This paper investigated the microparticle deposition and distribution due to the presence of duct bends by employing the Eulerian approach with Reynolds stress turbulent model and a Lagrangian trajectory method. The air velocity, particle velocity and particle deposition velocity were validated with available experimental data. Several particle deposition ratios were proposed to describe the particle accumulation due to bends. Particle deposition velocities in and behind bends were analyzed numerically. It is found that bend walls with surfaces of higher capture velocity tend to accumulate more contaminant particles as seen with an increased factor of 1.2 times on particle deposition velocity. Particle deposition reaches a maximum value near bend outlet, e.g. 15.2 times deposition ratio for particles of d p=23μm, and decay exponentially to a status of fully developed deposition in approximately 10D length. Compared to traditional consideration of sole deposition in bends, a new general concept of total deposition including that in bends and behind bends is proposed to better describe the particle deposition induced by bends since the enhancement deposition ratios behind bends compose 42-99% in the total ratios for particles of d p=3-23μm. Furthermore, models of fast power and exponential decay trend are demonstrated to uncover the relationship among enhancement factor of deposition velocity behind bend, dimensionless distance behind bends and particle Stokes number. The present study can contribute to the understanding and controlling of contaminant aerosol flow behavior in ducts, e.g. particle sampling, removal and associated epidemiologic study between particle and human health.
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机译:本文采用雷诺应力湍流模型和拉格朗日轨迹法,采用欧拉方法研究了由于导管弯曲而导致的微粒沉积和分布。空气速度,粒子速度和粒子沉积速度已通过可用的实验数据进行了验证。提出了几种颗粒沉积率来描述由于弯曲引起的颗粒积累。数值分析了弯曲处和弯曲处的颗粒沉积速度。已发现,具有较高捕获速度的曲面的弯曲壁往往会积聚更多的污染物颗粒,这是颗粒沉积速度的1.2倍。颗粒沉积在弯曲出口附近达到最大值,例如d p =23μm颗粒的沉积比为15.2倍,并且在大约10D的长度内呈指数衰减至完全展开的沉积状态。与传统的折弯底面沉积的传统考虑相比,提出了一种新的总沉积的一般概念,包括折弯和折弯后方的沉积,以更好地描述折弯引起的颗粒沉积,因为折弯后的增强沉积比占总折弯比的42-99% dp =3-23μm的颗粒的比率。此外,建立了快速幂和指数衰减趋势模型,揭示了弯头后沉积速度的增强因子,弯头后无量纲距离与粒子斯托克斯数之间的关系。本研究可有助于理解和控制管道中污染物气溶胶的流动行为,例如:粒子采样,清除以及与人类健康相关的流行病学研究。
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