Evaporation of sessile saline nanofluid droplets

The objective of this experiment is to study the effects of sodium chloride (NaCl) and the Aluminum oxide nanoparticles on the evaporation process of the sessile droplet. Much attention now has been attracted in the control of the dried patterns of an evaporated sessile droplet, which are driven by application such as ink-jet printing, bio-deposition, micro-coating, disease diagnosis, etc. The experiment was carried out on silicon wafer with varying concentration of NaCl and Aluminum oxide nanoparticles. The variation of the diameter and contact angle of the droplet with time were measured and the profile and pattern of crystallization were analyzed. For the evaporation of saline nanofluid droplet, the increasing of NaCl concentration will cause an increase in the initial contact angle while the variation of nanoparticles concentration seems to have little effect on the evaporation process. The final drying patterns show that, the evaporation of saline droplet tend to form one big crystal. While if there are also 〖Al〗_2 O_3 nanoparticles in the droplet solution, a coffee-ring stain along with several smaller NaCl crystals near the droplet edge was formed. As the concentration of NaCl increases, the size of the NaCl crystal also increases. However, the number of crystals at the rim of the droplet decreases. Future study can focus on the inner vortex flow during the evaporation of the saline nanofluid droplet, exploring the detailed structure and the effects on the final drying patterns.Bachelor of Engineering (Mechanical Engineering