Natural convection of microparticle suspensions in thin enclosures

Natural convection experiments were performed with aluminum oxide microparticle aqueous suspensions in thin enclosures of circular planform at angles of inclination to the horizontal of 90°, 30° and 0°. The average size of the aluminum oxide particles was about 250 nm, and volume fractions of 1.31% and 2.72% were used. The aspect ratio varied from 50.7 to 10.9, and the maximum Raleigh number was 3 × 105. No effect of particles on the Nusselt number–Rayleigh number relation was found for the vertical enclosure at 90°. However at 30° and 0° (horizontal) there was a decrease in Nusselt number compared to pure water, which was pronounced at lower Rayleigh number and higher particle concentrations. This anomalous behavior is attributed to sedimentation.