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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/2427

    Title: 雙重溫度與濃度梯度下多孔性介質中磁流體之雙擴散對流現象;Hydromagnetic Double-diffusive Convection In A Porous Medium With Opposing Temperature And Concentration Gradients
    Authors: 曾家麟;Chia-Lin Tzeng
    Contributors: 機械工程研究所
    Keywords: 磁流體;多孔性介質;雙擴散對流;double-diffusive convection;hydormagnetic;porous medium
    Date: 2004-06-28
    Issue Date: 2009-09-21 11:46:34 (UTC+8)
    Publisher: 國立中央大學圖書館
    Abstract: 本文利用數值模擬研究多孔性矩形封閉空間中,雙重溫度與濃度梯度下磁流體之雙擴散對流現象。多孔性介質內部考慮黏滯效應、慣性力與浮力效應之影響。定義上、下壁面為絕熱,左、右壁面為固定溫度與固定濃度,並在橫向上施加一均勻不隨時間變化之磁場作用於流場。這個受磁場影響的流場,我們指定研究浮力比(buoyancy ratio)範圍N=0~2.0,普朗特數(Prandtl number Pr=1.0~5.0,路易士數(Lewis number)Le=0.1~2.0,瑞里數(Rayleigh number),以及設定此封閉區域的長寬比例為2:1、達西數(Darcy number)Da=10-5~10-1與孔隙率(porosity)ε=0.2~0.8。受磁場影響之流場熱質傳變化會因磁場大小不同而增大或降低。本文研究之結果,熱質傳的變化受到不同普朗特數、路易士數、浮力比、內部熱源、滲透率(permeability)、孔隙率,瑞里數與哈曼數(Hartmann number)之大小不同,高溫壁面平均之紐塞爾數(Nusselt number)與希吾爾德數(Sherwood number)的變化亦不同。 在暫態研究方面,流體依其熱慣性(thermal inertia)的不同,配合高瑞里數之條件下,流場流動會呈現不同程度之震盪變化,在磁場強度增強下會抑制這種現象,使流動震盪減緩並較快達到穩態。 本研究在瑞里數RaT=105下,將高溫壁面之平均紐塞爾數與平均希吾爾德數對磁場及孔隙率之關係統計成一半經驗式(correlation),期望提供工業界從事類似研究之先進一參考性的指標。 The problem of hydromagnetic double-diffusive convective flow of a binary mixture in a porous rectangular enclosure is solved numerically in this work. The effects of viscosity and inertial force of the porous medium are considered. The upper and lower walls are insulated. Constant temperatures and concentrations are imposed along the left and right walls of the porous enclosure and a uniform magnetic field is applied in the x-direction. The buoyancy ratio is in the range of 0.0~2.0, Prandtl number in 1.0~5.0, Lewis number in 0.1~2.0, Rayleigh number in 105~107, Darcy number in 10-5~10-1, porosity in 0.2~0.8 and the enclosure aspect ratio is fixed at 2.0. Results for various conditions were presented and discussed. It is found that the flow structure and heat transfer characteristics inside the enclosure depend strongly on the porosity, permeability, the magnetic field, the effect of buoyancy and the thermal inertia. The effect of the magnetic field is found to reduce the movement of the convection within the enclosure. For the unsteady case, the flow oscillates periodically at high Rayleigh number and high heat capacity ratio. The application of magnetic field reduces the oscillation. Finally, this work provides correlations of the Nusselt number vs. porosity and the Hartmann number.
    Appears in Collections:[機械工程研究所] 博碩士論文

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