摘要
为了对地铁颗粒物进行数值模拟,讨论了不同粒径颗粒物的密度均值,重点分析了地铁颗粒物在区间隧道内运动的受力情况,计算和对比了各主要作用力。结果表明,地铁颗粒物的密度随粒径变化较大,采用平均值表示更为合适,其中PM1、PM2.5和PM10的密度均值分别为2.562 g/cm^3、3.766 g/cm^3和4.043 g/cm^3。由于地铁颗粒物独特的密度属性及区间隧道内特殊的流场环境,颗粒受力情况不能一概而论,当颗粒粒径为1μm时,主要作用力呈现明显的分化,仅需考虑Brownian力和曳力;当颗粒粒径为2.5μm时,重力占据了足够的份额而不能被忽略,需要考虑Brownian力、曳力和重力;当颗粒粒径为10μm时,Saffman力明显增大而不能被忽略,因此需要考虑Brownian力、曳力、重力和Saffman力。
The paper is devoted to providing a theoretical basis and a scientific evidence for the numerical simulation we have conducted on the subway particle pollution, with their mean density and sizes of such particles being in a range of diameters of 1 μm, 2. 5 μm and 10 μm on the basis of the elemental compositions, such as those of Fe, metallic elements and non-metallic elements. However, what we would like to stress is to do an emphatic discussion of the force condition of the subway particles in the tunnel in combination with their flowing field, the fluid density, the viscosity, temperature and the velocity gradient being included. And, in so doing, specific stress has been put on their calculation and detailed comparison. Thus, the final results of our calculation and discussion indicate that the density range of the subway particles in the case of Shanghai stands among 4 - 4. 9 g/cm3, which is slightly smaller than those of the so-far known foreign ones among 3.4 - 4. 7 g/cm3. Therefore, it turns out to be proper to choose the mean sizes as the representative ones, and, in turn, we prefer to take the mean densities for the subway particles as 1 p^m, 2. 5 μm and 10 μm, which are equal to 2. 562 g/cm3, 3. 766 g/cm3 and 4. 043 g/cm3, respectively. On the other hand, the forces acting on the particles are supposed to be classified into two categories, say, the secondary force and the main force. Of the two, the secondary force is supposed to include the b.asset force, the virtual mass force, the thermophoretic force, the pressure gradient force and the Magnus lift force, which can all be neglected, for in the flowing field environment of the tunnel and their density attribute of the subway particles, their main forces tend to vary with the difference of the particle diame- ters. When the diameter of such particles is just 1μm, their divergences can be obvious among the main forces. And, in comparison, the Brownian force and the drag force should be taken as rather large and as large as to the magnitude orders of 10 is and 10TM , whereas the size of the gravity and Saffman force should be taken to be rather small, say, at the level of 10~TM and 10-15, hence, their gravity and Saffman force can then be neglected. Thus, it is only the Brownian force and the drag force that should be taken into consideration. What is more, the diameter of 2. 5μm, the Brownian force and the drag force should be put into the range of the most critical forces. And, so, it should never be ignored or negligent if the ratio of gravity has been big enough as to 2.063%. Thus, it is only necessary to take into account the Brownian force, the drag force and the gravity in the aforementioned cases. Furthermore, when the diameter is 10 μm, the greatest＇force, whose gravity is at the magnitude of 10-13. Drag force which has a proportion of 36. 36% is smaller than the gravity, while Brownian force is smaller than the former two. The strength of Saffman force has extremely transcended that in diameter 1 μm and 2. 5 μm, which cannot be ignored easily. Thus, all the main forces, including Brownian force, drag force, gravity should all be taken into consideration. Besides, Saffman force in the main flowing region and the force in the boundary layer should be considered separately and specifically according to the corresponding regions wherein the particles of 10 μm are situated.
出处
《安全与环境学报》
CAS
CSCD
北大核心
2018年第1期310-314,共5页
Journal of Safety and Environment
关键词
环境工程学
地铁颗粒物
区间隧道
密度均值
受力情况
environmental engineering
subway particles
underground tunnel
mean density values
force condition
