A Study of Inertial Effect on Particle Deposition in Wedge Flows

慣性效應在楔型板流中影響微粒附著率之研究

蔡瑞益(R. Tsai) ； 梁龍驥(L. J. Liang) ； 吳明誠(M. C. Wu)

《先進工程學刊》 9卷4期 (2014/10) Pp. 233-238

摘要

本文探討，慣性效應在氣流流經楔形板表面時，對微粒附著率的影響。其氣流流場考慮不可壓縮、穩態和層流流經一二維之Falkner-Skan楔形角。求解的方法是以相似分析法將質量、動量和微粒傳輸方程式，轉換成相似和非相似方程式，再輔以箱氏法及消去法，求得速度場和微粒濃度場，並計算微粒附著表面速率。一般慣性作用是影響大微粒（d_p≥0.1μm）之主要機制；反之，在小微粒（d_p≥0.1μm）則以布朗擴散為主。然而本文發現：在x值小，區域史托克數（方程式略，是微粒鬆弛時間和微粒之暫態時間的比值）較大時，慣性效應仍顯著的影響微粒附著率。故區域史托克數，仍可用以測量慣性效率之影響。結果發現：在楔形角度60和90度（m = 0.5和1.0）時，微粒之附著率會增加；然而，當楔形角度0和30度（m = 0和0.2）時，附著率則會稍微減少。

關鍵字

慣性效應 ； Falkner-Skan楔 ； 相似分析

並列摘要

A study of inertial effect on particle deposition onto wedge surfaces is reported. The aerosol flow is modeled as an incompressible, steady state and laminar flow over a two-dimensional Falkner-Skan wedge. Governing equations of the conservation of mass, momentum, and particle transport are transformed to be a system of similar and non-similar equations by similarity analysis and solved using box method associated with block-elimination. Usually particle deposition rates are controlled by inertia for particles larger than 1 μm and dominated by Brownian diffusion for small particles (d_p ≤ 0.1μm) having small relaxation time. However, the inertial effect may be still significance for small particles due to large Stk_x, which is the ratio between the particle relaxation time and the transient flow time along the x-coordinate, as x is small. The dimensionless parameter, Stk_x, is called the local Stokes number and can measured the inertial effects. Results show that the inertial effect may increase the particle deposition for wedge angles 60 and 90 degrees (m = 0.5 and 1.0) but somewhat decrease for the angles 0 and 30 degrees (m = 0 and 0.2).

並列關鍵字

inertial effect ； Falkner-Skan wedge ； similarity analysis