Self-Organization of Convective Flows and a Cluster of TiO2 Particles in a Water Film under Local Heating: Interaction of Structures at Micro- and Macrolevels

Self-organization of both convective hexoganal cells and a cluster of particles in a liquid under local laser heating of a water film is experimentally studied. The interaction of thermocapillary and thermogravitational free convection changes the flow patterns and the cluster structure. The cluster of agglomerates (the diameter of agglomerates is 80-100 mu m) consists of particles with a diameter of 1-2 mu m. The sizes of the entire cluster and agglomerates, as well as the number of cells, change cyclically over time. Hexagonal convective cells have a very small size (about 60-100 mu m), which is almost an order of magnitude less than the height of the liquid film. Several characteristic convective scales are implemented in the range of 60 mu m-20 mm. The observed macrostructure of the convective flow inside the film is determined by the complex nonlinear interaction of vortices of different scales. Instead of an obvious toroid, there are two contacting vortices of the averaged flow. The contact line of the vortices has a random orientation for different experiments. The value of the average integral convection scale can be used to predict the average velocity of convection in a film.