Experimental Study of Flow Boiling and Evaporation Heat Transfer of R-410A and Bubble Characteristics in Horizontal Annular Duct
|Keywords:||R-410A;流動沸騰;蒸發熱傳;氣泡特性;水平雙套管;R-410A;flow boiling;evaporation heat tansfer;bubble characteristics;horizontal annular duct|
|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℃)。
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.
|Appears in Collections:||Thesis|