通风管道内棱纹沟槽壁面和静电场对细颗粒物沉积效应研究

Nowadays, large number of ultrafine particles (UFPs) and fine particles exist in outdoor of many metropolitan cities in China. When they readily transport to buildings through air-conditioning sytems, it will result in the adverse effect on public health. Understanding deposition in ventilation duct is important to evaluate human exposure indoors. If ventilated duct surface textures are properly modified by introducing finely V-shaped riblet-covered surfaces, the deposition of UFPs may be enhanced. Electrostatic field is also proven to be a very energy-conservative method to remove fine particles. Interestingly, these concepts can be integrated together to enhance deposition for UFPs inside ventilation systems. This idea motivates the proposed study. An in-house lattice Boltzmann (LB) based numerical framework will be employed in the proposed work to model the airflow and the results will be used for predicting fine particle deposition. The computational code will be verified by experiments conducted in proposed ventilation ductwork. Details turbulent properties over the V-shaped riblets as well as the pressure drop will be measured. The results will be compared with those predicted by the LB code. Monodisperse particles of sizes ranging from 20 nm to 300 nm will be generated. Particle deposition rate will be measured by sensitive fluorescent analysis. Various parameters will be calculated to evaluate the effectiveness of the enhanced deposition due to the V-shaped riblets and electret paper. This innovative approach has not been reported in literature. It will be helpful for gaining more fundamental understanding on particle deposition with the potential for improving indoor air quality.

目前，中国许多大城市经常出现细颗粒物和超细颗粒物浓度超标的情况，而这些颗粒物通过大型楼宇建筑的空调系统进入室内后，会对人体健康造成威胁。因此，关于增强通风管道内颗粒物沉积的研究对于降低室内污染有重要意义。借鉴以往的研究成果，V形棱纹沟槽壁面和静电场都有可能增加颗粒物在壁面的沉积。于是本申请项目将采用基于格子玻耳兹曼方法的数值模拟和实验相结合的方式，主要研究空调系统通风管道内V形棱纹沟槽对壁面附近紊流、流动压降以及粒径位于20-300nm之间的细颗粒物沉积的影响效应，还包括V形棱纹沟槽壁面与静电场联合作用对细颗粒物沉积的影响效应。本申请项目的研究将有利于开发改善室内空气质量的装置。

人大部分时间都在室内度过，室内环境空气的好坏直接关系到人的身体健康，而使环境中的空气过滤到可接受的水平需消耗大量的能源。因此，寻找到不仅能提供良好的室内空气，而且能使能源可持续发展的方法很重要。首次提出了使用 V 形棱纹沟槽壁面来增强细颗粒物沉积的方法。实验和数值模拟结合的方法研究 V 形棱纹沟槽壁面细颗粒物的沉积与其对流动的影响。为评价V 形棱纹沟槽壁面对颗粒沉积的效果，对比了相同条件下（湍流和层流时）的空风管中的颗粒沉积。研究了静电场的对细颗粒物沉积的影响，使用SMPS分别测量上下游的分级粒径下的颗粒浓度，计算颗粒沉降率与沉降速度以及棱纹沟槽壁面的性能比。开发了基于多松弛时间格子玻耳兹曼的模拟流动的方法，采用拉格朗日方法来模拟颗粒离散相的运动。模拟结果能很好的吻合模型实验值。主要结论如下：.1. V 形棱纹沟槽壁面能有效地增强颗粒的沉积。对于小于20 nm的颗粒，Re = 1240 时，在V 形棱纹沟槽壁面中的沉降速度是相同条件下在空风管中的7倍，而对于50 nm - 100 nm的颗粒，沉降速度是4.8倍。传统的过滤器，很难将小于20 nm的颗粒移除。只有很高效的过滤器才能过滤细小颗粒，而这也会带来较大的压力损失，压降可达300pa，而对于V 形棱纹沟槽壁面，压降与空风管相比，增加的不明显。这是本项目很重要的发现和应用。通过良好的设计棱纹沟槽壁面，可有效地避免较大的压降增加。此外，棱纹沟槽壁面结果显示颗粒物增强的沉降速度比和性能比都在层流时达到最高。.2.静电吸引力不是一种有效的增强超细颗粒物的方法。这可能是因为不带电的粒子和弱化的静电力。由于更小的颗粒比大颗粒有更强的布朗扩散能力，空风管中颗粒物的沉降速度随着颗粒粒径的减小而增加。空风管中不同粒径下的细颗粒物的沉降速度范围为 1.94×10-5 - 1.28×10-3 m/s。.3.除研究计划中最初的棱纹沟槽壁面外，也简要研究了另一种被动式增强颗粒沉积的方法——螺旋纽带。螺旋纽带的方法在强化换热领域被广泛地研究并应用。结果表明棱纹沟槽壁面比螺旋纽带能有更高的沉降速度比和更小的压力损失。