本實驗研究是將質量傳遞引入方形管道之主流中,在不同的傾斜角度及 強制對流效應之下進行質混合對流研究。在此,混合對流係指利用幫浦所 造成的強制對流,在速度完全發展之後,與質傳所形成的自然對流合併之 流體運動現象;全實驗可分為三部份進行討論,第一部份為傾斜角度等於 零,第二部份為傾斜角度大於零,第三部份為傾斜角度小於零之質混合對 流研究。各部份再分為(A)上板陽極、下板陰極;(B)上板陰極、下板 陽極來進行研究。實驗時所使用的工作流體為硫酸銅水溶液(CuSO4+H2 SO4+H2O),質量傳遞是由電化學系統,在測試區之上下銅板加上端電壓 ,正極為陽極板,負極為陰極板。陽極板產生氧化反應而解離出銅離子, 陰極產生還原反應而析出銅。藉此達成濃度梯度之建立。流場觀察採用雷 射光暗影法(shadowgraph)作觀察及照相記錄。並量測極限電流,以計 算質傳遞率。實驗的無因次參數範為如下: Ar=1 Sc=1700~2400 Pr=5.0~7.0 Re=100~700 Gr,m=1.27×106 由流場觀察顯示: Case(A)之邊界屬於質不穩定,流場為質混合對流的流場型態,而 Case (B)之邊界屬於質穩定,流場為強制對流的流場型態,不會有二次流產 生。而當傾斜角度大於零之Case(A)的情況下,上板產生與主流方向相 反之分力,下板產生與主流方向相同之分力。而當傾斜角度小於零之Case (A)的情況下,上板產生與主流方向相同之分力,下板產生與主流方向 相反之分力。 質傳遞率量測:Case(A)及Case(B)質傳遞率 Sherwood值在傾斜角度大於零時,因陰極板對流效效應增加而增加,而傾 斜角度小於零時質傳遞率Sherwood值因陰極板對流效效應減弱而變小。
An experimental study of mixed convection mass transfer flow of a solution in an inclined channel is performed with an electrochemical system. The purpose of the present study is to investigate laminar fully developed flow between two horizontal and inclined plates with concentration gradients. The experiments would be divided into three parts:(1)inclined angle θ=0(2) inclined angle θ>0 (3) inclined angle θ<0.For mass convection, the types of the boundary of test section are: (a) top plate is anode and bottom plate is cathode (b) top plate is (b) cathode and bottom plate is anode.To visualize the flow, the shadowgraph technique is used. Electrical measurements are used to obtain mass transfer rates and to infer Sherwood numbers. The ranges of the parameters studied in the present work are Ar=1, Sc=1700~2400, Pr = 5.0~7.0, Re=100~700, Gr,m=1.27(106, From the flow visualization, we can find:The flow with the boundary of type (a) of test for mass convection belongs to mass transfer mixed convection, type (b) belongs to forced convection.Mass transfer rate measurements:For mass convection, the mass transfer rate for the two types of tests increases with increasing Re for a fixed Ra,m and increases with increasing inclined angle for fixed Re and Ra,m