近年為了提升有機朗肯循環的效率運用於中低溫熱能轉換，目前學術界多朝穿臨界流體循環進行研究。本論文欲探討計畫使用於穿臨界有機朗肯循環的工作流體新型冷媒NOVEC 649在近臨界點的熱傳現象。本研究設計一個新型冷媒NOVEC 649的封閉循環，探討該流體於内徑1mm、外徑25mm、長度20cm的迷你銅製傾斜流道中，穿臨界狀態時之性質變化與熱傳現象。NOVEC 649之臨界壓力為18.7 bar，臨界溫度為 441.8 K。實驗操作參數為進口壓力19~23bar，進口雷諾數3039~51543，質量通率707.4~1061 kg/m2s，流道傾斜角度有θ=0∘水平流動、90∘垂直向上流動、-90∘垂直向下流動、-30∘、-45∘、-60∘。於此實驗探討流體在穿臨界時根據不同壓力、質量流率、傾斜角度與流向之實驗操作參數組合，性質的劇烈變化對於熱傳產生之效應。結果顯示，壓力效應對於熱傳係數之影響不如流量效應明顯。在此實驗相對較小的流量時，會在假臨界溫度附近有熱傳惡化的發生，反之相對較大的流量時，會有熱傳增加的現象。此外，從不同傾斜角的熱傳係數比較中發現，向下流熱傳的確如前人文獻所述會比向上流好。接著，引用相關文獻提出之無因次參數進行浮力效應與加速度效應之分析，並提出適用於傾斜管之浮力效應無因次參數判斷門檻值，結果顯示大部分的實驗數據點浮力效應皆可忽略，而垂直管的加速度效應十分強烈。最後，根據此實驗數據發展適用之經驗式，在經驗式中導入傾斜角度θ，以利運用於各種流道傾斜狀況與流向，有別於過去相關文獻僅針對不同傾斜角度發展個別之經驗式，並與實驗數據比較之誤差約為±30%。

This paper focused on the buoyancy effect and acceleration effect on the heat transfer characteristics of supercritical NOVEC 649 in an inclined miniature tube, aiming to provide guidance for the vapor generator design in trans-critical ORC systems. Experiments on turbulent heat transfer by NOVEC 649 in horizontal, vertical, and inclined flow were conducted in a tube with an inner diameter of 1 mm. The experiments were performed for inlet pressures ranging from 19 to 23 bar, mass flux ranging from 707.4 to 1060 kg/m2s, and Rein from 3039 to 51534. These experiments demonstrate that the heat transfer coefficients are significantly influenced by mass flux instead of system pressure in this study. To determine the buoyancy effects and acceleration effect on heat-transfer characteristics, some dimensionless parameters such as ,Bu and Ac are compared with the related threshold values along the test section. New threshold values of buoyancy dimensionless parameter (Bu) for an inclined pipe are proposed. Results presented in dimensionless form illustrate the strong influence of acceleration effect and the ignorable influence of buoyancy effect on this study. Correlations have been developed for inclined flows with accuracy 30% (up to 95% of the 640 valid data points where predicted within the ±30% accuracy limits).

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