具斜角的側面冷卻對二元合金溶液凝固過程雙擴散對流形成之影響

The Lateral Cooling Effect of the Side Wall with Slanted Surface on the Development of Double-diffusive Convection during the Solidification of a Liquid Binary Alloy

徐郁筠(Yu-Yun Xu)

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(2009年)

https://doi.org/10.6841/NTUT.2009.00200

摘要

二元溶液的凝固過程之應用範圍很廣，如化學工業，地質學(土壤和岩石的凍結)，和食品工業(食品的製程和前處理)、合成金屬材料的鑄造、儲能系統的儲冰過程以及低溫生物科技的應用等等，其中凝固過程中雙擴散對流形成的原因及如何消除或減弱雙擴散對流的現象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形成之影響，觀察雙擴散對流所造成之A型缺陷，實驗方面是以27 %的高優態氯化氨-水溶液為研究樣品，實驗主要分為五大部份：PIV流場觀測、暗影法流場可視化、固液界面位置量測、溫度分佈量測與濃度分佈量測。實驗結果顯示，由PIV流場觀測、暗影法流場可視化可知隨著凝固時間增長，雙擴散對流現象越穩定，斜角0度、5度、10度隨著角度越大，雙擴散對流現象越紊亂，斜角15度的雙擴散對流現象產生最慢，循環流下降最快，流場較快達穩定；從混合區釋放出液體產生雙擴散對流之處，溫度下降快速；斜角角度越大，濃度分佈越快達到較均勻。

關鍵字

質點影像速度儀 ； 二元溶液 ； 雙擴散對流 ； 側面冷卻方向凝固過程

並列摘要

Phase change materials were employed in industrial applications very often. The solidification of a binary solution is one of them (for example, casting of binary alloys). In the past, one of the main issues to study the solidification of a liquid binary alloy focused on the development of “double-diffusive convection” because it is the main reason to cause the poor quality of alloys. The objective of this study is to investigate the effect of the slope of the side wall on the development of double-diffusive convection. An aqueous solution of 27 wt.% NH4Cl, with a liquidus temperature corresponding to 18.9℃, was adopted as the test sample in this study and it was put into an enclosure cooled from the lateral side to investigate the flow field, heat and mass transport phenomena during solidification. Experiments conducted in this study include PIV measurement on the flow field, flow visualization by shadowgraph technique, measurement of the growth of the mushy zone with time, transient temperature distribution within the test cell and the concentration distribution within the cavity. According to the experimental results of PIV measurement and flow visualization by shadowgraph, the development of double-diffusive convection became stable at later stage of solidification. Four kinds of slopes of the side wall were employed in this study, including 0, 5, 10 and 15 degrees. The larger the slope is, the earlier the double-diffusive convection occurred among the slopes of 0, 5 and 10 degrees. However, the double-diffusive convection grew the slowest for the slope of 15 degrees.

並列關鍵字

Particle Image Velocimetry (PIV) ； Binary Solution ； Double-diffusive Convection ； Lateral Cooling

參考文獻

[1] Lock, G.S.H., 1996, “Latent Heat Transfer: an Introduction to Fundamentals,” Oxford University Press.

[3] Flemings, M.C., 1974, “Solidification Processing,” McGraw-Hill Inc., New York.

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