密閉矩形盒中具溫差之雙圓柱之自然對流現象

鄭偉駿

指導教授 ： 王立文

元智大學/工程學院/機械工程學系/碩士(2002年)

摘要

密閉矩形盒中具溫差之雙圓柱之自然對流現象
學生：鄭偉駿 指導教授：王立文
元智大學機械工程研究所
摘 要
本研究主要是藉助實驗方法來探討具雙圓柱矩形封閉區域中，溫度及濃度梯度所引起的自然對流之流場形態以及圓柱附近的垂直溫度分佈。
研究動機起因於結晶成長過程中組成不均勻的現象非常嚴重，因此對於過程中熱量及質量的傳遞應作充分了解。
本文所作實驗，將兩圓柱賦予溫度差和濃度差，其它邊界保持絕緣。所以，本研究又分兩部分：
（1） 矩形盒水平放置,即兩圓柱為一左一右之自然
對流現象。
（2） 矩形盒垂直放置,即兩圓柱為一上一下之自然
對流現象。
工作中工作溶液為硫酸銅水溶液。溫度梯度由兩個不同溫度的恒溫水槽來維持。濃度梯度是由電化學方法造成的，即利用電解方法形成不同濃度的邊界層。對於矩形密閉容器內流場現象，採用雷射光暗影（shadowgraphy）來觀察流場，並以相機拍照記錄以利分析。
順向流場在加入質傳後因為流體堆積的關係，通常會有interface的產生，而逆向流場在溫度傳遞速率與濃度傳遞速率不均勻的情況下通常會有鹽手指的產生。在質傳遞率方面，在固定Gr,m的情況下，當Gr,t增加時，質傳遞率(Sh)會隨之增加。且順向的質傳遞率比逆向的質傳遞率高。而在矩形盒垂直放置時質傳遞率又比矩形盒水平放置時質傳遞率高。
本實驗中
Ar=0.625 Gr,t=2.41 ×105 ~ 7.23 ×105
Gr,m=1.82 ×106 N=-2.52~7.55
Sc=1700~2300 Pr=6.0~7.0

關鍵字

雙圓柱

並列摘要

Thermosolutal Convection in a Rectangular Enclosure with Dual Cylinders
Student: Wei-Chun Jeng Adviser: Lin-Wen Wang
Department of Mechanical Engineering
Yuan-Ze University
ABSTRACT
The purpose of present study is to investigate flows pattern, temperature and concentration distributions resulting from buoyancy force due to a combination of temperature and species convection effects in a rectangular enclosure with dual cylinders inside.
In the process of crystal growth, the non-homogeneous phenomenon would become more and more serious. So to know the sufficient understanding of heat and mass transports is indispensable.
In this experiment, the temperature and concentration differences are made between two cylinders and the insulation is kept all over the margin. Cupric Sulphate solution is selected as the working fluid. Two constant temperature baths keep the temperature gradient. Concentration gradient is controlled via electrochemical system. In order to visualize the flow, the shadowgraph technique is used. Electrical measurements will be used to obtain mass transfer rates and to infer a Sherwood number. We can find that in the cooperating case, the interface is shown due to the fluid accumulation after imposing the mass transport. However, in the opposing case, the salt finger is found owing to the difference between the thermal diffusive velocity and mass diffusive velocity.
This study can be divided into two parts:
(1) The enclosure is placed horizontally, and convection is established where one cylinder is inserted right next to the other.
(2) The enclosure is placed vertically, and convection is established where one cylinder is inserted beneath the other.
The range of the parameters in this study are Ar=0.625
Gr,t=2.41 ×105 ~ 7.23 ×105 Gr,m=1.82 ×106
N=-2.52~7.55 Sc=1700~2300 Pr=6.0~7.0

並列關鍵字

HASH(0x8b2a1f8)

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