- 學位論文
萊氏現象之自動化量測與分析
Automatic measurement and analysis of Leidenfrost phenomenon
摘要
本研究主要目的在建立一套萊氏實驗的自動化量測系統。此系統是以圖形化語言LabVIEW軟體為核心，進行資料擷取、程式編輯以及儀器控制。系統分為四個部份，分別為溫度控制、液滴控制、影像擷取以及影像處理。溫度控制部份是採用比例-積分-微分（PID）控制演算法，以Ziegler-Nichols的PID調校法則取得PID參數；以RS-232傳輸介面連結注射筒幫浦及電腦，並由電腦控制幫浦流速及流量；液滴蒸發過程中，以LabVIEW經由視訊裝置擷取液滴蒸發時的影像。由LabVIEW影像處理程式讀取儲存的液滴影像，經過濾波、二值化等影像處理過程，取得液滴蒸發時間，繪成蒸發曲線圖。 本研究中，以手動方式進行純水、氧化鋁及二氧化鈦奈米流體的萊氏實驗，與純水相比較，奈米流體之萊氏溫度增加並且減少萊氏蒸發時間，且0.1% TiO2奈米流體液滴具有較長的萊氏蒸發時間。另外，也以完成的自動化量測系統進行數種液體之萊氏實驗。IPA與純水相比較，具有較低的萊氏溫度點及較長的蒸發時間，並且有隨著濃度越高其萊氏溫度點越低及萊氏蒸發時間越長的趨勢。影像處理結果與實際蒸發曲線比較，萊氏溫度點約相差±5oC，萊氏蒸發時間誤差約在0.6至2.4秒，而萊氏時間的均方根誤差為1.1至5.5秒之間。
並列摘要
The principal purpose of this investigation is the Leidenfrost experiment for different testing liquids and heating surfaces by building an automatic measurement system. The system is LabVIEW based, and performs data acquisition, program editing, and instrument control. The system has four different parts: temperature control, droplet control, image acquisition and image processing. The temperature control consists of a PID controller, with Ziegler-Nichols Tuning Rules for PID parameters. Connecting a syringe pump and a computer via RS-232 interface, the computer control the size of droplets. During the droplet evaporation, the images are grabbed via webcam and transmitted to the system. Then, saved images are processed by LabVIEW image processing module. Through these images from image processors such as filter, threshold…etc., then the evaporation time of droplet can be found and the evaporation curves can be made. In this investigation, aluminum oxide and titania nanofluids are used to perform the Leidenfrost experiments manually. Compare with the pure water, it can be found that the Leidenfrost temperature of nanofluid increases, and the Leidenfrost evaporation time decreasea. Furthermore, the 0.1% of titania nanofluid droplet has longer period of Leidenfrost evaporation time. Then, Leidonfrost experiments are performed by completed automatic measurement system. Comparing with the IPA solution with the pure water, IPA has lower Leidenfrost temperature and longer evaporation time. Moreover, it also has a tendency that when the concentration of the IPA goes up, the Leidenfrost temperature goes down and the Leidenfrost evaporation time becomes longer. Comparing evaporation time derived from the image process with that from human observation, it can be found that the accuracy of the Leidonfrost temperature is ±5oC, and the accuracy of the Leidonfrost evaporation time is between 0.6 and 2.4 second. Also, the root mean square of the Leidonfrost evaporation time is between 1.1 and 5.5 second.
參考文獻
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