氣體霧化法為工業製造金屬粉末之核心技術，傳統氣霧法製程需要較高之氣體操作壓力(>1MPa)，導致設備和氣體消耗量方面花費成本甚多。本研究主要分為三部分來探討氣體輔助霧化器之霧化特性。第一部分先以數值方法模擬噴嘴之二維流場，以建立噴嘴在不同壓力下之流場特性。第二部分進行冷模實驗，以水作為霧化介質，探討不同之霧化氣體壓力、氣液質量比以及輸送管孔徑對其霧化特性之影響，並驗證數值模擬之結果。第三部分進行金屬霧化實驗，以鉛錫合金Sn63Pb37為霧化材料，研究霧化氣體壓力及金屬熔湯溫度，對金屬粉末粒徑之影響，並從金屬粉末SEM照像圖印證粉末粒徑及觀察粉末之表面特性。
噴嘴流場數值模擬結果顯示，於較低霧化氣體壓力操作條件下，透過噴嘴漸縮漸擴之結構設計可令氣流速度達到超音速。當氣體壓力從1.0kg⁄cm^2 增加至3.5kg⁄cm^2 時，產生之最大氣流速度由235.9 m⁄s增加至415.6( m)⁄s。結果亦顯示此噴嘴結構可產生負壓狀態，其負壓值由-0.34kg⁄cm^2 變化至-0.28kg⁄cm^2 ，此乃本研究噴嘴操作之重要條件。冷模實驗結果顯示，隨霧化氣體操作壓力遞增，噴霧之平均粒徑有降低之趨勢。當霧化氣體壓力為3.5kg⁄cm^2 及輸送管之孔徑為2.0mm時，其Dv50可降低至6.88μm。金屬粉末實驗結果顯示，當金屬熔湯溫度為450℃時，氣體壓力從1.0kg⁄cm^2 增加至3.5kg⁄cm^2 ，則金屬粉末之Dv50從65.68μm降低到14.30μm。因此，利用氣體輔助霧化法製程，可以在低壓條件下製造微細之金屬粉末，是具有最佳效益之製造方法。

Gas atomization is capable for metal powder production for industrial application. However, the conventional gas atomizers require higher gas operating pressure (> 1 MPa), which results in more cost in facilities and gas consumption. In the present study, an air-assist atomizer with low gas pressure was investigated for metal powder production. The gas was accelerated to supersonic speed through the convergent–divergent geometry inside the nozzle and impinged on the liquid. In order to investigate the performance this air-assist nozzle, three steps for analyzing the nozzle behavior were performed. First, the gas flow behavior was analyzed by simulation, and it was discussed that the field characteristics were produced by nozzle under various pressure. Second, it was conducted by cold-model experiments, and we investigated the influence of atomization characteristics under various condition, i.e., gas pressure, gas-to-liquid mass ratio and the inner diameter of the delivery tube. Besides, it was showed the comparison of the delivery tube tip pressure for experimental and simulate result. Finally, it was conducted by atomization on the experiment of metal powders. The experimental parameters with Sn63Pb37 metal powders included gas pressure and molten metal temperature. For characterization the metal powders was analyzed by scanning electron microscopy.
From the results of the simulation, it can be seen that air is accelerated to supersonic speed through the convergent –divergent geometry of the nozzle even at low gas pressure. The maximum speed was increased from 235.9 m/s to 415.6 m/s with the gas pressure increasing from 1.0 kg/cm2 to 3.5 kg/cm2. In cold-model experiments, the results showed that the particle diameter of the water decreased by further increasing atomising pressure. The minimum volume mean diameter (Dv50, μm) can be achieved at 6.88μm when gas pressure was 3.5 kg/cm2 and inner diameter of the delivery tube was 2.0 mm. In metal powder experiments, the powder size was decreased from 65.68μm to 14.3μm when the gas pressure increasing from 1.0 to 3.5 kg/cm2 at higher melt temperature 450 ℃. As a result, the optimum efficiency for the production of fine metal powders can be produced by the air-assist atomizer.

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