熱通量且尚未達到臨界熱通量下,對沸騰熱傳性能與噴擊熱傳之影響不大。在線切割與濕蝕刻兩種表面加工方式中,因為線切割加工表面有較高的表面粗糙度與矩形鰭片根部,因此其沸騰熱傳性能較佳。 在單相與雙相之噴擊冷卻中,其熱傳性能皆隨著噴擊流量增加而提升;採用噴擊冷卻可降低起始沸騰過熱溫度,且噴擊臨界熱通量較池沸騰臨界熱通量高。不論在池沸騰或噴擊冷卻中,兩者的熱傳性能係數皆隨著鰭片高寬比增加而提升,臨界熱通量比隨著面積增加率增加而提升。經由迴歸分析而分別歸納出鰭片表面與光滑表面之沸騰與噴擊熱傳性能,以及臨界熱通量之經驗式,其誤差範圍皆在 ± 25%以內。
As chip power densities in electronic equipment increasing, improved cooling methods, including pool boiling and jet impingement using dielectric fluid, are demanded. A plain surface, four types of straight-finned surfaces, and six types of pin-finned surfaces were tested in this study to investigate the effects of fin dimensions. Fins were 0.1 ~ 0.4 mm thick and the fin lengths varied from 0.1 to 1.6 mm. Pool boiling and jet impingement experiments were conducted on 10-mm2 copper surfaces at three orientations form horizontal to vertical. The nozzle orifice had 5 pores of 0.24 mm in diameter and jet distance was 5 mm in height. The jet heat transfer coefficient was better than boiling performance at low heat flux, and removed temperature overshoot. For the plain surface, the boiling heat transfer coefficient increased as the inclination angle increased at low heat fluxes for the increasing heat flux tests. No marked effect on CHF and jet boioling heat transfer coefficient during the decreasing heat flux tests was observed for all surfaces in the present tests. The pin fins made by wire cutting yield higher boiling performance than the wet etched surfaces because of the advantage of larger surface roughness and sharper fin base corners. The heat transfer coefficient of either jet impingemnt or boiling increased with increasing fin height/width ratio or surface enhamcement ratio. The best surface was the pin-finned surface having a fin width of 0.4 mm, a fin height of 1.6 mm and a fin pitch of 0.8 mm. It enhanced the boiling heat transfer coefficient about eight fold. For the same fin height and width, the straight fins and the pin fins yield similar performance at q” < CHF (critical heat flux). However, the CHF of the pin fins was greater than that of the straight fins because the opening area on the top of the pin fins was greater than that of the straight fins. For both straight fins and pin fins, the boiling heat transfer efficiency was mainly enhanced by increasing the total surface area at q” < CHF. The CHF of jet impingement increased with increasing the jet velocity. Correlations of heat transfer coefficient of the plain and fin surfaces in boiling and jet impingement are proposed. All prediction agrees with the experimental result within ± 25 %.
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