关键词: PM_2.5吸收, 液柱交叉流, 热泳, 气液界面, 附面层

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