利用葉片式渦流產生器之熱傳增強

Abstract

本論文是以數值方法研究在圓管流內入葉片式渦流產生器的流場 與熱傳增強效果。統禦方程式轉換至非正交曲線座標上，利用有限體 積積分法將方程式離散化，壓力之離散化採用相鄰19點相關格點求解， 計算格點則使用非交錯式綱格佈置，再以SIMPLE法則求解代數方程式。 研究範圍包括：一.雷諾數為以2000基準，Prandtl numbre為5，內置 各种不同型式渦流產生器之光滑管流場及熱傳分析；二.在上述圓管 內附加不同長度鰭片，分析其熱傳增強效果；三.對光滑管之紊流流 場進行數值分析。 葉片式渦流產生器可以誘導出次級速度，並在葉片出口後短距離 內形成軸向渦流，軸向渦流可以導致熱傳的增強，然而壁面的磨擦及 壓降的損失亦增大。增加葉片之軸向斜率對於熱傳的增強有很大的幫 助，例如增加葉片的高度、減少葉片的軸向長度及使用向內凹的葉片 形狀皆可增加熱傳，此外，葉片數採用五或六片的渦流產生器有較佳 的性能。對於A型葉片式渦流產生器圓管流，增加鰭片有助於熱傳增強， 且鰭片的長度越大，熱傳量越大。對於A型葉片式渦流產生器完成雷 諾數2×105紊流範圍之流場與熱傳數值分析。其熱傳量、環流量及摩 擦係數皆較層流者大為增加。

The flow and heat transfer in a tube with multilobe vortex generators inserted are studied using numerical method. The governing equations are transferred to curvilinear coordinates to fit the irregular geometry. Discretization is made by using the finite-volume integral method with non-staggered grid arrangement. The pressure-correction equation is solved over 19 neighboring points. The system of algebra equations are solved by the SIMPLE-type algorithm. Categories of the thesis have three departments: 1. Analysis a tube flow by putting multilobe vortex generator in it. The Reynolds number is mainly fixed at 2000 and the Prandtl number is 5. 2: inside the wall of the above-mentioned tube, we added different length of fins, to analysis the heat enhancement 3: Analysis of the turbulent flow of the smooth tube. When fluid flows through the vortex generator, secondary velocities are induced and axial vortices are formed after a short distance downstream of the exist of the lobe. The axial vortices leads to enhancement of heat transfer as well as friction and pressure loss.. Heat transfer can be improved by increasing the axial slope of the lobe through increasing the lobe penetration, reducing the lobe length, and making a concave lobe shape. Five or six lobes for the vortex generator are sufficient to y ield good performance. The heat transfer can be improved by increasing the length of fins. A three-dimensional flow calculation procedure has been successfully incorporated to study the turbulent flow for Reynolds number is 2×105. It's heat transfer, circulation and friction coefficient is much larger than laminar flow.