冷媒R-134a對水平圓管的池核沸騰加強熱傳分析

Abstract

本研究論文主要是探討冷媒 R-134a的池核沸騰加強熱傳方法。在池沸騰的測試容器中，分別以平滑管、16fpi微鰭管、覆網鰭片管及表面噴砂粗糙等四種不同表面的圓管，以控制電壓及電流的方式對工作流體R-134a加熱，在不同飽和壓力下進行水平加熱池核沸騰實驗，以了解不同結構的熱傳加強表面（enhancement surface）對池核沸騰熱傳性質的影響，進而找出較佳的熱傳加強表面結構以及影響池核沸騰熱傳表現的參數。本論文亦發展以減縮壓力及熱通量為主要參數的沸騰熱傳關係式。實驗結果顯示：覆網鰭片管有最佳的沸騰熱傳關係，其次為表面噴砂粗糙管及16fpi微鰭管，三者比平滑管熱傳係數各增強了2.3、1.7及1.3倍。平滑管的實驗熱傳係數由Cooper熱傳關係式可預測90%的值於誤差20%內；由Stephan and Abdelsalam熱傳關係式可預測85%的值於誤差±20%內。而本文中所發展的熱傳加強管的池沸騰關係式預測頗為精準，能涵蓋85%的實驗數據在誤差±20%之內。

The method of enhanced nucleate pool boiling of refrigerant R-134a on horizontal circular tubes were investigated in this study. In order to understand the pool boiling heat transfer characteristics for different enhancement surfaces and the related parameters of the pool boiling heat transfer, the experiments were conducted using an plain tube, and three enhanced tubes including a integral fin tube, a mesh 50 tube and rough tube with the applications of decreasing heat flux at defferent saturated pressures. The developments of heat transfer correlations of nucleate boiling in terms of reduced pressure and heat flux are presented. The experimental results show that the mesh50 tubs has the highest hest transfer coefficients and that the rough tube and the 16fpi tube have the next highest values. The augmentation of the heat transfer coefficients of the mesh50 tube, the rough tube and the 16fpi reaches 2.3, 1.7 and 1.3 times respectively compared to that of the plain tube. The Cooper correlation can predict 90% of the experimental data of the plain tube within 20% hand of uncertainty. The Stephan and Abdelsalam correlation can predict 85% of the experimental data of the plain tube within35% band of uncertainty. The correlations developed in this study can predicted the experimental heat transfer coefficients of the three enhanced tubes with good accuracy to predict 85% of the experimental data within 20% band of uncertainty.