Abstract: This is the first part of the investigation on PM_2.5 separation by falling liquid cylinder (FLC)in cross-flow of aerosol contaminated fluid. It is suggested that the mechanism for PM_2.5 separation in this system is due to the particle motion to and absorption by the surface of FLC. The driving forces for particle motion are provided by the velocity field and enhanced by the thermophoretic force originated from the temperature gradient in the gas phase close to the surface of FLC when heat transfer is taking place on the surface. A differential equation is deduced for the particle motion towards the surface of FLC and used to calculate the particle trajectory by inverting integration numerically, through which the maximum moving radius of removable particles can be determined. The distance from the maximum moving radius to the surface of FLC is defined as the separation thickness. The ratio of gas volume flow rate through the separation thickness to that passing the whole area of FLC is defined as PM_2.5 absorption efficiency η_i based on a single FLC. The total separation efficiency of a regularly arranged bundle of FLCs is formulated according to a series-connection model. With the basic parameters of FLC bundle geometry, fluid flow as well as heat and mass transfer, the total separation efficiency can be calculated using the algorithm developed in this paper.A demonstration for the calculation is shown with a practical example with gas flow Re_c=170 in a steady smooth cross-flow.The separation efficiency of a single FLC with a diameter of 4 mm is 1.18%.The total efficiency of a bundle, consisted of 195 FLCs series-connected in row with a total length of 1170 mm, is calculated up to 90%.This is the first part of the investigation on PM_2.5 separation by falling liquid cylinder (FLC)in cross-flow of aerosol contaminated fluid. It is suggested that the mechanism for PM_2.5 separation in this system is due to the particle motion to and absorption by the surface of FLC. The driving forces for particle motion are provided by the velocity field and enhanced by the thermophoretic force originated from the temperature gradient in the gas phase close to the surface of FLC when heat transfer is taking place on the surface. A differential equation is deduced for the particle motion towards the surface of FLC and used to calculate the particle trajectory by inverting integration numerically, through which the maximum moving radius of removable particles can be determined. The distance from the maximum moving radius to the surface of FLC is defined as the separation thickness. The ratio of gas volume flow rate through the separation thickness to that passing the whole area of FLC is defined as PM_2.5 absorption efficiency η_i based on a single FLC. The total separation efficiency of a regularly arranged bundle of FLCs is formulated according to a series-connection model. With the basic parameters of FLC bundle geometry, fluid flow as well as heat and mass transfer, the total separation efficiency can be calculated using the algorithm developed in this paper.A demonstration for the calculation is shown with a practical example with gas flow Re_c=170 in a steady smooth cross-flow.The separation efficiency of a single FLC with a diameter of 4 mm is 1.18%.The total efficiency of a bundle, consisted of 195 FLCs series-connected in row with a total length of 1170 mm, is calculated up to 90%.

Key words: absorption of PM_2.5, falling liquid cylinder in cross-flow, thermophoresis, gas-liquid interface, boundary layer

摘要： 提出了横掠液柱流的速度场和温度场推动PM_2.5微粒附面运动机理，建立了微粒附面运动微分方程和数值积分反演方法，计算粒子运动轨迹并预测可吸收的微粒运动最大分离半径。定义最大分离半径与液柱表面之间附面层的厚度为分离厚度，以气溶胶流体通过该区域的体积流量与横掠单液柱的总体积流量之比代表单液柱吸收效率；热泳推动力是强化吸收效率的主要因素。基于单液柱吸收效率，按串联模型导出规则排列的液柱群整体分离效率计算公式，依据液柱交叉流几何结构、流体流动和气液两相传热传质参数即可确定整体分离效率。对交叉流Reynolds数为170的实例计算显示，直径4 mm的单液柱吸收效率为1.18%，由195排液柱群组成的长度为1170 mm的分离通道整体分离效率达到90%。

关键词: PM_2.5吸收, 液柱交叉流, 热泳, 气液界面, 附面层