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

The Impact of Periodic Vibration in Vertical Direction on the Development of Double-Diffusive Convection of a Liquid Binary Alloy during the Unidirectional Solidification Process

葉佳陞(Jia-Sheng Ye)

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(2011年)

https://doi.org/10.6841/NTUT.2011.00523

摘要

二元合金溶液的凝固過程已有多年的研究，且凝固過程有廣泛的應用，如食品工業的製程及冷藏，利用潛熱的儲能及儲冰系統、製造業的合成金屬鑄造過程，材料科學的應用、化學工業、地質學(土壤和岩石的凍結)、以及低溫生物科技應用等等。凝固過程中會形成雙擴散對流，雙擴散對流的形成將對整個凝固過程造成不良的影響，如何消除或減弱雙擴散對流一直是研究的重點。本論文研究目的是利用實驗方式研究垂直方向週期性振動對單一方向二元合金溶液凝固過程雙擴散對流形成之影響，希望能達到消除或減弱雙擴散對流的目標。本實驗使用27%的高優態氯化氨-水溶液為實驗樣品，以改變振動頻率及振幅兩種振動方式研究底面冷卻的單一方向凝固過程熱質傳現象。本實驗主要分為四大部分：暗影法流場可視化、流道分佈及火山口直徑量測、固液界面高度量測、溫度分佈量測。由實驗結果可知，改變振動頻率及固定振幅實驗，提高頻率對柱狀雙擴散對流的抑制效果不佳，而固定振動頻率且提高振動振幅可有效的抑制柱狀雙擴散對流的形成。

關鍵字

二元合金溶液 ； 雙擴散對流 ； 單一方向凝固過程 ； 週期性振動

並列摘要

Solidification of binary solutions is employed in industry very often. Casting of binary alloys is one of them (for example, casting of binary alloys, ice storage system). In the past, one of the main studies focused on how to eliminate or weaken double-diffusive convection during solidification because double-diffusive convection was the main reason to cause poor material quality in the final ingots. The purpose of this study is to investigate the periodic vibration in the vertical direction on the development of double-diffusive convection during solidification. A hyper-eutectic binary solution (NH4Cl-H2O) was adopted as the test sample in this project and it was put into an enclosure cooled from the bottom, known as unidirectional solidification process, to investigate the heat and mass transport phenomena during solidification. The experiments conducted in this study included flow visualization by shadowgraph, measurement of channel size and channel distribution, transient temperature distribution and movement of the solid/liquid interface. Experimental results show that the increasing of the frequency does not give any significant suppression effect on the formation of the plume-type double-diffusive convection. However the increasing of amplitude can effectively suppress formation of the plume-type double-diffusive convection.

並列關鍵字

Liquid binary alloys ； Double-diffusive convection ； Unidirectional solidification process ； Periodic vibration

參考文獻

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[8]P.J. Prescott, and F.P. Incropera, “Convection Heat and Mass Transfer in Alloy Solidification”, New York, Academic Press, Advances in Heat Transfer, Vol. 28, 1996, pp. 231-338.