The Hong Kong Polytechnic University

Efficient internal mixing of colliding droplets upon coalescence is critical to various technological processes such as color-manipulation in ink-jet printing and the initiation of liquid-phase reaction of gelled hypergolic propellants (GHPs) in rocket engines. Recognizing that such processes can be optimized by varying the impact inertia as well as employing fluids of non-Newtonian rheology, the head-on collision, coalescence and internal mixing pattern between two impacting equal-sized droplets of non-Newtonian fluids was computationally investigated by using the lattice Boltzmann method. Results show that, with increasing non-Newtonian effects, droplet deformation and separation following coalescence is promoted for shear-thinning fluids, while permanent coalescence allowing extended duration for mixing is promoted for shear-thickening fluids. Furthermore, large-scale internal mixing is promoted for the colliding droplets with larger shear-thinning disparity, while coalescence and mixing is synergistically facilitated for the collision between a shear-thinning droplet and a shear-thickening droplet. The individual and coupled influences of viscosity on the droplet deformation and impact inertia, internal motion, viscous loss, and merging of the colliding interfaces leading to the observed outcomes were mechanistically identified and described.

 

Dr. Zhang received his Bachelor of Science in Mechanical Engineering from the University of Science and Technology of China and Master of Science in Aerospace Engineering from the Institute of Mechanics, Chinese Academy of Sciences, in 2000 and 2003 respectively. He obtained his PhD in Mechanical and Aerospace Engineering from Princeton University in 2010. Dr. Zhang served as a research staff at the Institute of Mechanics, Chinese Academy of Sciences, from 2003 to 2004. He worked as a Combustion Energy Research Fellow at Princeton University, from 2010 to 2012. Dr. Zhang joined the Department of Mechanical Engineering at The Hong Kong Polytechnic University as Assistant Professor in July 2012. Currently, Dr. Zhang’s main areas of research interests are theoretical and numerical combustion, chemical kinetics, droplet dynamics and rarefied gas dynamics.