Experimental studies on transient features of natural convection in particles suspensions

Particle Tracking Velocimetry (PTV), in conjunction with the refractive index matching technique and laser induced fluorescent (LIF) tracer particles, was used to overcome the visualization problem in a particle suspension. A square test section was filled with the particle suspension and impulsively heated from the bottom wall while the two facing vertical walls were kept at a constant temperature. The two-dimensional velocity fields, particle distributions in a plane and the wall temperature fields were visualized simultaneously using three cameras. The results showed peculiar flow patterns such as the formation and vanishing of two-layer convection cells which were distinct from those in a clear, particle-free fluid. Sedimentation driven convection is thought to be the fundamental mechanism for the formation of these two layer convection cells. The overlying particle-free-layer convection was started by the release of the heated clear fluid at the interface between the particle-free layer and the suspension.