- 學位論文
渦卷膨脹器於有機朗肯循環之實驗探討與數值分析
Experimental investigation and numerical analysis of scroll expander for the application in organic Rankine cycles
摘要
本研究主要探討渦卷膨脹器應用於有機朗肯循環(Organic Rankine Cycle, ORC)的性能及匹配性分析，並利用CFD技術探討其內部流場行為；其研究方法主要分為實驗及數值模擬。實驗分為三階段，第一階段將體積比2的渦卷膨脹器於ORC中做各項機械摩擦測試、內部洩漏測試，並利用膨脹器效率為指標探討各項損失對膨脹器性能之影響；第二階段實驗使用入口過熱度做為控制變數，使用Vr_2與Vr_4之渦卷膨脹器進行實驗，其膨脹器效率隨系統過熱度增加而上升，並且發現最佳的過熱操作溫度為12?C；第三階段的實驗，使用Vr_3的渦卷膨脹器進行出口壓力對性能的影響，發現出口壓力愈高時其效率愈佳；最後利用三種不同Vr的渦卷膨脹器於ORC系統在不同膨脹器出入口之間的壓力差與膨脹器轉速進行性能測試，目前測得膨脹器最高效率為79%。在CFD模擬部分與實驗值驗證後，首先以壓力分佈圖探討渦卷膨脹器內部行為與現象。發現在Vr_2的膨脹器中，存在壓力不平衡的現象；另外在同樣壓力差下，愈高體積比的渦卷膨脹器於膨脹過程中，壓力下降的趨勢會愈來愈高。第二階段使用R134a與R245fa作為工作流體，以Vr_4的渦卷膨脹器作比較，發現在使用R134a時可得到較高的效率及輸出功率，但是在膨脹器出入口之壓力差不夠時會出現過膨脹現象(Over expansion)，最後更改體積變化率探討在相同體積比與吸氣體積對膨脹器之影響，其膨脹器效率隨體積變化率增大而變小，並且由壓力分佈圖得知，愈高的體積變化率使得壓力分佈趨勢會下降的愈快。
並列摘要
The present study mainly investigates the performance of scroll expander and its being applied in the organic Rankine cycle (ORC). Experiments using ORC loop to test and investigate the performances of the scroll expanders and the cycle have been conducted. CFD (Computational Fluid Dynamics) simulations have been also implemented to get insight of the behavior and the phenomena during expansion process. In the experiment, an expander with built-in volume ratio (Vr) of 2 has first of all been used to implement the tests of mechanical friction and interior leakage in order to understand the influences in efficiency. Secondly, both Vr_2 and Vr_4 expanders were used to conduct the influence of the superheating at the inlet. The results indicate the optimal expander efficiency exists at around 12?C higher than the saturated temperature. Thirdly, experiment measurements by varying the outlet pressure using Vr_3 scroll expander were performed. Results indicated that higher expander outlet pressure results in higher expander efficiency. At last, Vr_2, Vr_3 and Vr_4 expanders were installed in ORC loop to conduct the influence of pressure difference between inlet and outlet, and the rotating speed of expander. So far, a maximum expander efficiency of 79% has been found. In CFD simulations, verifications by the comparison between the experiment data and CFD simulation results have been completed. P-V(θ) diagram indicates the internal flow behavior and points out that the expanders with higher built-in volume ratio induces greater pressure drop from inlet to outlet. An unbalance phenomenon in pressure exists in the expansion chamber for Vr2 scroll expander. Secondly, Vr4 scroll expander was used to compare the performance when R134a and R245fa were employed as working fluid. The results show that the use of R134a has higher efficiency and power output. However, the phenomena of over-expansion might happen if the pressure difference between inlet and outlet is too small. Finally, under the conditions of specific built-in volume ratio and suction volume, the study indicates that the increase in the rate of volume change during expansion process results in the decrease in expander efficiency.