新式環保冷媒R-1234ze與R-134a於外徑9.52mm微鰭管與平滑管內之沸騰對流熱傳與壓降分析與比較

Abstract

本研究以實驗方法探討冷媒R-134a及R-1234ze於外徑9.52mm微鰭管與平滑管內的兩相流動壓降、對流沸騰熱傳係數。質量速度範圍為60-200kg/m2s，熱通量為5-15kW/m2，飽和溫度為10℃-20℃。實驗結果顯示，R-134a與R-1234ze的熱傳係數均會隨著質量速度、熱通量、乾度與飽和溫度的上升而提升。在低乾度時，熱通量效應對熱傳係數的影響較明顯；而質量速度效應則對在高乾度時的熱傳係數會有較大的影響，且R-1234ze和R-134a幾乎擁有相同的熱傳係數。壓降部分，在相同的實驗條件之下，R-1234ze壓降皆會高於R-134a的壓降。微鰭管熱傳係數與壓降皆比平滑管高，在質量速度為100kg/m2s時微鰭管增益最好。 本研究之實驗數據與前人之熱傳經驗式及壓降經驗式比對的結果，Wu和Liu and Winterton關係式分別能預測於微鰭管與平滑管內之熱傳係數在±50%之內；Filho與Collier and Thome關係式分別能預測於微鰭管與平滑管內之壓降，其誤差範圍在±50%內。

The characteristics of convection boiling heat transfer coefficients and two-phase flow pressure drops were measured for R-134a and R-1234ze flowing in micro-fin and smooth tube with outer diameter of 9.52 mm. The range of mass flux is between 60 to 200 kg/m2s, heat flux ranging from 5 to 15 kW/m2, evaporating temperature ranging from 10℃ to 20℃. Results showed that the heat transfer coefficients of R-134a and R-1234ze increase with mass flux, heat flux, quality and saturation temperature. The effect of heat flux on the heat transfer coefficient is significant at low vapor quality, the effect of mass flux on the heat transfer coefficient is significant at high vapor quality, and the heat transfer coefficient of R-1234ze shows the same trend of R-134a. For the pressure drop, under the same experimental conditions, the pressure drop of R-1234ze is higher than that of R-1234ze.The heat transfer coefficient and pressure drop in micro-fin tube are both larger than that in smooth tube. Enhancement of micro-fin to smooth tube is better at mass flux of 100 kg/m2s. Between experimental data and correlations proposed for the heat transfer coefficients, Wu correlation can predict data in micro-fin tube within 50%. Liu and Winterton correlation can predict data in smooth tube within 50%. For the pressure drops, Filho correlation can predict the data within 50% in micro-fin tube. Collier and Thome correlation can predict the data within 50% in smooth tube.