由於全球暖化效應之影響，全球變暖潛能值（GWP）較低之冷媒是目前工業及住宅空調使用上之趨勢。近年來，因冷媒R-32具有低GWP，充填量低且易回收等等之優點，目前已逐漸被許多空調製造商用來替代空調常用之冷媒R-410A。此外，冷媒R-32在空調上之性能研究也是近年來之重點項目。然而在目前相關文獻裡，冷媒R-32在飽和溫度10℃以下之兩相蒸發熱傳性能研究並不是很完全，且在冷凍系統(操作溫度在-20℃至-40℃)所使用之冷媒中，目前尚無人使用冷媒R-32來取代常用於冷凍系統之冷媒，如R404a等。因此，冷媒R-32在未來極有可能成為冷凍系統所使用之冷媒。在本實驗中，冷媒R-32在不同質量流率及熱通量之實驗條件下，進行圓管內兩相蒸發熱傳及壓降性能量測。測試段為套管式熱交換器，其內管管徑為5mm，操作溫度為10oC，並透過modified Wilson Plot方法先行計算冷媒R-32之單相傳熱係數及壓降，以確認本實驗系統之正確性。從實驗結果顯示，在不同質量流率及熱通量下，熱傳係數會隨著質量流率和熱通量的提升而提升，且在乾度大約為0.8時，因為管內部份乾涸而下降，顯示了在此實驗操作之溫度下，兩相蒸發熱傳性能與傳統兩相蒸發理論並無差異。同時，實驗結果也與傳統兩相熱傳經驗式相比，發現在不同質量流率下，因為各熱傳經驗式之沸騰模型或是其增強係數所考慮之參數有所差異，導致不同質量流率下所適用之熱傳關係式有所不同。此外，本實驗結果也將為下一步研究工作(冷媒R-32在圓管內之超低溫兩相蒸發熱傳及壓降性能測試)提供一個相關參考。;Due to the global warming effect considerations, refrigerants with lower value of the Global Warming Potential (GWP) will be the next generation refrigerants which are used in the industry and the residential air-conditioner. And now, a new developed refrigerant R-32, with GWP value of 675, has proposed to substitute refrigerant R-410A whose GPW value is 1975. Therefore, many major air-conditioning manufactures have determined refrigerant R-32 in their products and some studies have been discussed in recent years. However, the information of refrigerant R-32 on saturation temperature around 10°C is still insufficient, and the heat transfer performance of refrigeration system around -20°C to -40°C has not been clarified. In this study, two-phase heat transfer coefficient and pressure drops of refrigerant R-32 have been measured in a horizontal tube with 5.0mm inner diameter, and saturation temperature at 10°C with different heat flux and mass fluxes. The test section is a double pipe heat exchanger, where the refrigerant flows in the tube side and water flows in the annular side. Also by verifying the experimental rig worked well or not, modified Wilson Plot method were used to calculate the singe-phase heat transfer coefficient and pressure drops of refrigerant R-32. In this study, two-phase experiments were conducted at vapor qualities from 0.1 to 0.9 where mass fluxes from =200 kg/m2s to 600 kg/m2s and heat fluxes from = 26 kW/m2 to 46 kW/m2. The results show that the traditional two-phase knowledge works well and the correlations of Shah [2], Gungor and Winterton [3] and Liu and Winterton [4] had different accuracy in different flow conditions due to the enhancement factor in each flow boiling model are not the same. Besides, the results in this study can also be compared and discussed for the next step research of operating temperature go down at lower temperature.
