本研究討論水旋風分離器的幾何結構以及操作條件對其分級效率之影響。以直徑10 mm之水旋風分離器為例，使用不同種類的粉粒體，分別進行實驗與數值模擬分析。實驗結果顯示，增加操作壓降、底流與溢流流量之分流比、溫度或降低進料濃度之條件下，皆可提高其分級效率與總效率，但溫度之影響並不顯著。在所有實驗之分級效率圖中，均出現魚勾現象，有一最低分離效率出現。比較模擬與實驗之分級效率曲線，顯示二者之最大誤差值約為25%。 採用數值模擬方法，可求出水旋風分離器之速度、壓力分佈及粒子運動軌跡模擬，並了解各操作條件下之差異。模擬之結果顯示，粒徑大小及進料位置對於粒子之運動軌跡均有明顯的影響。不同的幾何結構之水旋風分離器會有不同的分離效率及分流比；增加溢流口直徑，分級效率會下降，而增加底流口直徑，則可提高分級效率。進口截面為矮胖形(寬高比為25:16)比瘦高形(寬高比為16:25)有更好的分級效率。 Effects of geometric structure of hydrocyclone and operating conditions on the classification efficiency of particles are studied and discussed. A 10 mm-diameter hydrocyclone is installed for particle classification. Four kinds of particles with different size distributions and physical properties are used in experiments and in computational fluid dynamics (CFD) analyses. Experimental results show that an increase in pressure drops, split ratio, or suspension temperature or a decrease in feed concentration leads both the partial separation efficiency and overall separation efficiency to be increase. However, the effect of suspension temperature is trivial. The Fish-hook effect in partial separation efficiency occurs in all experimental results. The maximum deviation of the partial efficiency curve between the simulation results and experimental data is about 25%. The velocity and pressure profiles and the trajectories of particles in the hydrocyclone are simulated by computational fluid dynamics method and discussed. The simulation results show that the diameter and the feed position of particles play important roles on the particle trajectories in hydrocyclone. The flow pattern, the partial separation efficiency and the split ratio are strongly dependent on the geometric structure of hydrocyclone. Increasing the diameter of overflow pipe or decreasing the diameter of underflow pipe leads to a lower partial separation efficiency. A rectangular inlet which width exceeds height results in higher partial separation efficiency than one which height is longer.