本文設計一款高性能之混流器應用於燃氣爐具，首先考量混流器應用場域及尺寸限制規劃出初始模型，接著根據操作火力需求與燃料種類，於CFD架構探討三種燃氣孔徑(3、4.2及5 mm)與兩種燃料(LPG與NG)的混流器性能；分別審視相關之內部氣體混合、速度分佈與設計缺失研判，並計算其混合氣流量、燃燒功率與空燃比三項性能參數。後續藉數值工具執行完整的幾何參數分析工作，考量參數包括空氣入口孔徑、主管與空氣入口孔徑之間隙、主管的長度及出口管徑，確認各項幾何參數對性能影響，提供混流器之設計參考與性能最佳化。數值計算與參數分析的結果顯示，各燃氣孔徑混流器之最佳化模型較原始模型於各轉速操作點，其空燃比皆接近理想值也符合本研究設計範圍內，這代表最佳化模型能趨近於完全燃燒，有效地減少污染的排放和提高燃氣爐具性能。
在混合氣流量與功率方面，3 mm燃氣孔徑混流器之流量與功率分別降低19%與5%，而較大的燃氣孔徑(4.2與5 mm)混流器之流量分別提高27%與36%，且功率也提高6%與8%；以3 mm燃氣孔徑混流器而言，為了使空燃比保持穩定必須犧牲火力的輸出，而4.2與5 mm燃氣孔徑之混流器能輸出更高火力，同時也大幅減少污染的排放和提高燃氣爐具性能。另外觀察流場及速度分佈可發現，最佳化之混流器皆穩定輸出均勻的混合燃氣供燃燒，且能有效地改善其內部的迴流缺失。至於有關噪音降低之成效，最佳化模型在入、出口處之噪音下降2 dBA以上，而頻譜圖顯示13葉產生之第一特徵頻(975 Hz)的聲壓值提高，但26葉造成之第一與二特徵頻(1,950及3,900 Hz)皆有明顯下降。綜合歸納上述成果，本研究設計之混流器應用於燃氣爐具上，成功地達到強化氣動性能與2 dBA降噪成果，且在特定的特徵頻有3 dB以上之降幅，能明顯看出最佳化後的性能改善成果，可供未來混流器之設計參考。

The goal of this research is to design a high-performance venturi gas mixer for meeting various heating needs of the gas-powered cooking burner, which is used to provide the extra heating output for commercial cooking utilization. Firstly, a venturi mixer prototype is proposed based on the application and geometric limitations. Then, flow fields and performance characteristics of this venturi gas mixer are visualized and assessed via CFD simulation under the high, medium, and low heating demands, which are supplied by fuel pipes with 3, 4.2, and 5mm diameters, respectively. Besides the fuel/mixing and velocity distributions, the performance of venturi gas mixer is analyzed and evaluated by the flowrate of air-gas mixture, the heating power generation, and the air-fuel ratio. Later, a comprehensive parametric analysis is executed on the venturi gas mixer to provide the corresponding influence on key variables, which include air inlet aperture, length and diameter of main tube, venturi exit diameter, and gap between air inlet and main tube.
Accordingly, three optimized gas mixers are constructed to generate different power outputs, and numerically evaluated for using LPG and NG gases as fuels. As expected, CFD calculations show that all proposed models can deliver a superior air-fuel ratio to ensure an efficient combustion for reducing the exhausted emission. Also, gas mixers with 4.2mm and 5mm diameter fuel pipes can deliver extra 28% and 36% flowrates of the air-fuel mixture, which result in 6% and 8% increases on the heating power, respectively. In addition, the flow circulation inside the venturi gas mixer is diminished significantly to prevent the unexpected burning accident. Moreover, the acoustic simulations are performed on these optimized gas burner sets including the venturi gas mixer and the gas blower. The calculated sound pressure levels (SPL) indicate that 2-dB noise reduction is recorded for all monitoring locations at the inlet and the outlet sides of gas-fired burner. In conclusion, this numerical investigation successfully establishes a systematic scheme to optimize the venturi gas mixer generating the extra air/gas mixture flowrate and the higher heating power at a low noise output under various operation points.

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