冷媒R-134a與HFO-1234yf在平滑管內之流動沸騰熱流分析與比較

Abstract

本研究以實驗方法探討冷媒R-134a及HFO-1234yf於內徑3.9mm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200-500kg/m2s，熱通量為5.67-26.18kW/m2，飽和溫度為6℃-15℃。實驗結果顯示，R-134a與HFO-1234yf的熱傳係數均會隨著質量速度、熱通量、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是大的；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HFO-1234yf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-134a壓降皆會高於HFO-1234yf的壓降。 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，Wattelet和Chato關係式能預測於平滑管內之熱傳係數在50%之內；Friedel之壓降經驗式預測性最佳，其誤差範圍在±30%內。

The characteristics of convection boiling heat transfer coefficients and two-phase flow pressure drops were measured for R-134a and HFO-1234yf flowing in smooth tube with inner diameter of 3.9 mm. The range of mass flux is between 200 to 500 kg/m2s, heat flux ranging from 5.67 to 26.18 kW/m2, evaporating temperature ranging from 6℃ to 15℃. Results showed that, the heat transfer coefficients of R-134a and HFO-1234yf increase with mass flux, heat flux and saturation temperature. The effect of heat flux on the heat transfer was large at low vapor quality, the effect of mass flux on the heat transfer was large at high vapor quality, and the heat transfer coefficient of HFO-1234yf is almost same as that of R-134a. For the pressure drops, under the same experimental conditions, the pressure drops of R-134a are higher than that of HFO-1234yf. Between experimental data and correlations proposed for the heat transfer coefficients, Wattlet and Chato’s correlation can predict data in smooth tube within 50%. For the pressure drops, Friedel’s correlation can predict the data within 30%.