上熱下冷的垂直溫度梯度與水平濃梯度之自然對流研究

Experimental Study of Thermosolutal convection in Rectangular Enclosures with Vertical Tmperature and Horizontal Concentration Gradients

盧明初(Lu, Ming Chu)

指導教授 ： 王立文

元智大學/工程學院/機械工程學系/碩士(1995年)

摘要

本研究目的是以實驗方法探討矩形密閉盒內，由上熱下冷的垂直溫度梯度
與水平濃度梯度所共同引起的熱質自然對流現象，對於不同的浮力比及展
弦比所展現的流場層化型態及盒內溶液溫度與濃度的變化情形均是研究的
對象。本研究的動機起因於自然界中有許多為熱質對流所引起規律性的層
化現象，以及環境污染問題日趨嚴重，因此在污染源散佈過程中層化現象
的流場型態，有必要作深入的分析探討。實驗裝置是以銅板及壓克力板構
成各種展弦比之矩形盒，銅板外部以泡沬絕緣材料包裹。工作流體為硫酸
銅水溶液，加入硫酸為輔助電解質。實驗中溫度梯度是由兩個不同溫度之
恆溫水槽來維持，使上板為熱板，下板為冷板。濃度梯度是由電化學的方
法來造成，即利用電解方式在兩銅板附近形成不同濃度的邊界層。對於盒
內流場現象採用雷射光暗影法或輔以加入質點的質點光幕法來觀察流場，
並以相機拍攝以利分析。為瞭解流場結構，對流場的溫度與濃度分佈亦作
量測。其中濃度的量測是使用35mW的雷射光為光源，利用雷射光穿透過工
作流體時，由強度的衰減，換算溶液的濃度。最後，對於質傳遞率Sh值與
Gr,t，Gr,m之關係，也進行量測與分析。

關鍵字

熱質對流 ； 溫度梯度 ； 濃度梯度

並列摘要

The purpose of this study is to investigate the
transportphenomena of thermosolutal convection in
rectangularenclosures with vertical temperature and
horizontalconcentration gradients. The current study isprimarily
motivated to gain a better understandingof the multi-layer flow
structure caused bythermosolutal convection. The test cell is
arectangular enclosure formed with acrylic andcopper plate,
which is wrapped with foam insulatorto ensure an adiabatic
boundary condition. Thetemperature gradient is maintained
uniform andcontrolled by two separate constant-temperature
baths,which circulate heated or cooled water through theheat
exchanger. The working solution used is aqueouscopper sulphate.
An electrochemical method based ona diffusion-controlled
electrode reaction will beemployed in this work for creating the
concentrationgradient. Flow visualization has been
accomplishedusing the particle tracer and shadowgraph technique.
Both the temperature and concentration distributionat different
time are quantitatively measured. Theconcentration distribution
of cupric ions in thesolution is determined by measuring the
attenuationof light through the test cell with a 35mW He-Ne
laseras the light source. According to Beer's law
theconcentration of a solution is proportional to anabsorbency,
which is defined as the logarithm of theratio of input and
output light intensities. Finally,the relations between the
dimensionless mass transferrate Sh and Gr,t as well as Sh and
Gr,m are discussed.

並列關鍵字

Thermosolution Convection ； Temperature Gradient ； Concentration Gradient