강인석 교수

The drag coefficient CD=48/R for a spherical bubble in a uniform streaming flow at high Reynolds number, which was first obtained via a dissipation method by Levich [Zh. Eksp. Teor. Fiz. 19, 18 (1949)], is rederived here by direct integration of the normal stress over the bubble surface. The present study also shows that the drag coefficient up to O(R−1) depends only on the O(1) vorticity distribution right on the bubble surface, and is independent of the vorticity distribution in the fluid. The

A brief description of a numerical technique suitable for solving axisymmetric, unsteady free-boundary problems in fluid mechanics is presented. The technique is based on a finite-difference solution of the equations of motion on a moving orthogonal curvilinear coordinate system, which is constructed numerically and adjusted to fit the boundary shape at any time. The initial value problem is solved using a fully implicit first-order backward time differencing scheme in order to insure numerical

This study investigates the effects of drop size and viscosity on spreading dynamics, including response time, maximum velocity, and spreading pattern transition, in response to various DC voltages, based on both experiment and theoretical modeling. It is experimentally found that both switching time (i.e., time to reach maximum wetted radius) and settling time (i.e., time to reach equilibrium radius) are proportional to 1.5th power of the effective base radius. It is also found that the maximum

The dynamics and breakup of a bubble in an axisymmetric, time-periodic straining flow has been investigated via analysis of an approximate dynamic model and also by time-dependent numerical solutions of the full fluid mechanics problem. The analyses reveal that in the neighbourhood of a stable steady solution, an $O(\epsilon^{\frac{1}{3}})$ time-dependent change of bubble shape can be obtained from an O (ε) resonant forcing. Furthermore, the probability of bubble breakup at subcritical Weber num

A digital microfluidic system based on a direct electric charging and subsequent electrophoretic manipulation of droplets is made by simple fabrication at low cost. Digitally controlled two-dimensional droplet motions are realized by digital polarity control of an array of electrodes. By independent control of droplets and colorimetric detection, the coalescence and mixing of droplets is analyzed quantitatively. The gelation of sodium alginate and the crystallization of calcium carbonate by mult

Complex coacervation is a liquid-liquid phase separation in a colloidal system of two oppositely charged polyelectrolytes or colloids. The interfacial tension of the coacervate phase is the key parameter for micelle formation and interactions with the encapsulating material. However, the relationship between interfacial tensions and various salt solutions is poorly understood in complex coacervation. In the present work, the complex coacervate dynamics of recombinant mussel adhesive protein (MAP

The method of domain perturbations is used to study the problem of a nearly spherical bubble in an inviscid, axisymmetric straining flow. Steady-state shapes and axisymmetric oscillatory motions are considered. The steady-state solutions suggest the existence of a limit point at a critical Weber number, beyond which no solution exists on the steady-state solution branch which includes the spherical equilibrium state in the absence of flow (e.g. the critical value of 1.73 is estimated from the th

Numerical solutions of the full Navier–Stokes equations are used to investigate the steady and unsteady deformation of a bubble in a biaxial straining flow for Reynolds numbers in the range 0≤R≤400, and Weber numbers up to O(10). The steady-state bubble shape and the frequency of small amplitude oscillations of shape are both identical for biaxial and uniaxial straining flows in the potential flow limit. However, for a large, but finite Reynolds number, the bubble shape in the biaxial straining