雷射投影機與傳統光源顯示相比，具有高亮度、高穩定性且壽命長等特點，可以使投射出之影像真實重現，提供出更具震撼的視覺效果，因此成為目前最受重視之投影機產品。通常投影機採用出入風口右進左出之強制對流散熱為設計準則，但此規劃容易吸入灰塵雜質導致光學機構故障；同時當機器安置較接近觀眾，則所排出之熱空氣會有傷人之可能，另外冷卻扇運轉所產生的噪音影響使用品質，這些都是有待解決之挑戰。有鑑於此，本研究針對雷射投影機進行散熱規劃及減噪設計，結合數值模擬及實測工具來驗證其成效與可行性，以建立一套系統化的投影機設計模式。在系統散熱設計部份，以下進下出之出入風口及發熱功率規格之最大化為目標，首先檢視原始投影機設計之發熱元件及熱流場狀況，再藉由數值模擬工具來檢驗，本文提出之主熱源隔絕、管道散熱模組及放射狀鰭片等各項散熱方案；分析結果顯示，結合上述散熱規劃與改善後，成功地在較低之機身開孔率下，即能令投影機系統操作於較高功率下(由92.2W提升至150W)，同時使發光元件之溫度皆能於安全範圍內。
最後製作出可量產之系統散熱模組的實體模型，以供進行優化投影機之散熱性能測試，由模擬及實驗結果之比較顯示，各監測點溫度差異值落在1.2~2.4℃，充分地驗證本研究數值模擬之準確性，以及所設計的散熱模組於實際應用之可信性。在系統減噪設計部分，先透過噪音實測分析投影機系統及軸流冷卻扇之聲壓與頻譜特性，在掌握投影機主要噪音源為軸流扇後，應用其頻譜特性設計出合適之亥姆霍茲共振器；同時透過軸流扇之聲壓擾動變化的數值分析發現，在外框靠入口處之擾動變化最明顯，故設計製造並安裝各式之亥姆霍茲共振器於此位置，所考量之共振器參數有不同尺寸及裝配型式。經過配置共振器之風扇的噪音實測後，確認除了軸流風扇單體之特徵頻噪音獲得改善外，整體噪音值也同時降低
4.8 dBA。最後，本研究將最適化之共振器配置於投影機系統中進行測試，實驗數據顯示這項降噪設計之效果優異，除了令特徵頻噪音降低外，也使雷射投影機之整體噪音降低2.5 dBA。

The goals of this research are focused on thermal management and
noise reduction of the next-generation laser projector, which is capable to
deliver the high-quality video output with an extreme brightness. At first,
a sample projector is selected from the available commercial products to
perform CFD simulation and experimental measurement for validating the
numerical model established here. Also, the calculated flow patterns and
temperature distributions are visualized and used to generate ideas for
upgrading its thermal-management capability. Moreover, the ventilating
holes for both inlet and outlet airstreams are rearranged to locate on the
bottom surface of projector case so as to prevent the possible accident
causing by the exhausted hot air and to minimize the inhaled dust, which
is considered as the main reason for triggering the electronic failure.
Thereafter, various thermal-design concepts, such as the isolation of
major heat-dissipating source, the duct-like arrangement on thermal
module, and the heat sink with radiative fins, are included to generate three
heat-dissipating alternatives, which are evaluated systematically with the
aids of the commercial CFD software Fluent. Noteworthily, all proposed
thermal designs incorporated with laser projector are analyzed under both
the ceiling installation and the desktop operation, which is the worst
environment for thermal-dissipation consideration. Consequently, an
improved thermal design is attained and verified numerically to maintain
the operating temperatures of major electronic components under their safe
limits while the power consumption of laser projector is increased from 92W to150W in the critical desktop situation. Afterward, in accordance
with the mass-production and the cost considerations, a realistic revision
of the modified thermal module is fabricated with CNC and 3D-printing
technologies to execute the corresponding thermal and acoustic
performance experiments. As a result, the well correlated trends with
deviation ranging from 1.2 to 2.4 ℃ are observed for temperature
comparisons between the on-board test and the numerical calculation over
main components inside this laser projector.
With regard to the noise-reduction effort, the acoustic fields associated
with the cooling fan and the projector system are calculated successively
and analyzed carefully via the transient CFD simulation, then FFT analyzer
is applied to measure their noise characteristics inside a semi-anechoic
chamber. Subsequently, a thorough understanding on the acoustic features
of this cooling fan is achieved and utilized to design several Helmholtz
resonators, which are manufactured and installed on the inlet side of fan
frame and the projector system later for evaluating the associated noisereduction
outcomes via both CFD and experimental techniques. It is found
that the trend and deviation between CFD and test results are well
correlated and within an acceptable range. In summary, according to the
experimental results, the maximum noise reduction is observed as high as
14.4 dBA on its 2nd harmonic frequency while the overall sound pressure
level is recorded a 2.5 dBA reduction for the laser projector equipped with
10 proper Helmholtz resonators. In conclusion, the accomplishment of this
study provides a systematic design scheme for the thermal management
and the noise reduction of the video projector with the implement of Helmholtz resonator installed on its cooling fans.

[1]明基電通網站雷射投影機色度圖
http://www.benq.com.cn/prj/lx810std/

[2]LCD投影技術介紹
http://www.3lcd.com/tw/explore/default.aspx

[3]DLP投影技術介紹
http://www.ti.com.tw/articles/detail.asp?sno=18

[4]LCOS投影技術介紹
https://www.ctimes.com.tw/DispArt/tw/PBS/color-sequential/DLP/HTPS/Rainbow-Effect/0908041211WW.shtml

[5]呂紹旭，”微型投影機發展現況”，光電科技工業協進會，2010年。

[6]Turner, M. and Rotron, C., “All You Need to Know about Fans,” ,Electronics Cooling, January 2000.

[7]Wang, D. G., “Optimization of System Fan Placement,” Proceeding of the 2000 IEMT/IMC Thermal Management, April 2000.

[8]Chapman, C. L., Lee, S., and Schmidt, B. L., “Thermal Performance of an Elliptical Pin Fin Heat Sink,” Tenth IEEE Semi-Therm, pp. 24-31, 1994.

[9]Lau, K. S. and Mahajan, R. L., “Effects of Tip Clearance and Fin Density on the Performance of Heat Sinks for VLSI Packages,” IEEE Transactions on Components, Hybrids, and Manufacturing Technology, Vol. 12, No. 4, pp.757-765, 1998.

[10]鄭憶湘，”散熱片在強制對流下之最佳化設計與實驗”，國立清華大學工程與系統科學研究所碩士論文，2002年。

[11]陳煒杰，” 數值模擬運用結構法則來強化太陽花散熱鰭片效能”， 淡江大學航空太空工程學系碩士論文，2015年。

[12]黎俊和，”液晶投影機的發展介紹與對數位光源處理投影機之光機研究”，國立交通大學機械工程研究所碩士論文，2003年。

[13]陳柏安，”DLP液晶投影機之熱流場數值分析”，國立台灣科技大學機械工程研究所碩士論文，2004年。

[14]張志賢，”投影機之散熱分析與對策”，國立清華大學工程與系統科學研究所碩士論文，2006年。

[15]陳文揚，”液晶投影機控制參數對關鍵組件之影響研究”，國立台灣海洋大學機械與機電工程研究所碩士論文，2007年。

[16]劉桓志，” LED微型投影機的散熱設計之模擬與實驗整合研究”，國立台灣科技大學機械工程研究所碩士論文，2011年。

[17]Zeller, W. and Stang, H., “Predetermination of the Axial-Flow Fans,” Heizung-Luftung-Haustchnik, Vol. 9, No. 12, pp. 345–357, 1957.

[18]Zeller, W., “Conerning Mathematical Treatment of Noise Behaviour in Fans for Air Conditioning Plants,” VID-Berichte, No. 38, 1959.

[19]Hüebner, G., “Noise Generated by Centrifugal Fans,” Siemens-Zeitschrift, Vol. 8, pp. 145-155, 1959.

[20]Schlichting, H., “Application of the Boundary Layer Theory to Flow Problems of Turbo Machines,” Siemens-Zeitschrift, Vol. 33, No. 7, pp. 74-82, 1959.

[21]Neise, W., “Noise Reduction in Centrifugal Fans: a Literature Survey,” Journal of Sound and Viberation, Vol. 45, No. 3, pp. 375-403,1976.

[22]Neise, W. and Koopman, G. H., “Reduction of Centrifugal Fan Noise by Use of Resonator,” Journal of Sound and Viberation, Vol. 72, No. 2, pp. 297-308, 1980.

[23]吳御銓，” 1/4λ減噪器應用在離心扇之數值與實務整合研究”，國立台灣科技大學碩士論文，2014年。

[24]Alster, M., “Improved Calculation of Resonant Frequencies of Helmhlotz Resonantors,” Journal of Sound and Vibration, Vol. 24, No. 1, pp. 63-5, 1972.

[25]Parente, C. A., “Hybird Active/Passive Jet Engine Noise Suppression Systems,” NASA CR-1999-208875, NSL-RPT-98-002, February, 1999.

[26]Han, S. H., “Sound Reduction by a Helmholtz Resonator,” Master Thesis, Lehigh University, 2008.

[27]Han, S. S. and Rhim, Y. C., “Noise-Level Reduction of a Slim-Type Optical Disk Drive Using the Idea of a Helmholtz Resonator,” Transactions on Magnetics, Vol. 45, No. 5 , pp. 2217-2220, 2009.

[28]陳彥彰，” 亥姆霍茲共振器應用於管路風機之實驗與模擬整合研究”，國立台灣科技大學碩士論文，2014年。

[29]Cai, C. Z., “An Extended Neck versus a Spiral Neck of the
Helmholtz Resonator,” Master Thesis, Department of Building Services
Engineering, The Hong Kong Polytechnic University, 2016.

[30]Zhao, X. D., “Improving Low-Frequency Sound Absorption of
Micro-Perforated Panel Absorbers by Using Mechanical Impedance
Plate Combined with Helmholtz Resonators,” Master Thesis, School
of Automobile and Traffic Engineering, Jiangsu University, 2016.

[31]Lienhard, J. H., “A Heat Transfer Textbook,” 3rd Ed., Cambridge,
Massachusetts, U.S.A., 2001.

[32]Latham, C. A., “Thermal Resistance of Interface Materials as a
Function of Pressure,” Electronics-Cooling, Vol. 2, No. 2, pp. 35,
1996.

[33]Lee, S., “Calculating Spreading Resistance in Heat Sinks,”
Electronics-Cooling, Vol. 4, No. 1, pp. 30-33, 1998.

[34]Wikipedia, http://en.wikipedia.org/wiki/Helmholtz_resonance

[35]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.

[36]Launder, B. E. and Spalding, D. B., “Lectures in Mathematical Models of Turbulence,” Academic Press, London, England, 1972.

[37]Modest, M. F., “Radiative Heat Transfer,” McGraw Hill, 1993.