介電液FC-72 在垂直矩形流道之流動沸騰實驗研究

Abstract

本論文以實驗方法探討介電液FC-72 於垂直矩形流道內之流動沸騰現象。在完全發展流的狀態下，流經表面積為10mm*10mm 平滑表面之加熱銅塊，進行沸騰熱傳分析。本實驗矩形流道剖切面之高度為3mm、寬度為12mm、水力直徑為4. 8mm。本實驗之操作條件為介電液FC-72 在一大氣壓下、雷諾數為800、1600、2400，次冷度為33℃、28℃、23℃。本流動沸騰實驗結果皆會發生沸騰曲線之遲滯現象。在單相熱傳區及部份發展核沸騰區，隨次冷度及流速之增加對加熱壁面溫度的影響會逐漸減低，而所有不同次冷度及流速之沸騰曲線在接近核沸騰起始點會幾乎重疊；當達到完全發展核沸騰時，次冷度及流速之影響會逐漸減小；而臨界熱通量及熱傳係數則隨次冷度與流速的增加而升高，但熱傳係數在接近臨界熱通量時會稍有減小的趨勢。

The goal of this thesis is to investigate the flow boiling phenomena of di-electric liquid FC-72 in a vertical Rectangular channel by experimental method. At a state of fully developed flow, the boiling heat transfer of the FC-72 flow through a smooth heated copper block which surface area of 10mm square is analyzed. The experimental test section is a rectangular channel with a cross section of height of 3 mm, width of 12 mm, the hydrodynamic diameter of 4.8 mm. The operation conditions of FC-72 in the experiment are 1 atm， fluid Reynolds number 800，1600，2400, and subcooled temperatures of 23℃，28℃，33℃ . The results of the flow boiling experiment show that hysteresis of boiling curve always exists. At the region of single phase heat transfer and partially developed nucleate boiling，increasing both subcooled temperature and fluid velocity would reduce the wall temperature gradually. All boiling curves of different subcooled temperature and Reynolds number almost coincide near the onset of nucleate boiling.In the region of fully developed nucleate boiling，the influences of both Reynolds number and fluid subcooled temperature are reduced gradually. Besides，both the critical heat flux and the heat transfer coefficient increase with increasing fluid subcooled temperature and Reynolds number，but the heat transfer coefficient would decline severely in the vicinity near the critical heat flux.