Study on short time dynamics of liquid droplet spreading on smooth and coated surface

• Main Author: Seoh, Kelvin Jin Wei
• Other Authors: Tran Anh Tuan
• Format: Final Year Project
• Language: English
• Published: 2018
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics
• Online Access: http://hdl.handle.net/10356/74734
• Institution: Nanyang Technological University

Aqueous sodium chloride solution is used as the droplet to study the regimes of low viscosity liquid spreading on a smooth surface. Liquid spreading has been studied extensively using high-speed imaging to measure the spreading radius. Literature review was done on the theories behind liquid spreading, obstacles faced by other researchers when performing high-speed imaging, the scaling of spreading radius with time and the effects of varying other parameters such as viscosity, surface wettability and drop size. The review was also done to find inspiration to innovate the experimental method in measuring radius of spread as well as to improve the collection experimental data. Besides the conventional combination of bottom and side high-speed imaging method, an electrical approach is introduced for this experiment to improve the experimental results produced by the optical method up to four decades faster in term of time measurement. The spreading radius of the droplet is found by connecting the spreading region to a Wheatstone bridge circuit where the unknown impedance of the experimental region is measured and converted to radius with regards to time. The results are then combined with that of optical method to show that both methods can complement each other. The spreading is observed to start in a viscous regime before transition to an inertial regime, which also shows that this new approach in studying the liquid spreading on a smooth substrate is viable. In addition, the initial spreading pattern is observed to be comparable to coalescence of two droplets of the same solution in air.