Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.
This work is devoted to comparison of changes in geometry and in light transmittance of evaporating drop of nanocolloid deposited on flat surface. One of the focuses of paper is aimed at differentiation of drying process into separate stages, each being characterized by particular behavior of suspension nanoparticles inside the droplet, the last of which ends by forming of ring-shaped patterns (known as “coffee ring effect”) that appear after all the fluid has evaporated. Dynamics of colloids` evaporation was studied according to two observing techniques. The first one was based on spectrometric measuring of light transmitted through droplets. The second method was based on registering of geometrical properties of drying puddles that were changing in time due to evaporation. Patterns left by droplets of nanocolloids were alike in general – collars were formed along the perimeter of initial droplet. According to coffee ring effect a major part of suspended particles assembled in these collars though a thin film of suspended substance deposited within initial drop perimeter. The results of drying dynamics experiments carried out in two different techniques appeared to be also different. The second (geometrical) method showed a uniform decrease of drop height while the first (spectrometric) method showed non-uniform changing of parameters. The time of drying according to the second technique was less than the time of drying received in experiments undertaken with the first technique.
