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Visualization of Mixing in Microchannel Flow with Pressure Perturbation
本研究的混合實驗參數，流量設定為5~15 mL/hr、頻率設定為1~60 Hz並且固定三種壓力振幅分別是1.44 kPa、1.84 kPa、2.53 kPa，以探討不同流量下，壓力干擾的混合效益。由實驗結果發現，對稱型和非對稱型結構在頻率介於15 ~ 20 Hz時，混合效益會隨著頻率增加而增加。當壓力振幅分別設定1.44 kPa、1.84 kPa時，在非對稱型結構中頻率介於20 Hz~35 Hz會出現較好的混合效益(不同流量分別對應不同的頻率)，然而超過此範圍的頻率混合效率就會有下降的趨勢。在對稱型結構的實驗則發現頻率在20Hz以上，混合效益會有一段下降然後再上升的結果。當壓力振幅在2.53 kPa、頻率在20 Hz以上，兩種結構的混合效益會達到90%。混合效益與頻率的關係可以藉由可視化方法觀察不同流量或流道幾何(對稱型和非對稱型)的結果得知。
Enhancement of mixing of two fluid streams in a T-type microchannel perturbed by oscillating pressure has been studied experimentally. The pressure perturbation was introduced from the secondary channels in a symmetric or asymmetric arrangement located downstream of the junction where the two streams started to meet. The working fluids are the ferric chloride and ammonium thiocyanate solutions. When the two fluids mix they react to change from light yellow to dark red. The mixing process was monitored using the flow visualization technique and the quantification of mixing efficiency of the fluids was obtained based on the color level of the flow-field images. Measurements of the mixing efficiency have been made for perturbation pressure amplitudes ranging from 1.44 to 2.53 kPa and frequencies up to 60 Hz, for flow rates of 5-15 mL/hr. It is found that the mixing efficiency can be largely enhanced by introduction of pressure perturbations and the enhancement becomes more significant at larger oscillation amplitude. The efficiency increases rapidly with an increase of the frequency in the low range (below 15-20 Hz) then a maximum may be reached at a frequency between 20 to 35 Hz for smaller oscillation amplitudes. The dependence of mixing efficiency on the oscillation frequency is presented and discussed associated with the flow visualization results for the flow rates as well as the symmetric and asymmetric arrangements of the perturbations.
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