Nanoparticle Dynamics in a Viscous Fluid at Small Reynolds Numbers

[Abstract]: \nDynamics of small size solid particles in viscous density stratified fluid is studied analytically and numerically within the framework of the creeping flow approximation corresponding to very small Reynolds numbers. The equation of motion for a particle includes a consideration of the gravity/buoyancy force, Stokes drag force and the Bossinesq–Basset drag (BBD) force. The problem studied is applicable to many practical situations where particle motion may be experienced in viscous fluid of variable density. Exact analytical solutions describing particle motion are obtained both for the buoyant and heavy particles. It is shown that for a non-stationary motion of a particle, the consideration of the BBD force is principally important, resulting in much slower decay of the particle velocity compared to the case when only the Stokes drag force is accounted. A heavy particle motion in piece-homogeneous multilayered fluid and in smoothly stratified fluid is also studied. The results obtained are relevant in particular to the physical processes occurring in the cooling systems of nuclear reactors such as the Open Pool Australian Light-water research reactor OPAL at Lucas Heights, Sydney.