R-410A冷媒於水平雙套管中次冷及飽和流動沸騰與蒸發熱傳及氣泡特性之實驗研究

Abstract

在這篇論文中對於R-410A冷媒於水平雙套管中過冷、飽和流動沸騰與蒸發熱傳之實驗作了詳細的研究，此外，水平雙套管中流動沸騰相關的氣泡特性，也藉由流場觀測的方式去瞭解。實驗參數的範圍，冷媒流量G從100到200 kg/m2s，測試段熱通量q從0到30 kW/m2，入口過冷度DTsub為0到7 ℃，系統壓力設定在1.25，1.36和1.44 Mpa (Tsat =15℃, 18℃ and 20℃)。 我們藉由沸騰曲線圖、熱傳係數的方式來呈現次冷沸騰的實驗結果，沸騰曲線圖中顯示次冷沸騰的磁滯現象很明顯，所有的流量、過冷度和飽和溫度等實驗參數範圍中，皆有不小的磁滯現象發生。而在過冷度影響熱傳係數的方面，特別的是，高過冷度會產生較低的熱傳係數。再者，氣泡的成長稍微受到了高流量及過冷度的抑制，氣泡脫離半徑和產生率，深受測試段熱通量和入口過冷度的影響。 R-410A的飽和流動沸騰實驗中磁滯現象很難被偵測到，熱傳係數主要受到測試段熱通量的影響，而冷媒流量影響則不大，增加冷媒流量會使平均的氣泡脫離半徑減小；在較高的熱通量下氣泡的成長顯著的變快。另外，飽和流動沸騰中平均的氣泡脫離半徑，稍微比次冷流動沸騰還大。 在水平雙套管中R-410A的蒸發實驗研究中，熱傳係數隨平均乾度、熱通量和冷媒流量的增加而明顯增加，然而冷媒飽和溫度對於熱傳係數的影響則幾乎可以忽略。 最後，我們把這個實驗中沸騰與蒸發熱傳係數以及氣泡脫離半徑和產生率的資料作分析，求出經驗公式。

The subcooled and saturated flow boiling and evaporation heat transfer of R-410A in a horizontal annular duct are investigated experimentally in this study. Besides, the associated bubble characteristics in the horizontal annular duct are also inspected from the flow visualization. Experiments are carried out for the mass flux G varied from 100 to 200 kg/m2s, imposed heat flux q from 0 to 30 kW/m2 and liquid inlet subcooling DTsub from 0℃ to 7℃ for the system pressure set at 1.25 MPa, 1.36 MPa and 1.44 Mpa (Tsat =15℃, 18℃ and 20℃). The results for the subcooled flow boiling are presented in terms of the boiling curves and heat transfer coefficient. The boiling curves show that the hysteresis in the subcooled boiling is rather significant over the entire ranges of the refrigerant mass flux, inlet subcooling and saturation temperature tested here. Besides, the subcooled boiling heat transfer coefficient is significantly affected by the inlet subcooling of the refrigerant. More specifically, at a higher inlet subcooling the boiling heat transfer coefficient is lower. Moreover, bubble growth is somewhat suppressed by the higher refrigerant mass flux and inlet subcooling. The bubble departure diameter and generation frequency is substantially influenced by the imposed heat flux and inlet subcooling. In the saturated flow boiling of R-4110A no boiling hysteresis is detected in the experiment. The boiling heat transfer coefficient is mainly affected by the imposed heat flux and the refrigerant mass flux shows much smaller effects. Increasing refrigerant mass flux decreases the mean bubble departure diameter. Bubble growth is substantially faster for a higher imposed heat flux. The mean bubble departure diameter for the saturated flow boiling is somewhat larger than that for the subcooled flow boiling. In the evaporation of R-410A in the annular duct, the heat transfer coefficient increases significantly with the mean vapor quality, imposed heat flux and refrigerant mass flux. However, the saturation temperature of the refrigerant shows negligible effects on the heat transfer coefficient. Finally, correlation equations are proposed to fit the data from the present study for the boiling and evaporation heat transfer coefficients along with the bubble departure diameter and generation frequency.