摘要

本研究主要探討液態金屬在縫隙型內混式霧化器中不同噴嘴出口長寬比(AR)下之霧化性能。霧化器出口面積為12mm2，噴嘴出口長寬比分別為2.1、3.0、6.9及12.0等。液態金屬噴霧先以液態氮冷卻成金屬粉末，再以INSITEC粒徑分析儀量測金屬粉末粒徑。本實驗所採用之液態金屬為鉛錫合金(錫63%，鉛37%)。實驗結果顯示，在相同操作壓力下液態金屬流量及金屬粉末粒徑隨霧化器噴嘴出口長寬比而有相當大之變化，例如在液態金屬操作壓力為4´105N/m2下，金屬粉末平均粒徑隨噴嘴出口長寬比由AR = 2.1增加到AR = 12.0，其粒徑SMD亦從SMD = 15.0mm增加到SMD = 22.0mm。在長寬比由AR = 2.1增加到AR = 6.9時，在45mm以下的顆粒體積百分比(V45-)由74.2%增加到82.5%，但當AR由6.9再增加到AR = 12.0時V45-則進一步減少到56.8%。實驗結果亦顯示，在長寬比AR = 12.0時，金屬粉末粒徑分布範圍較大，其粒度比為SR = 10.57，而長寬比AR = 6.9時，其粒度比則降至SR = 7.89，故知控制噴嘴長寬比可以有效降低金屬粉末粒徑分布的範圍。液態金屬流量亦隨噴嘴長寬比AR而有顯著之不同，在液態金屬壓力為4´105N/m2時，噴嘴長寬比由AR = 2.1增加到 AR = 6.9時，液態金屬流量由1.54kg/min降到0.7kg/min，但當AR由6.9增加至12.0時液態金屬流量又增加至1.19 kg/min。實驗結果亦顯示在噴嘴長寬比AR = 12下，當液態金屬操作壓力由2´105N/m2增加到3´105N/m2時，SMD由28.93mm降低到22.42mm，但是當液態金屬操作壓力繼續增加到5´105N/m2時，SMD均維持在22mm左右。另外，氣液壓力差亦為霧化之控制參數，實驗結果顯示當氣液壓力差由0.3´105N/m2增加到1.2´105N/m2時，SMD從30.24mm降低到20.94mm。由上述實驗結果顯示噴嘴長寬比為AR = 6.9時有最佳之霧化性能，而且在液態金屬操作壓力3´105N/m2及氣液操作壓力差1.2´105N/m2可以得到較佳之霧化品質。

Abstract
The dependence of performance on aspect ratios of a linear atomizer in the atomization of molten metal is characterized in this paper. The aspect ratio of the atomizer is 2.1, 3.0, 6.9 and 12.0 with the same cross sectional area of 12mm2. The metal powders are first collected in a liquid nitrogen bath. The metal powders are then measured by INSITEC Particle analyzer. The experiments on the atomization of eutectic metal (Sn63%, Pb37%) show that the metal flow rate and the particle size vary significantly under different aspect ratios even with the same operation pressure. For example, the Sauter mean diameter of the powder(SMD) increase from 15.0mm to 22.0mm as the aspect ratio (AR) increase from 2.1 to 12.0 in a test with metal pressure of 4.0´105N/m2. The volume of the powder with the size less than 45mm increases from 74.2% to 82.5% as the AR increases from 2.1 to 6.9, However, when the AR further increases to 12.0, the volume percentage of the powder with size less than 45mm decreases to 62.2%. The result also show that the particle size distribution of the metal powder is wider at AR = 12.0. Size distribution of the metal powder can be narrowed down by reducing the aspect ratio to AR = 6.9. The mass flow rate of molten metal also varies with AR. The molten metal flow rate decreases from 1.54kg/min to 0.7kg/min when AR increases from 2.1 to 6.9. However, The molten metal flow rate increases to 1.19 kg/min when AR further increases to 12.0. On a test with AR = 12.0, SMD decreases from 28.93mm to 22.42mm as metal pressure increases from 2.0´105N/m2 to 3.0´105N/m2. However, SMD remains at 22mm when the metal pressure further increases to 5.0´105N/m2. Results also show that SMD decreases from 30.24mm to 20.94mm as the pressure difference between gas and molten metal increases from 0.3´105N/m2 to 1.2´105N/m2. It can be concluded that the optimization performance of the atomizer can be optimized at AR = 6.9. Moreover, better atomization performance can be obtained at metal pressure of 3.0´105N/m2 and pressure difference between gas and molten metal of 1.2´105N/m2.

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