摘要
本研究主要目的為探討雷諾數在100~1500 的範圍內，平板形微擴流
器/噴嘴之壓力損失係數與流場變化。利用計算流體力學軟體FLUENT 針對細長比為2.5~15，擴張角為5°~100°之平板形擴流器/噴嘴進行穩態流場模擬，瞭解擴流器/噴嘴損失係數與流場變化之間的關係，並計算擴流器效率。同時進一步探討擴流器/噴嘴元件兩側銜接直管或儲液槽對損失係數及流場的影響。結果發現，就擴流器方向的流動而言，流場的分離導致回流的產生，不僅改變了分離點之後的速度分布，也一定程度降低了壁面剪應力的大小，造成擴流器損失係數在小擴張角及大擴張角範圍內呈現相反的變化趨勢。而噴嘴損失係數隨擴張角的變化則較單純，損失係數隨擴張角的增加而下降。擴張角在30° 以下，細長比為7.5 之擴流器/噴嘴元件，其擴流器效率均大於一，其中當擴張角為10° 時，擴流器效率為最佳。若增加其細長比，則可明顯改善擴流器效率。反之，若擴張角在50° 以上，則擴流器效率小於一，且其整流效率相當不理想。

Abstract
The primary purpose of this study is to investigate the pressure loss coefficient and the flow behavior of planar micro-diffusers/nozzles at low Reynolds numbers between 100 and 1500. Steady flow simulations of the diffusers/nozzles with diverging angles ranging from 5° to 100° and with slenderness ranging from 2.5 to 15 are done by using the computational fluid dynamics package FLUENT. Computational results help to identify the relationship between the pressure loss coefficient and the flow behavior and are used to calculate the diffuser efficiency. We also compare the difference between the diffusers/nozzles connected between two reservoirs and two
parallel ducts. Results show that, in the diffuser direction, flow separation induces a back flow and changes the velocity distribution and, therefore, the magnitude of wall shear stress after the separation point. These effects lead to opposite trends of the variation of pressure loss coefficient for small and large diffuser angles. On the other hand, the pressure loss coefficient of the nozzle flow simply decreases with increasing diverging angle for all Reynolds numbers. For diffusers/nozzles with a fixed slenderness of 7.5 and diverging angles less than 30° , the diffuser efficiencies are found all greater than one. The optimal efficiency of the diffuser is found at the diverging angle of 10°
and can be further improved by increasing the slenderness. For diverging angles greater than 50° , the diffuser efficiency is less than one and results in a poor rectification efficiency.

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