渦輪分子幫浦抽氣機構之研究

Abstract

本文擬採用Antoniou等人所提出之拖曳法(drag method)來預測複合式渦輪分子幫浦的性能。文中對抽氣速率和壓縮比隨幫浦幾何參數之變化作一數值模擬，其包含葉片或螺旋凹槽通道之平均半徑、傾斜角度、前端厚度、單層碟片之葉片數或螺旋凹槽通道數和葉片長度等，並與前人所得之實驗數據做比較，最後則以兩家公司之TMP的實驗數據來驗證並調整性能預估公式。本文亦對複合式渦輪分子幫浦(Compound TurboMolecular Pump)有一詳細地介紹，包括有整個系統架構的說明、幫浦性能預測理論之數學模型的推導、幫浦性能曲線的量測及測試系統的建立等，文末則規劃出一個渦輪分子幫浦的設計製造流程，包含有轉子葉型之設計、零件繪製加工與幫浦之性能測試。 由本文的研究成果發現，複合式渦輪分子幫浦的轉子設計，在靠近進氣口處採用多級式渦輪葉片的設計，而在靠近排氣口處採用螺旋溝形轉子的設計。在多級式渦輪分子幫浦葉片的設計上，在靠近幫浦進氣口處宜採用高抽氣速率的設計，而在靠近螺旋溝形轉子處宜採用高壓縮比之設計。在數學模式方面，與其他單級式渦輪葉片的文獻結果相比較發現，當葉片的傾斜角度在20□~30□及葉片切線速度與分子熱速度比值為1時，Antoniou的模擬結果和其他人的實驗及數值模擬較為相近。將有效抽氣速率的公式與Antoniou單級式性能預測公式相結合可得到整顆複合式渦輪分子幫浦的性能模擬的數學模式。將兩家公司的複合式渦輪分子幫浦的相關設計代入性能模擬的數學模式並與實驗量測結果相比較發現，預測所得的抽氣速率和壓縮比比實驗值高約20% 左右，顯示本論文所發展的複合式渦輪分子幫浦性能預測模式有相當的準確性。當理論模擬計算公式以單級之渦輪分子幫浦的尺寸為基準時，在葉片的設計上，幫浦進氣口處可採取較少葉片數、葉片前端厚度較小、葉片傾斜角度介於為30□~40□之設計，以得到較高之抽氣速率；在靠近螺旋凹槽式轉子處則採較多葉片數、葉片前端厚度較大、葉片傾斜角度介於18□~28□之設計，以得到較高之壓縮比，且在葉片切線速度與分子熱速度比值小於1的情況下，轉子轉速、平均半徑與葉片的長度則是越大越好。在螺旋凹槽轉子的設計上，靠近葉片式轉子處採螺旋凹槽通道之傾斜角度介於35□~45□間、螺旋凹槽數較少、螺旋凹槽深度較大與凸起葉輪厚度較小之設計，以得到較高之抽氣速率；在靠近幫浦排氣口處則採螺旋凹槽通道之傾斜角度介於25□~35□、螺旋凹槽數較少、螺旋凹槽深度10~12 mm與凸起葉輪厚度介於 8~12 mm，以得到較高之壓縮比。就渦輪葉片及螺旋凹槽的性能預測而言，當轉子之轉速及轉子之平均半徑越大則幫浦之性能當然是越好。

In this thesis, the Antoniou’s drag method is adopted to predict the performance of compound Turbo Molecular Pump (TMP). The numerical models of pumping speed and compression ratio are functions of the geometrical parameters of the pump including blades’ or helical grooves’ mean radius, inclined angles, front widths, number of blades in each disc or of helical grooves and the length of blades. The results of numerical simulation for one single pumping stage are compared and verified with the articles proposed before. The model of predicting total pumping speed and compression ratio for compound TMP is modified due to experimental results of two company’s compound TMP. The system of compound TMP is described in detail in this thesis including the mathematical model of the performance predicting theory, measurement procedure of the pumping performance and facility of pumping performance test. At the end of this thesis, the procedure of designing TMP is described including the design of rotor shape, CAD/CAM and the pumping performance test of the new pump. From the result of this research, the pump will have a better performance if the multi-stage blades are put near the entrance and the helical grooves near the exhaust of the compound TMP. For designing the multi-stage blades of TMP, it will get a better pumping performance by the following rules : put the high pumping speed design of blade structure at the entrance of the compound TMP and a higher compression ratio design at the region near the helical-groove rotor. Comparing with the experimental and numerical simulation results published before for the single-stage blade rotor shows that the Antoniou’s model agrees well with others’ work when the inclined angle is between 20~30□ as the ratio of blade’s tangent speed and molecule’s thermal velocity is around 1. In order to get the total pumping speed of compound TMP, the effective pumping speed equation is adopted to link with Antoniou’s single-stage pumping equations. The comparison of numerical results and experimental measurements of two company’s TMP shows that the predicting pumping speed and compression ratio is higher about 20□ than experiments. It shows the numerical model used in this study is accurate at usefulness. So, the rules to design the shape of rotor for compound TMP are follows : (1) For turbo blade structure : small blade numbers, small blade thickness and inclined angle between 30□ and 40□ could be arranged in the region near the entrance of TMP to get higher pumping speed. For the region near the helical groove rotor, large blade numbers, large blade thickness and inclined angle between 18~28□ would be better to get the higher compression ratio. (2) For helical groove structure : the inclined angle between 35~45□, small groove numbers and small groove thickness could be arranged in the region near the turbo blades rotor to get higher pumping speed. For the region near the exhaust of TMP, the inclined angle between 25□ and 35□, small groove numbers and groove thickness between 8 to 12 mm would be better to get higher compression ratio. (3) For both turbo blade structure and helical groove rotor, the pumping performance will be increased when the rotating speed and averaged radius of rotor are increased.