本研究探討各種不同噴嘴結構之二氧化碳雪花產生裝置之設計及特性，包括一段式噴嘴，漸縮型、直管型、直管過濾型與漸縮直管型之二段噴嘴等不同設計，以及三種不同內徑之二氧化碳形成腔體設計，分別進行流量測量、粒子影像測速儀(PIV)、流場觀察與噴霧品質診斷。實驗結果顯示液態二氧化碳流量在相同的噴嘴本體孔口與不同形成腔體條件下，其通過之二氧化碳流量值皆約介於0.9~1.1g/s，顯示二氧化碳噴流之流量取決於噴嘴本體之孔口直徑大小，雪花形成腔體之設計對二氧化碳之流量影響較小，其原因在於雪花形成腔體中之液態二氧化碳汽化未足以造成過大之升壓現象並影響液態二氧化碳流量及二氧化碳雪花噴流速度。實驗結果亦顯示，使用一段噴嘴其速度較慢粒徑較小且濃度較高，當增大雪花形成腔體管徑可有助於降低雪花飛行速度與減小雪花粒子並增高其雪花濃度，此二氧化碳雪花噴流為連續式之中空結構噴流，並於雪花形成腔體管內有良好預混效果，於腔體管徑10mm下其噴霧錐角為39度，遮蔽面積較大，故適合於冷卻方面之運用。於使用二段噴嘴之雪花形成腔體雪花噴流皆屬於間歇式之兩相紊流實心結構噴流，其流場速度分佈與擾動強度較為均勻具整合流場之作用並可減少能量損耗有效提升二氧化碳雪花流場之粒徑及雪花飛行速度，當二段噴嘴孔口越小其雪花飛行速度越快，於本研究以形成腔體直徑14mm使用漸縮型二段噴嘴出口從5mm減小至3mm時，噴霧粒子平均速度可由10.31m/s提升至22.3m/s；此外，於本實驗亦可證明直管過濾型二段噴嘴之設計可達預期過濾大顆粒雪花之效果，本設計可有效過濾5%之大於300μm的二氧化碳雪花顆粒，此型之噴霧錐角約為25度；於漸縮型二段噴嘴之噴流流場，由於漸縮管之噴流集中效應，使得噴口出口處明顯有高濃度二氧化碳雪花分布，故噴流噴霧錐角小於過濾直管型二段噴嘴，由25度降為20度，由於二段噴嘴之加速效應，其二氧化碳雪花動量大幅增加，故可應於光電半導體之清洗製程中。

This paper investigates the characteristics of CO2 snow formation chamber with secondary nozzle. The design of CO2 snow formation chamber including primary nozzle, secondary nozzle of convergent type, straight type, straight with filter type, convergent-straight type and the three kind of different diameters has been discussed. Flow field visualization and spray quality are observed by particle image velocimetry(PIV). Results show that the mass flow rate is around 0.9~1.1 g/s when formation chamber installed. The design of formation chamber effects CO2 snow jet slightly. The mass flow rate is controlled by orifice diameter. It results from the liquid CO2 in the formation chamber didn’t vaporized enough to rise the chamber pressure and effects the velocity as well as mass flow rate of CO2. Result also shows that the particles with smaller size, lower velocity and higher concentration appear in the case of primary nozzle. Enhancing the diameter of formation chamber could reduce the snow size and increase the concentration of CO2-snow.The CO2 snow with primary nozzle is continuity jet. It is applicable in cooling. Impulse jet takes place in the case of secondary nozzle applied. The snow size is larger than the case of CO2 snow jet with primary nozzle. Moreover, straight with filter nozzle had filter large CO2 snow particle. The design of this paper can partially filter the particle size larger than 300μm. For the flow field of convergent secondary nozzle, high concentration CO2-snow distribute near the orifice of formation chamber due to the jet is centralized by convergent channel. The CO2 snow momentum is enhanced obviously due to the acceleration of secondary nozzle. The mechanism could be used in cleaning process.

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