本研究以計算流體力學探討圓錐形擴流器對無閥式微泵性能之影響。研究的目的在於了解擴流器暫態流場與整流效率之關係，並找出最佳整流效率及其所對應的相關參數。文中針對擴流器長度1400～12000μ m，擴張角度5度～90度，致動頻率10Hz～1000Hz 等範圍作探討，並且選擇氨水、水、乙二醇三種黏滯度不同之工作流體。
研究結果發現，影響整流效率的原因與流道中渦流的形成及特性有
關。而影響渦流的主要因素為擴流器擴張角大小與致動頻率。擴張角越大，擴流器方向的流場越容易產生渦流，對整流效率是不好的影響。而增加致動頻率則會改變渦流生成的時機，低頻下整流效率並非最佳，隨著頻率之上升，整流效率亦隨之提升至最佳值，但超過最佳頻率後，增加頻率反而會降低整流效果。不同工作流體所對應的最佳致動頻率亦有所不同。從模擬結果可知，擴張角為10度，細長比範圍在7.5~10 的擴流器會有最佳的整流效率，若繼續增加擴流器長度，對整流效率並不會有任何幫助。以工作流體而言，黏滯度越低，整流效率越高。

A numerical investigation of conical diffusers for valve-less micropumps is presented.The primary goal is to understand the unsteady flow characteristics in the diffusers and to clarify the parameters which affect the rectification efficiency of the pump. The simulations are performed for diffusers with different lengths (1400-12000μm), diverging angles (5°-90°)and excitation frequencies (10-1000Hz). Three working fluids of different viscosities, namely ammonia, water, and ethylene glycol are considered.Numerical results show that the unsteady flows are always accompanied by theformation of vortices. The timing of the vortex formation and the variation of the vortices have a direct impact on the rectification efficiency. The diverging angle and the excitation
frequency are the major parameters which influence the behavior of the vortices. The larger the diverging angle, the easier the vortex formation in the diffuser flow direction; this has a drawback effect on the rectification efficiency. Increasing the excitation frequency will change the timing of the vortex formation and, therefore, the rectification efficiency. For a specific working fluid, an optimum value of the excitation frequency can
be found. The rectification efficiency is found to increase with the increasing excitation frequency, reaches an optimum, and then drops down fast thereafter. It is found that the conical diffuser with diverging angle of 10°and slenderness of 7.5-10 has the best flow rectification ability. Also, the rectification efficiency can be significantly increased by reducing the viscosity of the working fluid.

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