低速液滴撞擊浴池的運動行為

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题名:	低速液滴撞擊浴池的運動行為
作者:	林鶴育;Lin, He-Yu
贡献者:	機械工程學系
关键词:	聚結;彈跳;馬蘭戈尼效應;表面張力波;Coalescence;Bouncing;Marangoni effect;Surface tension waves
日期:	2023-11-09
上传时间:	2024-09-19 17:44:04 (UTC+8)
出版者:	國立中央大學
摘要:	液滴撞擊浴池時會發生聚結、飄浮、飛濺和彈跳，其中彈跳現象會顯著影響技術應用，如：引擎燃料噴射、噴墨列印和噴墨塗裝等。因此，本論文著重觀察液滴在不同撞擊速度與不同浴池溫度下的彈跳現象行為。液滴和浴池均使用相同的矽油。本文研究針對液滴最大穿刺時間、彈跳時間、彈跳週期、穩定時間、表面波分析、停留時間隨實驗條件的變化情形進行觀察。最大穿刺時間、彈跳時間、週期和穩定時間與韋伯數及溫差無關。最大穿刺時間和彈跳時間隨著液滴直徑的增加而增加，而週期和穩定時間則隨液滴直徑增加略微增長。波速則與韋伯數、直徑和溫差無關。另一方面，液滴停留時間會隨著溫差的增加而增加，並且隨著撞擊速度的增加而有增長的趨勢，僅少部分結果例外。而針對實驗數據進行無因次分析進一步發現，將最大穿刺時間對毛細時間尺度(  s ) 無因次化後會變成一個常數。無因次彈跳時間、無因次彈跳週期和無因次穩定時間會隨著液滴直徑的增加而稍微減小。無因次波速則介於表面張力波相速度與群速度之間。為了分析熱毛細流的影響，我們引入了延遲時間 d  ，來描述相對於均溫情況下停留時間的增加，並以溫度差來定義馬蘭戈尼數 Ma。結果顯示 / d th   會隨 Ma 的增加而增加。而無因次延遲時間則與液滴直徑和速度無關。實驗結果顯示，浴池溫度的升高對於液滴彈跳這樣的短期行為並沒有影響，但會延長液滴在浴池上飄浮的時間。;When droplets impact a liquid pool, they may undergo some processes such as coalescence, floating, splashing, and bouncing. The bouncing phenomenon significantly affects various technological applications such as engine fuel injection, inkjet printing, and inkjet coating. This study focuses on the bouncing behavior of droplets upon liquid pools at different impact velocities and increasing pool temperatures. The droplets and liquid pools were of the same silicon oil. We conducted the experiments on various aspects, including the penetration time, bouncing time, bouncing period, settling time, surface wave, and residence time, in response to changes in experimental conditions. The penetration time, bouncing time, bouncing period, and settling time were unrelated to the Weber number and temperature difference between the droplet and liquid bath. The penetration and bouncing times increased with an increase in droplet diameter, and the bouncing period and settling time exhibited a slight increase with increasing droplet diameter. The wave speed was unrelated to the Weber number, diameter, and temperature difference. On the other hand, the residence time increased with an increase in temperature difference and showed an increasing trend with increasing impact velocity, with only a few exceptions in the results. Further analysis of the experimental data through dimensionless analysis revealed that the dimensionless penetration time scaled by capillary time  th reduced to a constant. The dimensionless bouncing time, bouncing period, and settling time slightly decrease with an increase in droplet diameter. The dimensionless wave speed fell between the surface tension wave phase and group velocities. To analyze the influence of thermocapillary flow on droplet floatation, we introduced a delay time d  indicating the increase in residence than the uniform temperature case and defined the Marangoni number based on the temperature difference. The results showed that / d th   increases with the increase in Ma . The dimensionless delay time, iii however, is unrelated to droplet diameter and velocity. Experimental results revealed that increased bath temperature had no impact on the short-term behaviors of droplet bounce but prolonged the droplet floatation above the bath.
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