絕緣壁具雙凸塊封閉盒之熱質自然對流現象探討

Natural Convection Heat and Mass Transfer in an Enclosure with Two Blocks along the Adiabatic Walls

郭進倫(Chin-Lun Kuo)

指導教授 ： 王立文

元智大學/工程學院/機械工程學系/碩士(2006年)

https://doi.org/10.6838/YZU.2006.00054

摘要

本研究主要乃藉由實驗方法來探討幾何形狀為一正方形的封閉盒，其由溫度梯度與濃度梯度所引起的熱質自然對流現象。左、右邊界由銅板所組成而上、下板與凸塊則為絕緣之電木板。本次的實驗區域，利用其幾何形狀與邊界條件的設定，藉由改變開口比Ap及傾斜封閉盒，使得在實驗中可以觀察到凸塊效應，並針對不同Gr,t、Gr,m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( CuSO4 + 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。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Gr,m、Gr,t之關係做量測與分析。
實驗結果顯示，傾斜角度對流場質傳遞率有顯著影響。對傾斜角度而言，會造成降低質傳遞率。而無傾斜角度時，由於產生之質柱狀流(solutal plume)及鹽手指(salt finger)現象會造成質傳遞率增加。

關鍵字

熱質自然對流絕緣璧 ； 封閉盒 ； 凸塊

並列摘要

The purpose of present study is to investigate flow pattern, temperature and concentration gradients resulting from buoyancy force due to a combination of temperature and species convection effects in an enclosure with blocks. Effect of Gr,t, Gr,m and blocks is the main objective in this study.
The test cell is a square enclosure formed with acrylic ,Bakelite and copper plates, which is wrapped with block Bakelite insulator to ensure an adiabatic boundary condition.
In this experiment, the temperature and concentration differences are made between two right and left copper walls and the blocks are made of bakelite simulate. We use copper sulphate-sulfuric acid solution as the working fluid. Two constant temperature baths sustain the temperature gradient. The concentration gradient is controlled via an electrochemical system. In order to visualize the flow, the shadowgraph technique is used. Electrical measurements will be used to obtain mass transfer rates to infer Sherwood numbers.
To understand the flow structures, the temperature distribution and concentration distribution will be investigated. Finally, the correlations between the Sherwood number, the solutal Grashof number, the thermal Grashof number will also need to be analyzed. The effects of the blocks will be investigated carefully.
It is demonstrated that Sh decreased with increasing inclination angle for fixed Gr,m value. This is because
the increasing inclination angle results in decreasingly
solutal plumes and finger type flow and,hence, monotonically decreasing Sh.

並列關鍵字

Heat and Mass Convection ； Adiabatic Walls ； Enclosure ； Blocks

參考文獻

1. S. Ostrach, "Natural Convection with Combined Buoyancy

Graphical Curiosity the Perpetual Salt Fountain", Deep

pp.183-200, 1968.

Gradients", Int. J. Heat Mass Transfer, Vol.28, No.1,

pp. 165-173, 1985.