Boundary effects on creeping motion of an aerosol particle in a non-concentric pore

The boundary effect on translational and rotational mobility coefficients of creeping motion of a spherical aerosol particle in a non-concentric spherical pore is investigated. Both particle and pore surfaces can be frictionally slippery and the particle can be situated at an arbitrary location within the pore. The creeping motion of the aerosol particle is decomposed into two independent components, one parallel with the line of centers of the particle and the pore and the other perpendicular to the line of centers. The parallel and perpendicular components of translational (M-= and M+) and rotational mobility (N- and N+) coefficients are thoroughly studied as functions of normalized particle size (a/b), normalized deviation of the particle center from the pore center (d/b), and normalized frictional slip coefficients of both particle (C-m(*)) and pore ((C) over cap (*)(m)) surfaces. Generally, the presence of the pore surfaces tends to retard the particle motion and results in mobility coefficients smaller than unity. There however exist situations in which the mobility coefficients can go higher than unity, signifying a positive boundary surface effect. This positive boundary effect apparently arises from the slippage between surrounding gas and the boundary surfaces, and is found to occur for M+,N-= and N- at a high enough frictional slip coefficient at a non-zero d/b. The presence of pore surface also induces torque and force for particles translating and rotating, respectively, in the direction perpendicular to the line of centers at a non-zero d/b. The induced mobility function is found to increase moderately with increasing slip coefficient, but decrease sharply with increasing d/b and a/b. (C) 2001 Elsevier Science Ltd. All rights reserved.