加裝可移動的尼龍線在一小水平加熱銅板上對FC-72池沸騰熱傳增強及氣泡特性研究

Abstract

本論文針對加裝可饒性且具有活動力的尼龍線於加熱銅塊邊緣之FC-72池沸騰飽和態和次冷態的熱傳增強實驗研究。尼龍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74到259 μm，尼龍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和2 mm，工作流體次冷度從0□C到10□C。 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，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，並且在次冷態的熱傳增強方面和飽和態有近似的趨勢。

An experiment is carried out here to investigate how the saturated and subcooled pool boiling of liquid FC-72 over a small horizontal heated copper surface is affected by placing flexible and movable nylon strings above the 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 74 to 259μm, 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 mainly fixed at 2 mm. Besides, the subcooling in the bulk FC-72 liquid is chosen to be at 5□C and 10□C. The measured data are presented in terms of boiling curves and the boiling heat transfer coefficient at the heating surface with the installation of the strings and for a bare surface. 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 and subcooled pool boiling indicate that placing the flexible and movable nylon strings can increase the pool boiling heat transfer coefficient of FC-72 more than 100% 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 complicate influence of the strings on the bubble motion near the heated surface. An optimal boiling heat transfer enhancement can be procured by a suitable choice of the experimental parameters. Besides, the effects of the experimental parameters on the boiling heat transfer enhancement are similar at different subcoolings of FC-72.