噴射真空產生器因體積小且產生真空方便之特性，在搬運精密及不規則形狀之物品具有優勢，故於自動化生產之應用十分廣泛。本數值研究模擬分析二段式真空產生器之流場及性能參數，包括吸入量、消耗量、真空度以及第二段最高真空度；並執行系統化之參數分析工作，包括主噴嘴、連接管、與混合排氣管之幾何參數對其性能之影響。最後整理參數分析之結果，並據以設計出兩款優化真空產生器，其中一款是以性能為目標的優化模型，另一為符合實際性能需求之最短長度真空產生器，可使其降低成本且安置更加彈性。
經由數值計算與參數分析之結果顯示，原始二段式真空產生器之長度為55.5mm，達到真空度-90KPa之供給壓力為0.43MPa，此壓力下之吸入量為45.2L/min、能源效率為20.1%，至於真空度峰值-94.2KPa則須供給壓力0.55MPa。而本文之最小體積模型之長度僅有35.5mm，於各壓力下之性能與原始模型相近，而其能源效率為20.6%；另外，此模型在供給壓力0.45MPa即可達到真空度峰值，這表示最小體積模型在運作更節省能源，且具有方便安置與成本優勢。至於另一款性能優化模型之長度為54.5mm，此模型在各壓力下所有性能皆優於原始模型，特別是在供給壓力0.4MPa時，此優化模型就已達到真空度-90KPa，且所產生之吸入量為49.0 L/min、能源效率為24.8%，明顯地較原始真空產生器高出許多；這代表性能優化模型除具有節省能源之優勢外，還能更快地達到所需之真空度並提供更多的吸入量。綜合歸納來說，本研究建立一套系統化的設計流程，也取得各重要參數對真空產生器性能之影響，並藉此成果規劃出兩款優化模型，以滿足特定需求之二段式真空產生器的應用。

Recently, the vacuum ejector has become an essential and popular device in the automation industry because of its compact size, simple construction, and quick response feature. Thus, it is crucial to establish the design guidelines for optimizing the vacuum ejector to meet different application needs. To meet with this demand, this numerical investigation is motivated to execute the parametric study and the optimization effort on a two-stage vacuum ejector, which can generate a higher suction flowrate with a better efficiency compared to the single-stage ejector. Firstly, with the aids of CFD technology, the geometric parameters regarding the principal converging-diverging nozzle, the connecting duct between stages, and the discharge pipe, are evaluated and studied systematically to yield an in-depth understanding of the corresponding effect on the vacuum generator's performance, which is judged based on the vacuum pressure, the suction flowrate, and the energy efficiency factor. Later, outcomes of the aforementioned parametric analysis are utilized as the guidelines to propose two optimum vacuum ejectors for fulfilling the requests of the superior performance and the minimum length, respectively.
As a result, numerical calculations indicate that the reference two-stage vacuum ejector with a length of 55.5mm generates -90KPa vacuum pressure, 45.2L/min suction flowrate, and 20.1% efficiency under the 0.43 MPa pressure supply. Also, the minimum-length vacuum ejector with a length of 35.5mm (i.e., 20mm reduction) delivers almost the same performance characteristics as these of the reference model at an efficient manner (20.6% energy efficiency factor). Besides, this compact model can reach the peak vacuum pressure under the supply pressure of 0.45MPa, which is clearly lower than 0.55 MPa for the reference generator. Regaining the modified vacuum generator aiming performance enhancement, all the performance characteristics are upgraded over the operating pressure range of 0.4~0.6 MPa via the CFD predictions. Moreover, this high-performance vacuum ejector can produce -90KPa vacuum pressure, 49L/min suction flowrate, and 24.8% energy efficiency under the 0.4 MPa pressure supply. Obviously, this optimized model with the similar length of 54.5mm can operate efficiently since it delivers the required vacuum pressure at a lower pressure supply. In conclusion, the accomplishment of this research provides a systematic design scheme for constructing the optimized two-stage vacuum ejector to meet the particular requirement in engineering applications. Also, the results of parametric study can serve as a convenient design guideline for both the one-stage and the two-stage vacuum generators.

[1] 曾賢壎，陳義男，“氣壓學”，新科技書局，1990年。
[2] 陳峰志，賴添興，“正排氣真空幫浦”，科儀新知，第二十二卷，第一期，2000年8月，第52-59頁。
[3] 俊尚科技，“真空幫浦 Vacuum Pumps”，http://www.junsun.com.tw/index.php/zh/vacuum-bases-components/2018-02-26-02-29-24/vacuum-pumps.html，2018年。
[4] ASHRAE Equipment Handbook, “ Stream Jet Refrigeration Equipment, ”ASHRAE, US, pp. 13.1-13.6, 1979.
[5] J.H. Keenan and E.P. Neumann, “ A simple air Ejector, ” Journal of Applied Mechanics, Trans. ASME, Vol. 64, pp A75 – A81,1942.
[6] J.H. Keenan and E.P. Neumann, and F. Lustwerk, “ An Investigation of Ejector Design by Analysis and Experiment, ” Journal of Applied Mechanics, Trans. ASME, Vol. 17, pp. 299 – 309, 1950.
[7] J Fabri and R Siestrunck, “ Supersonic Air Ejectors, ” Advances in Applied Mechanics, Vol. V, pp. 1–34, 1958.
[8] J.M.A. Dandachi, “ Steam Air Ejector Performance and Its Dimensional Parameters,” Loughborough University of Technology, Ph.D. Dissertation, 1990.
[9] D. W. Sun and I. W. Eames, “ Recent Developments in the Design Theories and Applications of Ejectors-A Review, ” Journal of the Institute of Energy, Vol. 68, pp. 65-79, 1995.
[10] B. I. Huang, I. M. Chang, C. P. Wang, and V. A. Petrenko. “ A 1-D Analysis of Ejector Perfonnance,” International Journal of Refrigeration, Vol. 22, pp. 354-364, 1999.
[11] 鄭兆偉，“噴射器最佳化等截面段長度的設計與分析”，國立台灣大學碩士論文，2011年。
[12] Y. Bartosiewicz, Z. Aidoun. P. Desevaux, and Y. Mercadier, “ Numerical and Experimental Investigations on Supersonic Ejectors, ” International Journal of Heat and Fluid Flow, Vol. 26, pp. 56-70, 2005.
[13] Teng Yan, Xiaoning Li, Jianping Lu, and Zhongsheng Sun, “ Research on New Energy-Saving Vacuum Ejector with Flow Self-Regulation, ” Proceedings of the 7th JFPS International Symposium on Fluid Power, pp. 759-764, September 15-18, 2008.
[14] Xiaobin Pan and Xiaoning Li, “ Research on Energy-Saving Control of Piston Typed Pneumatic Vacuum Generator,” Proceedings of the 7th JFPS International Symposium on Fluid Power, pp. 461-464, September 15-18, 2008.
[15] C, Liao,“ Gas Ejector Modeling for Design and Analysis, ” Ph.D. Dissertation, Texas A & M University, College Station, TX, 2008.
[16] Gutti Rajeswara Rao, U.S. Ramakanth, and A. Lakshman, “ Flow Analysis in a Convergent-Divergent Nozzle Using CFD,” International Journal of Research in Mechanical Engineering, Volume 1, Issue 2, pp. 136-144, October-December, 2013.
[17] 林郁民，“三口二位電磁閥之流場模擬分析”，國立台灣科技大學機械工程學系碩士論文，2017年。
[18] 陳凱鑫，“二段式真空產生器之數值模擬與性能提升分析”，國立台灣科技大學機械工程學系碩士論文，2020年。
[19] 陳毅，“一段式真空產生器之模擬分析與性能優化”，國立台灣科技大學機械工程學系碩士論文，2021年。
[20] 台灣氣立股份有限公司，“真空產生器產品型錄”，台灣氣立股份有限公司官方網站，2020年。
[21] SMC(中國)有限公司，“現代食用氣動技術”，第2版，北京，機械工業出版社，2004年。
[22] 滕燕，“新型流量自調式節能真空發生器的研究”，南京理工大學，機械製造及其自動化博士論文，2007年。
[23] 陳發林，“空液壓控制的分析與設計”，全華科技圖書股份有限公司，1985年。
[24] 呂淮熏，黃勝銘，郭興家，“氣液壓學”，高立圖書有限公司，2015年。
[25] James E.A. John, “ Gas Dynamics, ” 2nd Edition, Allyn and Bacon, Inc., 1987.
[26] E. Launder and D. B. Spalding, “ Lectures in Mathematical Models of Turbulence, ” Academic Press, London, England, 1972.
[27] D. C. Wilcox, “ Formulation of the K-Omega Turbulence Model Revisited, ” AIAA Journal, Vol. 46, No. 11, pp. 2823-2838, 2008.
[28] F. R. Menter, “ Two-Equation Eddy-Viscosity Turbulence Models for Engineering Applications, ” AIAA Journal, Vol. 32, No. 8, pp. 1598-1605, August 1994.
[29] F. R. Menter, “ Zonal Two-Equation k-ω Tubulence Models for Aerodynamic Flows, ” AIAA-93-2906, 1993.
[30] B.E. Launder and D.B. Spalding,“ The Numerical Computer of Turbulent Flow, ”Computer Methods in Applied Mechanics and Engineering, Vol. 3, No. 2, pp. 269-289, 1974.
[31] W. Shyy, S.S Thakur, H. Ouyang, J. Liu and E. Blosch, “ Computational Techniques for Complex Transport Phenomena, ” Cambridge University Press, 2005.