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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/68502


    Title: 梯形流道表面之池沸騰熱傳性能研究;Pool boiling on open trapezoidal channel surface
    Authors: 蘇邁亞;Subrahmanya,Praveena Alangar
    Contributors: 能源工程研究所
    Keywords: 流道表面;表面粗糙度;沸騰熱傳增強;碰撞流動;汽泡流動;臨界熱通量;Channel surface;roughness;heat transfer enhancement;bubble dynamics;CHF
    Date: 2015-08-05
    Issue Date: 2015-09-23 11:57:27 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 本研究使用壓力為一大氣壓下的甲醇為工作流體,並以開放梯型流道為池沸騰熱傳表面進行池沸騰熱傳實驗。沸騰表面流道之參數有深度與鰭片間距兩種。深度分別為0.1mm、0.3mm、 0.6mm與0.9mm,且各深度另有三種不同的鰭片間距。沸騰表面之流道皆使用放電加工製作。並與平滑板之實驗結果做比較。本研究使用兩種不同方法製作平滑板,一種使用砂紙研磨表面,另一種則使用放電加工製作。
    藉由量測可知,使用放電加工製作的平滑板表面粗度大於使用砂紙研磨之平滑板。而由實驗結果可得,在不同熱通量下,以放電加工製作之平滑板為沸騰表面皆有較佳之熱傳性能。在所有沸騰表面中,因流道表面之粗糙度較大,成核孔洞相對較多,因此汽泡皆由流道表面產生。若流道深度增加,藉由汽泡之觀察可發現兩種獨特的氣泡流動方式明顯改變了熱傳機制。以流道深度為0.1mm為沸騰表面時,流道只產生單一汽泡,因此熱傳性能與流道數成直接正比之關係。以0.3mm到0.9mm之深度為沸騰表面時,成核孔洞則隨深度增加而增多。若降低鰭片間距並增加流道深度,成核孔洞數目相對增加。因此,增加沸騰表面積為一提高熱傳性能之重要參數。另外,若增加流道深度,流道所產生之汽泡體積較大,使的液體補充回流道時流速較快,有助於單相流體之對流流動。因此,將液、汽之流動路徑分離,有助於延後臨界熱通量的發生。

    關鍵字: 流道表面,表面粗糙度,沸騰熱傳增強,碰撞流動,汽泡流動,臨界熱通量
    ;In this thesis pool boiling experiment is carried out on open trapezoidal channel surface to study the effect of channel top width (0.4mm, 0.8mm, 1.4mm and 2.0mm) and fin pitch using saturated methanol as working fluid at one atmospheric pressure along with bubble dynamic visualisation. The channel were cut using wire electro-discharge machining technique and results are compared with corresponding plane surfaces.
    Plain boiling surface with comparatively high roughness value (manufactured by wire electro-discharge machining) consistently showed higher heat transfer performance than emery surface with lower roughness value. All channel surfaces performed better than plain surface prepared by emery paper. For all the tested trapezoidal channel surfaces, bubbles only generated from the channel surface because of high roughness on channel surface. There was no bubble generation from fin top surface. Therefore overall channel surface area played major role along with the effect of channel geometry on HTC & CHF and the results are meant to compare with plain surface made by EDM process.
    Two distinctive bubble dynamics are observed as the channel top width increased. For channel having top width 0.4mm, single bubble generated across the channel and it attached to channel side surface and grew on top of channel till the departure. Therefore the heat transfer performance increased as the fin pitch reduced. But in comparison with Plain EDM surface, its nucleate boiling HTC found to be lower because overall available boiling surface area (ie channel surface area) is lower.
    From channel having top width 0.8mm to 2.0mm, number of nucleation sites across channel surface increased accordingly with the channel cross section area. Therefore multiple bubble nucleation sites were observed. On these channel top width surfaces, a heat transfer enhancement mechanism observed. Therefore even though the channel surface area was lower than that of plain EDM surface, nucleate boiling HTC were either equal or more than plain EDM surface observed. Reduction in fin pitch had no major effect on HTC.
    For channel made by EDM process having different roughness value in comparison with fin top surface has different liquid and vapor flow path ways. Majority of the liquid supply to rewet the boiling surface (i.e channel surface) were from fin top surface. As the fin pitch decreases, CHF found to increase for all tested channel top widths because of increases in channel surface area as well as enhancement in heat transfer mechanism over channel surface.
    Appears in Collections:[能源工程研究所 ] 博碩士論文

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