介電液FC-72在微小管道內的蒸發與熱流分析

Abstract

本論文以實驗方法探討介電液FC-72於水平微小管道內，飽和壓力在1.3大氣壓時之蒸發熱傳係數與兩相流動壓降特性，並藉由拍攝流譜的方式來探討兩相蒸發的熱傳機制。測試段包含內徑為4.35㎜及3.17㎜之水平光滑圓管，實驗的測試範圍為質通量 ，熱通量為 。結果顯示內徑為3.17㎜的平滑管在質通量 時，熱傳係數高於4.35㎜管；而在 的低乾度區域時，內徑為3.17㎜的平滑管的熱傳係數高於4.35㎜管，高乾度區域則因為3.17㎜平滑管內乾涸的現象較嚴重反而導致熱傳係數低於4.35㎜；在 時，內徑為3.17㎜的平滑管的熱傳係數均低於4.35㎜管。 壓降均隨著乾度、熱通量、質通量的增加而增加，而摩擦壓降亦隨著管徑的縮小而增加。經由流譜的可視化得知，在乾度為0.1時，三種質通量流譜的型態為波浪-塊狀流(Wavy-Slug Flow)，而隨著乾度的增加，流譜的型態均轉換為環狀流(Annular Flow)。而在乾度為0.7時，可看出流譜均有乾化的現象，幾乎僅剩一層液膜。 本論文並發展了一個修正的兩相熱傳關係式：

This thesis experimentally investigated the evaporative heat transfer coefficient and pressure drop characteristics of dielectric liquid FC-72 at 1.3 atm in horizontal small-diameter circular tubes, as well as the flow patterns. The test sections are two smooth tubes, with 3.17mm and 4.35mm inner diameter respectively. Experiments were carried out for mass flux from 250 to 400 , and imposed heat flux from 2.5 to 10 . The results showed that at mass flux , the heat transfer coefficient of tube 3.17mm was higher than that of tube 4.35mm. At mass flux , in the low quality region, the heat transfer coefficient of the tube 3.17mm was also higher than that of tube 4.35mm. But in the high quality region, the heat transfer coefficient of tube 3.17mm was lower than that of tube 4.35mm because of the dryout of tube 3.17mm. At mass flux , heat transfer coefficient of tube 3.17mm was lower than tube 4.35mm. Pressure drop was shown to rise by the higher quality, mass flux and heat flux. Frictional pressure drop was also increased by the decreasing of the test section inner diameter. At low quality of 0.1, the flow pattern was wavy-slug flow. By increasing of the quality, the flow pattern changed into annular flow. And at quality of 0.7, the flow pattern was shown to approach dryout. This thesis also developed a correlation of the two-phase heat transfer coefficient as: