介電液FC-72於小間隙雙套管內冷凝熱流特性之研究

Abstract

本論文主要以實驗的方法分析介電液FC-72在外徑25mm及內徑22mm的水平雙套管中之冷凝熱傳係數與壓降，並分析流譜。實驗結果發現冷凝熱傳係數隨著質通量、乾度上升而增加。在中高乾度時，質通量對於冷凝熱傳係數的影響會更明顯。冷凝熱傳係數是隨著熱通量提高而上升，但是在質通量為 時卻有不同的現象，當熱通量由 提高到 時，因為低質通量加上冷凝液膜的關係，反而使得熱傳係數有下降的趨勢。至於壓降部分，質通量對於壓降的影響則和冷凝熱傳係數相同，但熱通量對於壓降並沒有相當明顯的影響。目前通用的Akers和Shah凝結熱傳關係式都不能做出準確的預測，所以修改Akers的關係式獲得一新經驗式，以應用於此類冷凝器的設計。

This thesis experimentally investigated the condensation transfer coefficient and pressure drop characteristics of dielectric liquid FC-72 in a horizontal annulus,as well as the flow patterns. The horizontal annulus has 22mm I.D. and 25 O.D.The heat transfer coefficients were shown to rise with the mass flux and mean vapor quality.Mass flux has a greater effect on heat transfer coefficient at mean and higher quality. Generally, heat transfer coefficients increased with higher heat flux,but the results showed that at mass flux G=75kg/㎡s the condensation heat transfer coefficients were lower for lower mass flux during heat flux from 2.5kW/m^2 to 5kW/m^2.As for the pressure drop,mass flux and vapor quality have the same effect on pressure drop, but the heat flux has small effect on pressure drop. The Akers and Shah correlations did not predict well in this study.For practical design of condensers a new empirical correlation was proposed.