利用熱像液晶粒子研究具斜角的側面冷卻對高優態二元溶液凝固過程雙擴散對流形成之影響

Using thermochromic liquid crystal slurries to investigate the effect of a slanted cooling wall on the development of double-diffusive convection during the solidification of a liquid super-eutectic binary solution

張晉瑋(Chin-Wei Chang)

指導教授 ： 施陽正

國立臺北科技大學/機電學院/能源與冷凍空調工程系碩士班/碩士(2012年)

https://doi.org/10.6841/NTUT.2012.00587

摘要

二元溶液的凝固過程之應用範圍相當廣泛，如海洋科學、矽晶體的生長凝固過程、空調系統的儲冰過程、食品工業的製程與冷藏、合成金屬材料鑄造及低溫生物科技應用等等，其中凝固過程由溫度及濃度梯度引起自然對流現象也稱為雙擴散對流，此現象容易造成合金鑄造過程材料不佳，所以雙擴散對流形成原因及如何消除或減弱一直是過去研究的重點。本論文是利用實驗方式探討具斜角的側面冷卻對二元合金溶液凝固過程雙擴散對流行程之影響，實驗方面利用25%高優態氯化氨-水溶液為實驗樣品，實驗主要分為三大部分:PIV速度場觀測、熱像液晶溫度場觀測、紋影法之流場可視化。由實驗結果顯示，凝固過程中混合區會不斷釋出含水濃度高的低溫氯化氨-水溶液，使熱像液晶呈現紅色狀態，並搭配影像處理軟體使溫度場量化；斜角對於雙擴散對流有明顯的影響，0、5度與10、15度的成長過程大不相同，實驗結果可看出斜角角度大的填盒過程較快，使流場越快達到穩態。

關鍵字

二元溶液雙擴散對流 ； 側面冷卻方向凝固過程 ； 熱像液晶 ； 紋影法

並列摘要

Solidification of liquid binary alloys is found in various industrial applications, such as marine science, silicon crystal growth process, the ice storage system in HVAC, the food processing and cold storage in food industry, the metal alloys casting and low-temperature biotechnology applications. The natural convection phenomenon, also known as double-diffusive convection, which occurs during the solidification process owing to the effects of temperature and concentration gradients, is likely to cause poor quality of alloy castings. The factors contributing to the formation of double-diffusive convection and the means to eliminate or weaken such phenomenon have been the focus of research in the past. This study focused on the effect of slanted lateral cooling wall with negative slope on the formation of double-diffusive convection during the solidification of a 25 wt. % hyper-eutectic binary solution (NH4CL-H2O). Particle Image Velocimetry (PIV) techniques, thermochromic liquid crystal (TLC) and Schlieren method were employed to observe the flow development of the binary solution in the liquid. The experimental results showed that the water-rich fluid was continuously released through the mushy layer during solidification, resulting in the formation of a red color layer on the thermochromic liquid crystal. The image processing software was used for temperature field visualization. The experimental results also indicated that the lateral cooling wall with different slope has significant effects on the formation of double-diffusive convection during solidification. The growth process of double-diffusive convection varies apparently between the lateral cooling walls with higher slopes, such as in the case of 0 and 5 degrees compared to those with lower slopes, such as in the case of 10 and 15 degrees. As the slope of lateral cooling wall decreases, the filling-box process becomes faster and the time for the flow development to reach steady state becomes shorter.

並列關鍵字

Binary alloy ； Double-diffusive convection ； Lateral cooling solidification process ； Thermochromic liquid crystal ； Schlieren method

參考文獻

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[41] 葉佳陞，“垂直方向週期性振動對二元合金溶液單一方向凝固過程雙擴散對流形成之影響”，國立台北科技大學碩士論文，中華民國100年6月。

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