本研究探討水旋風分離器以串聯連接方式及操作條件對其分級效率之影響。採用直徑10 mm之水旋風分離器來分離玉米澱粉(Corn starch)及PMMA粒子，分別進行實驗量測與數值模擬分析。實驗結果顯示，無論增加第一個或第二個水旋風分離器之壓降、增加第一個或第二個水旋風分離器之分流比，皆可提高其分級效率與總效率，且可使最後溢流口之粒子濃度降低，達到固液分離的目的。以串聯方式連接水旋風分離器分離Corn Starch為例，在本研究之操作範圍內，最佳的操作條件為：第一個水旋風分離器之壓降為0.4 MPa、分流比為3.3，第二個水旋風分離器之分流比為1.57；在此條件下，溢流口之粒子濃度可以比使用單一水旋風分離器還要降低13%。 本研究並以FLUENT軟體模擬水旋風分離器內之流體速度與壓力分佈。由模擬之結果可以獲得平衡軌道理論的零速包絡面，可以證實在分離器中心空氣柱的存在，並可了解在vortex finder附近的粒子抄近路現象。兩相流的模擬結果亦顯示，增加水旋風分離器之分流比可以提高分級效率，而且有明顯的魚鉤現象出現，這和實驗結果有相同的趨勢；但是模擬的分級效率比實驗結果低了大約2倍，因此尚有進一步的改善空間。 Effects of operating conditions on the particle separation efficiency of multiple hydrocyclones are studied and discussed. Two 10 mm-diameter hydrocyclones installed in series are used in experiments and in computational fluid dynamics (CFD) analyses. Experimental results show that an increase in pressure drop or split ratio, whatever in the first or the second hydrocyclone, leads the partial separation efficiency to be increase and the concentration of the final overflow to be decrease. The optimum operating condition for the separation of corn starch suspension can be selected as: the split ratios are set as 3.3 and 1.57 in the first and the second hydrocyclone, respectively, and the pressure drop is set as 0.4 MPa in the first hydrocyclone. The particle concentration in the final overflow is 13% lower than that in the use of single hydrocyclone. The fluid velocity and pressure profiles in the hydrocyclone are simulated by computational fluid dynamics method. The locus of zero velocity in the equilibrium orbit theory, the air core in the center of hydrocyclone and the short-cut phenomenon near the vortex finder can also be simulated using FLUENT software. Although the tendency and the occurrence of fish-hook effect in partial separation efficiency curve agree with experimental data, simulation results are still two-fold lower than experimental data. It is necessary to improve the simulation method to obtain accurate data in the near future.