介電液FC-72在微小管道的冷凝熱流分析

Abstract

本文主要以實驗的方法分析凝結熱傳及壓降在小管徑流道的情形，以FC-72為工作流體在內徑3.17mm及2.5mm的平滑管內測量凝結熱傳係數與壓降並分析流譜，以期分析影響凝結熱傳與壓降的參數和機制。實驗結果發現熱傳係數隨著質量速度與乾度的增加而增加，隨管徑的縮小而略微上升，而熱傳係數大致是隨熱通量的上升而變大，但是在質量流速為500kg/㎡s時卻有不同的現象；壓降則隨質量速度的上升、管徑縮小及乾度變大而增加，隨熱通量的縮小而略微增加；而在高乾度時質量速度對熱傳係數以及壓降的影響會更明顯。目前通用的各個凝結熱傳關係式都不適用於FC-72於微小管道的凝結熱傳現象。至於在凝結熱交換器的設計上，外加的凝結熱通量需要配合適當的質量速度與測試管材質及尺寸，才能夠達到工作需求。

This thesis experimentally investigated the condensation heat transfer coefficient and pressure drop characteristics of dielectric liquid FC-72 in horizontal small-diameter circular tubes, as well as the flow patterns. The test sections are two smooth tubes, with 2.5mm and 3.17mm inner diameter respectively. The heat transfer coefficient was shown to rise by the higher quality, mass flux and heat flux. But the results showed that at mass flux G=500kg/㎡s was different. Pressure drop is also the same with the heat transfer coefficient. The most of the different factors is the tube inner diameter. This factor is more powerful in the pressure drop than in the heat transfer coefficient.The correlations of the two-phase condensation heat transfer coefficient were not suitable for small tube.