本研究擬探討二氧化碳雪花產生裝置在同軸型氮氣輔助噴嘴與氮氣輔助氣流作用下之效應。所採用之輔助氣流為對衝式噴流之設計，探討輔助氣流之壓力與輔助噴嘴口徑對雪花粒徑及流場之影響。雪花粒徑由Malvern粒子分析儀量測，流場以粒子影像測速儀(PIV)量測，進行流場觀察與噴霧品質診斷。實驗結果顯示當氮氣輔助噴嘴未加入氮氣，且氮氣輔助噴嘴直徑等於或小於二氧化碳雪花噴嘴出口直徑時，因噴嘴整體出口減小，使得噴流較為均勻集中，噴霧錐角減小且二氧化碳雪花之流場速度與擾動強度提高，且增大雪花粒徑並減小其雪花濃度。當氮氣輔助噴嘴加入氮氣輔助氣流，無論氮氣輔助噴嘴出口尺寸大於或小於二氧化碳雪花噴嘴直徑，皆會對其二氧化碳噴流產生影響，二氧化碳雪花流場外部因二氧化碳低溫而凝結之水氣層明顯減少，代表氮氣輔助氣流對二氧化碳雪花流場有包覆性的作用；在同尺寸之氮氣輔助噴嘴下，使用越高壓力之輔助噴流，其二氧化碳粒徑與雪花飛行速度皆上升，但其雪花濃度與噴霧錐角皆減小。在一定氮氣輔助氣流壓力下，使用越小直徑之氮氣輔助噴嘴，其變化與上述相似，二氧化碳雪花粒徑增大，二氧化碳雪花流場速度分布與擾動強度提高，但其雪花濃度及噴霧錐角皆減小。實驗結果亦顯示，使用較小直徑之氮氣輔助噴嘴及較高之氮氣輔助氣流壓力，可有效提高二氧化
碳雪花動能與粒徑大小，並使噴霧流場更為集中，故能夠對二氧化碳雪花之粒徑及流場產生控制之效果。

This paper investigates the characteristics of CO2 snow formation chamber with Co-axial Type Injector. The design of Co-axial Type Injector including nitrogen auxiliary nozzle in five kinds of different diameters and auxiliary opposed type nitrogen induction system with four different gas pressures has been discussed. Flow field visualization and spray quality are observed by particle image velocimetry(PIV). Result shows that when Co-axial Type Injector uses nitrogen auxiliary nozzle only without auxiliary opposed type nitrogen induction system, and the diameter of the nitrogen auxiliary nozzle is less than or equal to CO2 snow formation chamber, CO2 snow has particles with larger size, higher velocity and lower concentration, and the CO2 snow jet would be centralized by smaller channel. Result also shows that when Co-axial Type injector uses both nitrogen auxiliary nozzle and auxiliary opposed type nitrogen induction system, no matter the diameter of the auxiliary nozzle is less than or more than CO2 snow formation chamber, the injector affects CO2 snow, it could reduce water layer caused by low temperature of CO2 snow jet. At the same diameter of nitrogen auxiliary nozzle, higher pressure of nitrogen could increase CO2 snow particles and velocity; this phenomenon takes place in the same pressure of gas nitrogen with smaller nitrogen auxiliary nozzle diameter. Decreasing the diameter of nitrogen auxiliary nozzle and increasing auxiliary nitrogen pressure could enhance the snow size and velocity, reduce the concentration of CO2-snow, The CO2 snow momentum is enhanced obviously due to the acceleration of Co-axial Type Injector. The particle size and jet velocity of CO2-snow can be controlled.

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