- 學位論文
磁性奈米流體在微管道內對流熱傳之研究
Study on the convective heat transfer of magnetic nanofluids in a microtube
摘要
本論文完成磁性奈米流體在微管道內熱流場及其特性之分析。主要目的在探討微管道管長、粒子體積分率及外部磁場強度對流體速度、溫度、壓力、壓降、流阻及熱傳率之影響。首先，我們完成水基磁鐵礦(Fe3O4)奈米流體之製備及其材料性質之測定。接著，應用質量、動量及能量守恆方程式並結合邊界條件，我們完成了熱流場模式的建立，該模式經實驗數據及理論結果之比較後得以驗證。最後，經由前進隱性法(MI)數值分析磁性奈米流體在微管道內熱流場及其特性。 研究結果發現，當管長增加時，速度、壓力及溫度場趨於完全發展，此時壓降趨於增加而平均流阻趨於固定。當粒子體積分率增加時，平均流阻增加而平均熱傳率減少。當外部磁場強度增加時，平均流阻增加，平均熱傳率在一般情形下亦增加。
並列摘要
This thesis conducts an analysis of the flow and thermal fields and their corresponding characteristics of the magnetic nanofluids in a microtube. The main purpose is to investigate the influences of microtube length, particle volume fraction, and external magnetic field strength on the fluid velocity, temperature, pressure, pressure drop, flow drag, and heat transfer rate. First, we complete the preparation of water-based magnetite (Fe3O4) nanofluids and the determination of their material properties. Further, we apply mass, momentum, and energy conservation equations as well as the boundary conditions to establish the thermal-flow field mode, which can be verified by the comparison of the experimental data with theoretical results. Finally, the flow and thermal fields and the correspeonding characteristics of nanofluids in a microtube are numerically analyzed by using the marching implicit (MI) method. The results reveal that when the tube length increases, the velocity, pressure and temperature fields tend to be fully developed. Also, the pressure drop tends to increase, but the flow drag tends to a fixed value. As the particle volume fraction increases, the average flow drag increases but the average heat transfer rate decreases. As the the external magnetic field increases, the average flow drag increases and the average heat transfer rate also increases in the general case.