介電液FC-72於小間隙雙套管內蒸發熱流特性之實驗研究

Abstract

本論文以實驗方法探討介電液FC-72於小間隙雙套管內，飽和壓力1.15大氣壓的蒸發熱傳係數與兩相流動壓降特性，並觀察其流動情形以研究兩相蒸發的熱傳機制。測試段為內徑22mm、外徑25mm，間隙1.5mm的水平雙套管，質通量範圍為 ，熱通量範圍為 。結果顯示熱傳係數及壓降均隨乾度、質通量及熱通量的增加而增加。但質通量對於壓降在高乾度區才有顯著的影響，而熱通量影響的效果非常有限。將本實驗熱傳係數及壓降的實驗值與前人之熱傳經驗式及壓降經驗式做比較，發現熱傳經驗式的預測值以Wattelet&Chato(1994)最佳，在±40％以內；而Friedel(1979)及Souza(1993)的經驗式對於液態摩擦乘數的預測均低估了本實驗的實驗值。在質通量 ，熱通量 ，由不同乾度的流譜可視化照片可看出當乾度為0.09時，流譜的型態趨近為柱塞流（Plug Flow），當乾度為0.399時，此時的型態趨近於為波浪流（Wavy Flow）或塊狀流（Slug Flow），當乾度增加至0.65時，液膜幾乎已乾化，僅剩下底部的小部分液體。

The characteristics of evaporative heat transfer coefficient and two-phase flow pressure drop for FC-72 at saturation pressure 1.15atm in a small-gap annulus were investigated experimentally and observed by flow pattern observation. The test section was a horizontal annulus with inside diameter 22mm, outside diameter 25mm with a gap 1.5mm. The range of mass flux was from 50 to 100 and heat flux from 1.0 to 5.0 . The results showed that the heat transfer coefficients and pressure drops both increased with quality, mass flux and heat flux. For pressure drops, the effect of mass flux was noticeable at high vapor quality, but the effect of heat flux was much smaller than that of mass flux. When compared with experimental data for proposed correlations reported in the literature, Wattelet&Chato’s(1994) heat transfer correlation predicted well within ±40%, but Friedel’s(1979) and Souza’s(1993) pressure drop correlation predicted very poorly. For mass flux of , heat flux of and quality of 0.09, the flow pattern was plug flow. For quality of 0.399, the flow pattern was wavy flow or slug flow. For quality of 0.65, the liquid film almost dried out and just had few liquid at the bottom portion of the annulus.