室内沉积颗粒再悬浮的几种力学激扰机制

Suspended particles in air are of great impacts to human health. Jet flow from air terminal devices or intensive human respiratory activities such as cough and sneezing, can result in flow disturbance as well as resuspension of indoor deposited particles. The cleaning activities like sweeping floor and flapping clothes can also induce particle resuspension, which leads to content increase of suspended particles within air. The resuspension of deposited particles occurs when the particles detach from the adhering surfaces, subject to the interaction of the gravity, adhering and hydraulic forces, etc. This project attempts to disclose the mechanism of flow disturbance and its inducement to particle resuspension by various mechanical perturbation including jet flow, cleaning and flapping activities. Both computational fluid dynamics (CFD) and particle dynamics models will be developed to predict the particle detachment from the adhering surface, as well as the rolling, sliding and subsequent lifting of particles stage by stage. To verify accuracy of the numerical models, the corresponding experimental tests are to be carried out in indoor environmental chamber. Hopefully through exploring this research project, some useful means can be found to effectively minimize resuspension of indoor deposited particles towards to creating a healthy indoor environment.

空气悬浮颗粒物与人类的健康息息悠关。由空调末端送风射流及人体生理行为如打喷嚏等形成的强烈气流射流以及清扫、擦拭、衣物拍打等活动行为,可以扰动室内气流并致使沉积的颗粒物发生二次悬浮，造成室内可吸入颗粒物含量的上升。这些颗粒物一旦通过呼吸道沉积在肺部，极易使人致病。颗粒物发生二次悬浮是沉积颗粒与其附着表面分离的结果,受重力、附着表面黏附力、以及气流水力作用的共同支配。本课题拟从分析气流射流、表面清扫、及衣物拍打等扰动行为入手，研究其激扰的气流模式、以及由此致使沉积颗粒发生二次悬浮的作用力及能量转换机理。在研究策略上将运用计算流体力学、颗粒动力学、弹性力学建模的方法，从宏观与微观两个层面揭示颗粒在各作用力下从附着面脱离或逐步地由滚动、滑移、直至浮起升空的二次悬浮动力学成因，并辅以环境实验室内各种物理模型试验，试图从揭示颗粒物悬浮所包含的力学机制入手，探索合适的途径抑制空气中悬浮颗粒物的含量。

空气悬浮颗粒物与人类的健康息息悠关。由空调末端送风射流及人体生理行为如打喷嚏等形成的强烈气流射流以及清扫、擦拭、衣物拍打等活动行为,可以扰动室内气流并致使沉积的颗粒物发生二次悬浮，造成室内可吸入颗粒物含量的上升。这些颗粒物一旦通过呼吸道沉积在肺部，极易使人致病。颗粒物发生二次悬浮是沉积颗粒与其附着表面分离的结果，受重力、附着表面黏附力、以及气流水力作用的共同支配。本项目开展了三大块以实验测试为主的研究，包括气流射流激扰颗粒的再悬浮、毛刷拂扫表面激扰沉积颗粒的再悬浮、及击打布料激扰附着颗粒的再悬浮。应用高速相机、流场示踪、以及标准测试粉尘，较为精确测试了各激扰过程的接触表面变形、激扰的气流、颗粒的受力分离过程、粒子的表面去除率、悬浮颗粒的数量等。从流体力学、颗粒动力学、弹性力学的角度，揭示颗粒在各作用力下从附着面分离的动力学成因，探索了抑制或促进颗粒物从表面分离的策略途径。. 研究发现，当射流高度较低时，载颗粒表面受射流冲击的形状为圆盘形，而随着射流高度的增加，射流冲击形状逐渐变为环状。在低积尘密度下，射流激扰致使颗粒从附着表面的分离量随着射流高度的增加而递减。但是在高积尘密度下，则可能呈现颗粒分离量随着射流高度的增加先上升到峰值，然后再递减。最大颗粒分离量的发现，将有助于在工程上选取最佳射流高度，来获得理想的颗粒去除效果。较细的刷毛、较快的清扫速度以及刷毛间较大的分散度都将促进刷毛尖端形成向上运动的漩涡颗粒团，促进颗粒再悬浮，这为实际清扫中减少颗粒扬尘提供了指导。当击打附着在布料上的沉积颗粒时，需要布料达到一定大小的反向加速度才能发生颗粒分离，工程应用时要使击打杆满足加速度的阈值要求。布料振动将激扰周围形成湍流，促进颗粒的脱离，清灰时可设计促使布料持续振动的设备。布料与击打杆接触部分的沉积颗粒去除效果较差。布料拉伸率较大的地方去除效果较好，应用时可对布料进行适当绷紧拉伸处理。