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Our aim is to explore, both experimentally and theoretically, the cumulative 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 main flow structure in such a cavity consists in one or two spiraling motions. Long-term observations of such structures with the help of tracers ͑small particles͒ indicated that accumulation of the particles may set in at some flow regions. For theoretical insight into the phenomenon, a simple analytical model of recirculating ͑rotating͒ flow was studied. 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 density difference are of importance. Besides buoyancy, the effects of Saffman's force and the inertial forces are also taken into account when calculating particle trajectories. Both cases were analyzed, particles with density slightly higher and lower than the fluid. It was found that in our case the inertial forces are negligible. In the numerical experiment trajectories of particles were investigated. The particles were 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 convective cell was explored. In the model-analytical study of a simple spiraling motion, it was found that due to the interaction of the recirculating convective flow field and the gravity-buoyancy force, the particles may be trapped in some flow regions, whereas the rest of the flow field becomes particle-free. This prediction agrees fairly well with the numerical and experimental findings.

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