加裝可移動的細銅線在一小水平加熱銅板上

Abstract

本論文針對加裝可饒性且具有活動力的細銅線於加熱銅塊邊緣之FC-72池沸騰飽和態的熱傳增強實驗研究。細銅線的端點固定在銅塊邊緣且線和線之間彼此互相平行。在實驗中探討尼龍線線徑、尼龍線固定端點和加熱面的距離、尼龍線的長度藉以控制鬆弛程度以及部分線和線之間間距的效應。在實驗參數範圍上，熱通量q從0.1到7 W/cm2，尼龍線直徑從79到254 μm，細銅線和加熱面的距離從0到2 mm，線的長度由10 到12 mm以及線和線之間間距1 mm。 實驗數據以壁過熱度對應輸入的熱通量及熱傳係數表示，比較對於光滑加熱銅塊下熱傳增強的表現。施加細銅線相較於光滑表面對於FC-72之池沸騰熱傳係數有65%的增強效果。由數據呈現的圖形可得，熱傳增強的表現會因其不同的參數搭配而有不同的增強效果，理想且良好的熱傳增強表現在於適當的線徑、長度和固定端點的高度搭配。 可視化的氣泡流過銅板的結果指出，在光滑表面安裝細銅線後在某些例子中氣泡數量有明顯地增加。此外，流動中有較大的氣泡。

An experiment is carried out here to investigate how the saturated pool boiling heat transfer of liquid FC-72 over a small horizontal heated copper plate ( ) is affected by placing flexible and movable fine copper strings above the plate surface, intending to explore the possible pool boiling heat transfer enhancement by the strings. The strings of uniform size are fixed only at their ends and are parallel with each other. In the experiment, the imposed heat flux is varied from 0.1 to 7 W/cm2, the diameter of strings from 79 to 254μm, the string-heated surface separation from 0 to 2 mm, and the length of the strings from 10 to 12 mm for the pitch of the strings fixed at 1 mm. The measured data are presented in terms of the boiling curves and boiling heat transfer coefficients for the heating surface with and without the installation of the strings. Effects of the experimental parameters on the possible boiling heat transfer enhancement are examined in detail. The data obtained from the present study for the saturated pool boiling indicate that placing the copper strings can increase the pool boiling heat transfer coefficient of FC-72 more than 65% over that for a bare surface for a certain combination of the experimental parameters. However, the boiling heat transfer enhancement varies nonmonotonically with the string size, length and height, reflecting the complex influences of the strings on the bubble motion near the heated surface. An optimal boiling heat transfer enhancement could be procured by a suitable choice of the experimental parameters. The results from the visualization of the boiling flow over the copper plate indicate that installing the copper strings above the plate surface can significantly increase the bubble population in the flow for some cases. Besides, more big bubbles appear in the flow.