螺旋凹槽式分子邦浦之流場分析

Abstract

本文是計算流體力學的方法分析螺旋凹槽式分子邦浦內的流場。為處理直角交錯網格不易解決的不規則邊界，本研究採用非正交曲經座標，計算格點則使用非交錯式網格佈置，以SIMPLE法則求解代數方程式。研究範圍包括：一、以三種不同流道安排及滑動與非滑動邊界條件分析Urano與Enosawa的實驗案例；二、將上述三種流道計算所得的結果與實驗值比較之；三、探討各設計參數對邦浦抽氣效能的影響。 由計算結果可看出，流道外型最為簡化的A流道，其結果與其他兩種接近實際形狀的流道之結果非常接近。以滑動邊界條件計算所得的結果，其進出口的壓力差與實驗結果相比有些微改善。由所測試的幾種流量可看出在低流量時出口處的壓力高於進口處的壓力，此逆向壓力梯度導致在靠近出口處產生迴流。本研究的另一貢獻是以動量平衡的理論分析各參數對邦浦的影響，根據此理論，壓力的提升主要是由流道兩側邊的壓力差所造成。選取作為測試的幾何參數有：流道與水平之間夾角、流道數目、流道高度及流道置於轉子與靜子的差別。結果顯示流道與水平的夾角及流道高度存在一最佳值可得到較佳的抽氣效能：流道數目較少時造成入口處的壓力較低，因而有較好的效能；將流道置於轉子上時移動壁面的速度較將流道置於靜子上時快，所得之結果較佳。

A computaional procedure is described to analyze the flow in the helical grooves of a molecular pump. To fit the irregular boundaries of the flow field curvilinear non-orthogonal coordinates are employed. The system of algebraic equations are solved by the SIMPLE-type algorithm. The work done in this researth is divided into three categories: 1. Use three different groove arrangements along with slip and no slip boundary conditions to analyze the flow in a molecular pump investigated experimentally by Urano and Enosawa. 2. Compare the computational results and experimental data. 3. Analyze the effects of geometric parameters. It can be seen from the calculations that th use of a simplified groove model, termed type A, can yield close results to the other more realestic groove models. With the slip boundary condition, the pressure difference between inlet and exit is improved, though not significantly, leading to closer agreement with experiments. A number of flow rates are tested. It is shown that at low flow rates the pressure at exit is higher than that at inlet. Due to the adverse pressure gradients, recirculating flow is formed in the downstream region near th exit. Another important contribution of this research is the use of a momentum balance theory to analyze the effects of geometric parameters. According to the theory, the pressure promoted by the pump is caused by the pressure difference exerted on the two side walls of the groove. The geometric parameters chosedn to test are: groove angle, groove numbers, groove height and either setting of the grooves on the rotor or stator. The results show that there exist an optimum groove angle and an optimum groove height to obtain best pumping effectiveness. The tests also show that with less number of grooves leads to lower inlet pressure and, thus, higher performance. The setting of grooves on the rotor is prefered to that on the stator because the former gives higher moving wall speed and better pumping performance.