介電液FC-87對水平加熱線池核沸騰熱傳分析

Abstract

本研究計劃主要是探討介電液FC-87之池核沸騰現象。分別以三種不同線徑的鎢絲與鉬絲，水平裝置於池沸騰測試容器中，以控制電壓及電流的方式加熱，進行池核沸騰實驗，以瞭解這種高潤濕度、低表面張力的介電液在成核過程中的現象及其池核沸騰熱傳特性。實驗結果顯示：對於線徑較小的加熱線，熱傳係數較高，線徑0.1mm的鎢絲熱傳係數約為線徑0.3mm鎢絲的1.1~1.25倍，鉬絲則為1.2~1.4倍，而比較同線徑的鎢絲與鉬絲，以鎢絲的熱傳係數較高。在起始沸騰時有17.8至32.2℃的起始過熱度，且造成5至14℃的溫度偏離。六組實驗在熱通量1.7 105W/m2至2.35 105W/m2即到達臨界熱通量，線徑較小會有較高的臨界熱通量。對介電液FC-87而言，可利用Danielson修正的Rohsenow關係式預測加熱線沸騰熱傳係數，實驗值誤差在30%範圍內。對於臨界熱通量，可用You提出的關係式來預測，但有高估的趨勢。

The performance of nucleate pool boiling of dielectric liquid FC-87 on horizontal wires were investigated in this study. In order to understand the pool boiling heat transfer characteristics for high wetting low surface tension dielectric liquid, the liquid were boiled using 0.1-, 0.2- and 0.3-mm-diameter wires made of tungsten and molybdenum. The experimental results show that boiling heat transfer coefficients decreased withincreasing wire size. Compared tungsten and molybdenum of the same diameter, tungsten has higher heat transfer coefficients. The data showed incipience superheat of 17.8~32.2℃ and temperature excursion of 5~14℃. CHF occurs at heat flux between 1.7 105W/m2 and 2.35 105W/m2 ,and the smaller diameter wire has higher CHF .The Rohsenow correlation corrected by Danielson can predict experimental data of nucleate boiling heat transfer coefficients within 30% band of uncertainty. We can use You correlation to predict CHF , and prediction values are higher than experimental data.