新型入口和出口設計對旋風分離器性能的影響

Abstract

旋風分離器利用慣性原理分離氣流中固體顆粒，其分離機制主要依賴雙渦流結構流場所驅動的顆粒分離行為，然而傳統使用的Stairmand旋風分離器設計，使用簡化的進出口幾何結構，導致雙渦流結構不盡完美。本研究採用計算流體力學(CFD)模擬方法，分析添增不同進出口設計改善後的旋風分離器之性能和流體動力學。進一步透過流固雙向耦合的 CFD-DPM 數值模擬方法，分析顆粒運動。針對彎管出口、彎曲入口、分隔式入口及分流器設計等四種類型之進出口幾何結構，分析旋風分離器分離效率與壓力損耗，並討論壁面剪切力、壁面侵蝕率、流場速度分布與漩渦偏心率、進口速度與顆粒分布等潛在因素。 模擬結果顯示，彎管出口方向與入口正交(90°)時，其截切粒徑(Cut size)與分離尖銳度(Sharpness)表現最佳；分隔式入口能改善局部非理想渦流現象，分離效率優於Stairmand旋風分離器及彎曲入口設計。分流器(Flow divider)利用分隔板與外壁內縮的幾何設計，能提升入口外側的氣體速度及顆粒質量流率，能有效消弭局部二次迴流現象，促使外側的近自由渦流(Quasi-free vortex)於趨近完全發展狀態，可使旋渦偏心率降低約 50%，改善其流場結構與分離性能。此外，本研究亦發現入口壁面之平均剪切力與截切粒徑具高度相關，過高壁面剪切力反而不利於分離效率；顆粒濃度分布方面，2毫米的分流器外壁內縮厚度可改善圓錐底部偏心迴流，並降低中心濃度；顆粒壁面侵蝕方面，適當增加分流器外壁內縮厚度可降低總侵蝕率，惟過厚則會增加圓錐處的侵蝕。 綜合各項分析，本研究提出於入口加裝2毫米外壁內縮厚度之分流器為最佳設計，對2 μm粒子的分離效率由56.74%提升至77.4%，且截切粒徑由1.87 μm下降至 1.23 μm。

Stairmand cyclones are commonly utilized in industrial applications to separate particulate matter from gas streams based on the inertia force. Its separation mechanism mainly relies on the flow behavior driven by a double-vortex structure. However, the conventional Stairmand design simplifies the inlet and outlet geometry. In this study, Computational Fluid Dynamics (CFD) is employed to analyze the performance and flow dynamics of Stairmand cyclones using various inlet and outlet designs. A two-way coupled CFD-Discrete Phase Model (CFD-DPM) simulation approach is used to evaluate the effects of different configurations — namely, elbow outlets, curved inlets, segmented inlets, and flow-divider inlets — on the cyclone’s separation efficiency, pressure drop, wall shear stress, erosion rate, and double-vortex eccentricity. Simulation results show that the cyclone with the elbow exit oriented orthogonal to the entrance direction demonstrates better performance in terms of the cut size and separation sharpness. The segmented inlet design can effectively mitigate local non-ideal vortex structures, with higher separation efficiency than both the conventional Stairmand cyclone and the curved inlet design. By adjusting the geometry of the flow divider and its outer wall thickness, the gas velocity and particle mass flow rate near the outer inlet region are increased, thereby suppressing local secondary recirculation flows. This promotes the development of a near-free vortex structure in the outer region right from the inlet section and reduces vortex eccentricity by approximately 50%, significantly improving separation performance. This study reveals a strong correlation between the average wall shear stress near the inlet and the cut size, where excessive shear stress negatively impacts separation efficiency. Regarding particle concentration distribution, a 2 mm outer wall thickness is found to diminish eccentric recirculation at the bottom of the conical section and reduce central particle concentration. In terms of wall erosion, an appropriately increased outer wall thickness helps lower overall erosion rates; however, overly thick walls may increase erosion in the rotational zone. To conclude, this study proposes an effective 2 mm-thick outer-wall flow divider design, which enhances the separation efficiency for 2 μm particles from 56.74% to 77.4%, and reduces the cut size from 1.87 μm to 1.23 μm.