具階梯之封閉盒的熱質自然對流現象討論

Natural Convection Heat and Mass Transfer in an Enclosure with Steps

康明方(Ming-Fang Kang)

指導教授 ： 王立文

元智大學/工程學院/機械工程學系/碩士(2004年)

摘要

本研究主要乃藉實驗方法來探討幾何形狀一左、右邊界為階梯形狀的封閉盒，其由溫度梯度與濃度梯度所引起的熱質自然對流現象。左、右邊界之上下方由銅板所組成而階梯則為絕緣、絕熱之壓克力板。而實驗區域，利用其幾何形狀與邊界條件的設計，使得在實驗中可以觀察到背向階梯(backward-facing steps)與前向階梯(forward-facing steps)兩種情況下，並針對相關無因次參數來探討封閉區域內流場結構影響。
實驗工作流體為硫酸銅水溶液( CuS04 + H2SO4+ H2O )。溫度梯度由兩個不同溫度的恆溫水槽維持，濃度梯度則由電化學系統來建立，於銅板加上端電壓，使其成為電極造成濃度梯度。
對於封閉盒內流場現象，乃是採用雷射光暗影(shadowgraphy)來觀察流場，並以相機拍照紀錄以利分析。為了瞭解流場結構，對流場的溫度及濃度分佈亦做量測。最後，對於質傳遞率Sh值與Grm、Grt之關係也做量測與分析。
本實驗中無因次參數研究範圍如下：
Pr=7~8 ,Sc=1700~2500 ,s*=0.5 ,Grt=9.25×105~1.85×106 ,Grm=5.59×106 , =3.02~6.03

關鍵字

熱質自然對流 ； 封閉盒 ； 背向階梯 ； 前向階梯

並列摘要

The purpose of present study is to investigate flow pattern, temperature and concentration distributions resulting from buoyancy force due to a combination of temperature and species convection effects in an enclosure with steps.
In this experiment, the temperature and the concentration differences are made between two right and left copper walls and the step is made of Plexiglas to simulate. Cupric Sulphate solution is selected as the working fluid. Two constant temperature baths keep the temperature gradient. Concentration gradient is controlled via electrochemical system. The temperature and concentration gradients were imposed in such a way that their effects on the flow were either cooperating or opposing. 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 numbers.
To understand the flow structure, the temperature distribution and concentration distribution will be investigated. Finally, the correlations between Sherwood number and solutal concentration Grashof number and thermal Grashof number are also needed to be analyzed.
The range of the parameters in this study are
Pr=7~8 ,Sc=1700~2500 ,s*=0.5 ,Grt=9.25×105~1.85×106 ,Grm=5.59×106 , =3.02~6.03

並列關鍵字

thermosolutal convection ； enclosure ； backward-facing steps ； forward-facing steps

參考文獻

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