Our aim is to explore, both experimentally and theoretically, the cumu
lative effects of small particle-liquid density difference, where the
particles are used as tracers in recirculating flow. As an example we
take a flow field generated in a differentially heated cavity. The mai
n flow structure in such a cavity consists in one or two spiraling mot
ions. Long-term observations of such structures with the help of trace
rs (small particles) indicated that accumulation of the particles may
set in at some flow regions. For theoretical insight into the phenomen
on, a simple analytical model of recirculating (rotating) flow was stu
died. It was assumed that particles are spherical and rigid, and their
presence does not affect the flow field. The particle Reynolds number
is negligibly small, hence only the effects of particle-liquid densit
y difference are of importance. Besides buoyancy, the effects of Saffm
an's force and the inertial forces are also taken into account when ca
lculating particle trajectories. Both cases were analyzed, particles w
ith density slightly higher and lower than the fluid. It was found tha
t in our case the inertial forces are negligible. In the numerical exp
eriment trajectories of particles were investigated. The particles wer
e allocated at random in the flow field obtained by numerical solution
of the natural convection in the differentially heated cavity. In the
experimental part, behavior of a dilute particle suspension in the co
nvective cell was explored. In the model-analytical study of a simple
spiraling motion, it was found that due to the interaction of the reci
rculating convective flow field and the gravity-buoyancy force, the pa
rticles may be trapped in some flow regions, whereas the rest of the f
low field becomes particle-free. This prediction agrees fairly well wi
th the numerical and experimental findings. (C) 1996 American Institut
e of Physics.