本文針對潔淨室送風系統之FFU(Fan Filter Unit)進行改良，使其具備高性能、效率及出風高均勻度等要求，為加速改良進度和減少原型製作成本，先藉由發展成熟的數值CFD軟體Fluent，就FFU之原始設計進行流場模擬；並將計算結果製作各式圖表，以供進行細部流場可視化，經由仔細觀察分析判定流場缺失的位置與產生原因，接著根據流場缺失提出改善方案。歸納分析後判斷，有效之改善參數包括葉片護罩、入口圓錐體、葉輪中心體、NACA翼形葉片、內部流道及出口等部分；同時模擬結果顯示經採用部分參數改善後，在相同轉速1,240 RPM、操作點(270 mmAq)情況下，優化FFU方案之性能與原型 FFU 流量(1,039CFM)相比，其流量有 302 CFM (29%)的巨幅增加，而靜壓效率更從 65.6 ％增加至 73.8%。另外出口正向流出區域的面積比例提升至57.66 ％，比起原型 FFU 的 45.03 ％要高出許多，而原本在出口兩側產生局部高風速現象也獲得改善，這對於過濾器使用壽命的延長以及 FFU 出風均勻度的提高都有很大幫助，整體來看改良之後其各方面的表現都比原型 FFU 風機要來得優異許多。
在噪音方面，研究過程分別使用針對第一及第二特徵頻所設計之共振器，其中探討不同數量對於FFU風機之減噪效果，以及簡諧共振對於其它特徵頻之影響，發現共振器對於特徵頻有明顯的減噪效果；使用第一特徵頻共振器時，令FFU的第一特徵頻降了3~6dBA，在第二特徵頻有2~5 dBA的減噪效果，更在第三、四特徵頻的減噪效果高達10~12 dBA。而使用第二特徵頻共振器時，使FFU風機的第二特徵頻降了5~9 dBA，而其倍頻之第四特徵頻也有5~10 dBA的效果；但其對非倍頻之特徵頻(第一及第三特徵頻)的效果較差，不過仍舊有1~3 dBA 的效果。在共振器之裝設數量上，發現使用5個共振器比3個共振器之表現較佳，以使用第一特徵頻共振器為例，在前四個特徵頻的降噪效果都比3個共振器的案例要多出3~6 dBA。綜觀上述結果得知，本研究之完成可在FFU的設計與開發上，建立具有一套系統化與科學性之分析流程，能提供可信賴的完整分析結果，作為將來生產時的建議及參考依據，且對於提昇FFU整體性能將有所助益。

Nowadays, fan filter unit (FFU) with high-efficiency and low-noise characteristics is in great demand for minimizing the operation costs of the clean room. This demand motivates this numerical investigation to improve flow pattern inside FFU for enhancing its static-pressure efficiency, aerodynamic performance, and the uniform distribution at the discharge. Additionally, Helmholtz resonator is implemented to FFU for reducing the SPL (sound pressure level) of the annoying narrow-band noise. At first, a commercial FFU is chosen to calculate numerically its aerodynamic performances for serving as the comparing base in the framework of CFD code Fluent. The CFD outcomes are in agreement with the experimental results over the entire performance curve. Also, this FFU generates 1,039 CFM with a 65.6% static-pressure efficiency under operation point (270 mmAq) at 1,240 rpm. Later, the computed flow field is analyzed for creating alternatives of further improvement. It follows that the above analysis identifies some important design parameters, such as area and contour of FFT inlet, blade number and airfoil shape of rotor design, FFU casing geometry, and guiding arrangement inside FFU configuration. Consequently, the combination of these optimized parameters are employed to construct the optimum FFU, which is estimated to produce flowrate, static-pressure efficiency, and flow uniformity at FFU outlet as 1,341 CFM, 73.8%, and 57.7% under the operating condition. These performance outcomes represent 29.1% flowrate enhancement and 8.2% efficiency increase. Moreover, an apparent improvement on uniform distribution is well demonstrated by increasing the effective area ratio at FFU outlet from 45.0% to 57.7%, which results in a longer life for the filter.
With respect to the noise analysis, transient CFD simulation of the optimum FFU is executed to generate the acoustic spectrum, which illustrates the harmonic frequencies and the proper locations for resonator application. Thereafter, two Helmholtz resonators aiming at the first two harmonic frequencies are designed and installed onto the improved FFU for reducing the annoying harmonic noise. According to the corresponding CFD simulations, the installation of 5 resonators aiming at the 1st harmonics yields the impressive noise reductions as 6.4 dBA and 5.5 dBA for the first two harmonic frequencies. Also, installation of 5 resonators targeting the 2nd harmonic results in the highest noise reduction (9.9 dBA) on the 2nd harmonic frequency while a minor decrease (2.8 dBA) is observed at the fundamental harmonic frequency. Evidently, the noise-reduction effect is well demonstrated by introducing Helmholtz resonators incorporated with FFU system. In conclusion, this study establishes a systematic and reliable scheme for the performance enhancement and the noise reduction of FFU system via a comprehensive CFD investigation.

參考文獻
[1] Whyte, W., “Cleanroom Design”, Second Edition, John Wiley ＆Sons Ltd, Chichester, October 1999.
[2] 胡石政、蔡尤溪、黃賢強，“Axial Fan與FFU系統潔淨室性能之分析比較”，電子月刊，pp. 121-128，民國89年12月。
[3] Okuma, T., “Energy-saving Design for Air-conditioning Systems in Semiconductor Clean Rooms”, Clean Technology, January, 1997.
[4] 胡石政、李昇榮、林瑋義、詹皇烈，“無塵室用FFU之出風氣流性能量測與分析”，冷凍與空調，pp. 117-125，民國90年6月。
[5] 蕭宗容、胡石政、涂茂齡，“風機濾網機組(FFU)的氣流特性研究”，冷凍與空調，pp. 84-91，民國91年2月。
[6] 李延青、鄭名山、陳來富、李隆正，“4’×4’ FFU開發-3D流線導葉片擴散器之應用”，中華民國機械工程學會第二十屆全國學術研討會論文集，台北，pp. 1381-1388，中華民國92年。
[7] 李延青、鄭名山、李隆正，“4’×4’ FFU開發-3D流線導葉片擴散器之設計參數模擬分析”，冷凍與空調，pp. 65-73，民國94年4月。

[8] 謝旻翰，“風機濾網機組之流場數值分析”， 國立台灣科技大學機械工程技術研究所碩士論文，民國97年。
[9] Moller, P. S., “A Radial Diffuser Using Incompressible Flow between Narrowly Speed Disk”, Journal of Basic Engineering, pp. 155-162, 1966.
[10] Gardow, E. B., “On the Relationship Between Impeller Exit Velocity Distribution and Blade Channel Flow in a Centrifugal Fan”, Ph.D. Thesis, Feb., 1968, State University of New York at Buffalo.
[11] Leidel, W., “Einfluss Von Zungenabstand and Zungenradius auf Kennlinie und Gerausch eines Radial Ventilators ”, DLR-FB, 61-69, 1969.
[12] Hussain, A. K., and Ramjee, V., “Effects of the Axisymmetric Contraction Shape on Incompressible Turbulent Flow”, ASME Journal of Fluids Engineering, pp. 58-69, 1976.
[13] Raj, D. and Swim, W. B., “Measurements of the Mean Flow Velocity and Velocity Fluctuations at the Exit of a F-C Centrifugal Fan Rotor”, Journal of Engineering for Power, Vol. 103, pp. 393-399, 1981.
[14] Lin, S. C., “A Novel F-C Centrifugal Fan Design for Improved Performance”, Department of Mechanical Engineering Technical Report, Tennessee Technological University, 1982.
[15] Wright, T., “Centrifugal Fan Performance with Inlet Clearance”, Journal of Engineering for Gas Turbines and Power, Vol. 106, pp.906-912, 1984.
[16] Fox, R. W. and McDonald, A.T., Introduction to Fluid Mechanics, 2nd ed., John Wiley and Sons, New York, pp.207, 1978.
[17] Kondo, L. and Aoki, Y., “Noise Reduction in Turbo Fans for Air Conditioners”, Technical Review-Mitsubishi Heavy Industries, Vol. 26, No. 3, pp. 173-179, 1989
[18] Ken, Morinushi, “The Influence of Geometric Parameters on F-C Centrifugal Fan Noise”, Journal of Vibration, Acoustic, Stress, and Reliability in Design, Vol. 109, pp. 227-234, 1987.
[19] Kjork, A. and Lofdahl, L., “Hot-Wire Measurements Inside a Centrifugal Fan Impeller”, Journal of Fluids Engineering, Vol. 111, pp.363-368, 1989.
[20] Dick, E. and Belkacemi, M., “Optimum Design of Centrifugal Fans and Pumps”, European Journal, Vol. 37, pp.9-18, 1991
[21] 吳慶財，“前傾式離心風扇之實驗設計”，國立台灣工業技術學院機械工程技術研究所碩士論文，民國82年。
[22] 吳振輝，“小型後傾式離心扇之設計”， 國立台灣工業技術學院機械工程技術研究所碩士論文，民國83年。
[23] Eck, I. B., “Fans：Design and Operations of Centrifugal, Axial-Flow and Cross-Flow Fans”, Pergamon Press, New York, 1973.
[24] Huang, J. D., Yin, M., Deng, Q., and Yao, X. J., “Effects of Concealed Motor’s Shape on the Performance of Forward Multi-Blade Centrifugal Fans”, Journal of Shanghai Jiaotong University, Vol. 35, No. 8, pp. 1196-1199, 2001.
[25] 孫鈞瑋，“前傾式離心風機數值與實驗之整合研究”， 國立台灣科技大學機械工程技術研究所碩士論文，民國93年。
[26] 黃博全、黃仁智、李岳松，“入口錐對後傾式離心風機性能影響之探討”，第十四屆全國計算流體力學學術研討會，南投縣，中華民國96年8月。
[27] Hüebner, G., “Noise Generated by Centrifugal Fans”, Siemens- Zeitschrift, Vol. 8, pp. 145-155, 1959.
[28] Smith, W. A., “Reducing Blade Passage Noise in Centrifugal Fans”, American Society of Heating, Refrigerating and Air-Conditioning Engineers Transactions Part II, Vol. 80, pp. 45-51, 1974
[29] Neise, W., “Noise Reduction in Centrifugal Fans：a Literature Survey”, Journal of Sound and Vibration, Vol. 45, No. 3, pp. 375-403, 1976.
[30] Neise, W., “Review of Noise Reduction Methods for Centrifugal Fans”, Journal of Engineering for Industry, Vol. 104, pp. 151-161, 1982.
[31] Kondo, L. and Aoki, Y., “Noise Reduction in Turbo Fans for Air Conditioners”, Technical Review-Mitsubishi Heavy Industries, Vol. 26, No. 3, pp. 173-179, 1989.
[32] Ken, Morinushi., “The Influence of Geometric Parameters on F. C. Centrifugal Fan Noise”, Journal of Vibration, Acoustic, Stress, and Reliability in Design, Vol. 109, pp. 227-234, 1987.
[33] Ken Morinushi., “Noise Source of a Multiblade Fan”, Nippon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan, Vol.57, No. 543, pp. 3837-3844, 1991.
[34] 李炫秉，“聲強法在離心扇噪音診斷與控制之研究”，國立台灣工業技術學院機械工程技術研究所碩士論文，民國84年。
[35] 洪宗揚，“後傾式離心風機之噪音研究”，國立台灣工業技術學院機械工程技術研究所碩士論文，民國85年。
[36] 呂水煙，“前傾式離心風機之減噪研究”，國立台灣工業技術學院機械工程技術研究所碩士論文，民國86年。
[37] Su, M. M., Gu, C. A., and Miao, Y. M., “Numerical Study of Viscous Flow Field in Mixed-Flow Fan”, Journal of Xi’an Jiaotong University, Vol. 30, No. 10, pp. 55-63, 1996.
[38] Patankar, S. V., and Spalding, D. B., “A Calculation Procedure for Heat Mass and Momentum Transfer in Three-Dimensional Parabolic Flows”, International Journal of Heat Mass Transfer, Vol. 15, pp. 1787-1806, 1972.
[39] 黃家烈、簡宏斌“軸流風扇之數值模擬與實驗分析”1999中華民國「航太學會/燃燒學會/民航學會」航太聯合會議，桃園，pp.107-117，中華民國88年。
[40] 黃家烈、許豐麟，“進風口面積在新式筆記型電腦冷卻扇之研究”，中華民國機械工程學會第十七屆全國學術研討會論文集，高雄，pp. 621-628，中華民國89年。
[41] 黃家烈，“筆記型電腦散熱風扇之研究”， 國立台灣科技大學機械工程技術研究所博士論文，民國90年。
[42] 張正儒
[43] Bleier, Frank P., “Fan Handbook, Selection, Application, and Design”, McGraw Hill, 1997.
[44] 李文錦，“半導體廠房潔淨室的節能空調設計之探討”，中國冷凍空調雜誌，pp. 61-69，1997年12月。
[45] 蔡永隆，“風機濾網機組性能之數值與實驗研究” ， 國立台灣科技大學機械工程技術研究所碩士論文，民國97年。