Visualization and PTV Study of Natural Convection in Particle Suspensions. Simultaneous Measurements of Velocity, Temperature and Interface between Particle-Free Fluid and Suspension.

Abstract

Natural convection in a suspension was studied experimentally using both refractive index matching and laser induced fluorescence (LIF) techniques. A rectangular test section was filled with particle suspension and was heated from a horizontal bottom, and two facing vertical walls were kept at a constant temperature. The images of the fluorescent particles were captured by a CCD camera through a sharp cut filter which separates emitted fluorescence from scattered excitation light. The flow velocity fields were analyzed quantitatively using Particle Tracking Velocimetry (PTV). Interface between particle-free fluid and suspension as well as temperature fields was visualized simultaneously with the velocity fields. It was suggested that two-layer convection cells were driven by both heating and sedimentation of particles which drives convection in the overlying layer due to the release of the heated clear fluid at the interface.