本研究以實驗方法探討單粒徑液滴產生之現象，主要設備為單粒徑液滴產生器，其操作原理係以一訊號產生器產生一正弦波電壓，經變壓器放大後通入壓電片使壓電片產生振動，產生之振動經黏附於壓電片之振動棒，傳入噴嘴上游液體儲存槽內之液體，振動由孔口噴出之液體以產生單粒徑液滴，工作流體包括水溶液、甘油溶液及熔融金屬液(Sn63 Pb37)。結果顯示，欲解釋黏度及表面張力對單粒徑液滴產生之工作頻寬的影響，可將流體分為低黏性及黏性流體兩大類，分割界限約在25 cp至 60 cp左右。低黏性流體其黏度改變對工作頻寬影響不大，因為黏度不同之液體，其各頻率之擾動成長率(disturbance growth rate)相近；表面張力改變對工作頻寬影響亦不大，因為表面張力不同之液體，各頻率的擾動成長率成等比例變化。黏性流體黏度增加或表面張力降低時，工作頻寬中心點的波數(wave number)值會變小，因為最佳波長(optimum wave length)增加；此外，最大及最小工作頻率會降低，因為黏度增加或表面張力降低時，流體的擾動成長率會變小，較高黏度或較低表面張力之流體，在較低黏度或較高表面張力之流體的最大工作頻率附近，外加人工激擾波之擾動成長率變小的程度比天然擾動波之擾動成長率(最大擾動成長率(maximum disturbance growth rate))變小之程度大，因此外加人工激擾波會被天然擾動波超越，使單粒徑液滴無法產生，造成最大工作頻率降低；相反地，在較低黏度或較高表面張力之流體的最小工作頻率附近，外加人工激擾波之擾動成長率變小的程度比天然擾動波之擾動成長率變小的程度小，因此天然擾動波會被外加人工激擾波超越，使單粒徑液滴可在更低之頻率產生，造成最小工作頻率降低。另外，Ohnesorge number相近之流體工作頻寬相近，因為最佳波長(optimum wave length)及擾動成長率(disturbance growth rate)係Ohnesorge number之函數。

在單粒徑熔融金屬液滴研究方面，結果顯示高氧氣濃度之環境會阻礙單粒徑熔融金屬液滴之形成，甚或熔融金屬液柱之斷裂，它們可進一步說明如下：受不同氧氣濃度影響之熔融金屬液柱的斷裂情況，大致可以第1 臨界氧氣濃度(1st critical oxygen concentration, [O2]*1st)及第2 臨界氧氣濃度(2nd critical oxygen concentration, [O2]*2nd)分為三個區域，它們分別為“斷裂區”(breakup regime)、“不完全斷裂區”(incomplete breakup regime)及“不斷裂區”(breakup failure regime)。液柱之直徑為152 m時，[O2]*1st約為500 ppm，氧氣濃度在[O2]*1st以下，熔融金屬液柱可順利斷裂成液滴，並在某些頻率下產生單粒徑液滴，如低黏性流體，[O2]*1st亦是熔融金屬液柱自然破裂區域的限制，氧氣濃度在此值以上，熔融金屬液柱無法順利斷裂成液滴而是呈條狀斷裂，不過只要加入激擾，在某些頻率下液柱仍可順利斷裂產生單粒徑液滴，熔融金屬液柱之行為在表面張力高達48010-3 N/m之情況下，即在斷裂區之情況，及液柱表面有大形氧化島嶼之情況下，即在不完全斷裂區之情況下，仍可滿足Rayleigh理論，在電壓500 volt之情況下，工作頻寬於波長D < <3R,opt之範圍內；然而，如果氧氣濃度到達[O2]*2nd以上，即使加入激擾，熔融金屬液柱亦不斷裂，液柱之直徑為152 m時，[O2]*2nd約為900 ppm，此現象不符合Rayleigh的理論，Rayleigh並未預測斷裂會因表面張力變化而終止，表面張力因氧化而降低之敘述並不能解釋液柱不斷裂之現象，此現象必須整合Haj-Hariri等人(2000) 及 Artem’ev等人(1991)之研究解釋---即隨著氧氣濃度之增加時，島狀氧化物會成長並連結，直到在臨界濃度時，到達高表面撓剛度(surface flexural rigidity)，導致斷裂過程突然終止。在不同直徑下[O2]*1st及[O2]*2nd隨熔融金屬液柱直徑的減少而升高，此現象係因液柱直徑變小時，斷裂長度變短及毛細力(capillary force)增強之原故。

More than seventy years has passed since Weber’s theory was proposed to modify Rayleigh’s instability theory in 1878. However, the influences of viscosity and surface tension on the frequency band of mono-sized droplet generation have not been clearly explained. Also, it is not assured whether the frequency band of mono-sized droplet generation of “molten metal (Sn63 Pb37)” can be described by both theories. Thus, this dissertation tries to clarify above questions through the experiments. The working fluids include the water solutions, glycerine solutions and the molten metal (Sn63 Pb37). The major apparatus is a mono-sized droplet generator, which breaks a laminar stream of fluid to produce mono-sized droplets through the forced excitation by a piezoelectric disk. The mono-sized droplets are formed if the excitation is applied in the proper frequency range. The results show the fluids can be divided into the low viscosity and viscous fluids to describe the effect of viscosity and surface tension on the working frequency band. The separation margin is around 25 cp to 60 cp. For low viscosity fluids, the influence of viscosity variation on the working frequency band is not significant because the fluids with different viscosities have the same disturbance growth rate for each disturbance wavelength. The influence of surface tension variation on the working frequency band is not obvious because the disturbance growth rates for two different fluids have the same ratio for each disturbance wavelength. For viscous fluids, as the viscosity increases or the surface tension decreases, the wave number at the center of the working frequency band decreases because optimum wave length increases. The maximum working frequency decreases because Relative growth rate ratio is smaller than 1. The minimum working frequency decreases because Relative growth rate ratio is bigger than 1. Additionally, the fluids with the same Ohnesorge number have the same working frequency band because both optimum wavelength and growth rate are the function of Ohnesorge number.

In the investigation of mono-sized molten metal droplet generation, the results show that the conditions under which molten metal jet is affected by the increase of oxygen concentration can be approximately divided into three regimes by two “critical oxygen concentrations, [O2]*.” They are the “breakup regime,” the “incomplete breakup regime,” and the “breakup failure regime,” respectively. [O2]*1st is equal to around 500 ppm with a diameter of 152 m and is also the limit of the breakup regime at the natural breakup of a molten jet in this research. As long as the excitation is applied to the jet, the molten metal jet can completely break up again in a certain frequency band. However, if [O2]*2nd is reached, the molten metal will never be broken up, even when the excitation is applied. [O2]*2nd is around 900 ppm with a diameter of 152 m. The behaviors of molten metal jets conform to the Rayleigh’s theory in “breakup regime” and “incomplete breakup regime” under excitation. Rayleigh’s theory is not applicable in breakup failure regime because it does not predict any breakup failure due to the change of surface tension. It can be explained by integrating the research of Haj-Hariri and Poulikakos (2000), and Artem’ev and Kochetov (1991)--- i.e., the oxide film islands grow and join until reaching high surface flexural rigidity at the critical oxygen concentration, and resulting in a sudden failure of the breakup process

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