DISTRIBUTION OF PARTICLES SUSPENDED IN CONVECTIVE FLOW IN DIFFERENTIALLY HEATED CAVITY

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.