Dean fluid flow offers many advantages to the separation of small-sized particles, compared to existing microfluidic techniques. For broad applications in various science and engineering fields, this study theoretically and numerically evaluates the trajectory variation of particles by the Dean fluid flow and based on the evaluations, proposes the strategies to improve the accuracy and precision of the particle separation. First, we derived the theoretical equation of the particle separation distance produced by Dean fluid flow in a curved microchannel and validated it through computational fluid dynamics simulation. Further, a parametric study was conducted to explore key parameters to increase the distance between the separated particles and maintain the uniformity of the separation distance till reaching the channel outlet. The results of this study will make a significant contribution to enhancing the efficiency of particle separation by the Dean fluid flow in curved microchannels.

Subsonic wind tunnels play a crucial role in evaluating aerodynamic performance and validating designs across various industries, including aviation, automotive engineering, and architecture. This study presents the design and implementation of a particle image velocimetry (PIV) system to assess the reliability of the subsonic wind tunnel at Hanyang University, which was installed in 2001. The wind tunnel, capable of reaching flow velocities up to 60 m/s, features a complex inlet geometry that necessitates a thorough evaluation of its flow quality. Potential issues such as high turbulence intensity and flow non-uniformity are analyzed using a non-intrusive, high-resolution PIV system. This paper provides a detailed account of the system's design and implementation, highlighting its effectiveness in diagnosing flow characteristics and its potential applications across diverse research fields.

Interaction between a droplet and a heated rotating surface occurs in a variety of industrial applications such as spray cooling systems. We investigate the spreading and movement characteristics of the impacting droplet on a heated rotating surface by adjusting the droplet impacting velocity, droplet diameter, substrate surface movement velocity, and the substrate surface temperature. It is shown that the spreading behavior of the droplet drastically changes as the droplet detaches from the surface when the surface temperature exceeds the Leidenfrost temperature. Meanwhile, above the Leidenfrost temperature, the droplet retains a spheroidal shape and represents a peculiar bulk movement above the rotating surface.

In liquid hydrogen (LH2) fuel tanks, sloshing induced by driving conditions increases LH2 evaporation, reducing storage efficiency. This study conducts numerical simulations to investigate sloshing-induced evaporation in an LH2 tank subjected to constant wall heat flux. We observe that sloshing leads to the formation of a high-temperature area near the tank's side walls, accompanied by the development of an LH2 film. This thin LH2 film maintains direct contact with the heated walls during sloshing, causing significant evaporation. To suppress the formation of the LH2 film, rib structures are installed on both side walls. These rib structures reduce the flow length of the LH2 film along the wall by 31.8%, thereby decreasing the peak evaporation rate by 30.9%. Consequently, cumulative evaporation over a 20-second period is reduced by 10.3%. These results demonstrate that integrating rib structures into liquid hydrogen fuel tanks effectively mitigates sloshing-induced evaporation.

This study experimentally investigates the flame stability and structure of a non-premixed high-swirl combustor fueled with NH₃-H₂ and NH₃-CH₄ mixtures. Power density ranged from 1.5 to 8 MW/m³, aligning with micro gas turbine scales, was investigated for the experiments. Lean blowout (LBO) limits, residence time, and momentum ratio were examined to assess stability characteristics. Flame visualization using OH and NH₂ chemiluminescence revealed that even under lean conditions (φ = 0.37), flame was maintained near the nozzle due to strong recirculation, contrary to typical blowout trends. OH signals indicated compact and persistent reaction zones, while NH₂ emissions highlighted rich-fuel regions. The results demonstrate that swirl-induced recirculation and hydrogen blending enhance flame stabilization under ultra-lean conditions, providing insights for future ammonia-based low-NOx combustion systems.

The motion and wake structure of a freely rising two-dimensional cylinder with a density ratio (the ratio of the cylinder density to the fluid density) of 0.195 were investigated experimentally in a quiescent fluid. The cylinder exhibited a periodic zigzag trajectory characterized by repeated cusp-like points where the instantaneous velocity reached a local minimum. Flow field measurements revealed that, during deceleration, the shear layer developed along the rear surface and remained attached to the cylinder, resulting in an increase in the vortex force. After passing each cusp, the shear layer underwent stretching, splitting, and shedding, which caused the formation and detachment of roll-up vortices and led to a decrease in the vortex force. The alternation between acceleration and deceleration phases was closely associated with changes in the wake structure and unsteady hydrodynamic forces acting on the cylinder.

Plasma, in which many biomarker molecules are suspended, is essential for early diagnosis and medical treatments for various diseases. While blood cells can be easily removed by centrifugation, platelet removal from plasma is comparably difficult due to small size and density similar to plasma. As platelets in plasma may interfere with detection systems, platelet removal is required for precise diagnostics. Here, we propose an elasto-inertial microfluidic device for efficient removal of platelets to separate pure plasma. Based on a co-flow of Newtonian and viscoelastic fluids, we utilize both inertial and elastic forces to translocate the platelets across the co-flow interface for pure plasma separation in a high-throughput, dilution-free manner. We carefully designed the microchannel based on theoretical and numerical analysis and experimentally demonstrated high-purity plasma separation with impurity < 7%. We expect that the proposed method serves as a promising approach for plasma separation for various clinical applications.

This experimental study was conducted to evaluate and compare the characteristics of non-cavitating and cavitating flow fields under identical Reynolds number conditions. Using a circular cylinder, the internal pressure of the cavitation tunnel was adjusted to vary the cavitation number under the same velocity conditions, thereby creating non-cavitating and cavitating flow fields. The wake flow was measured using Particle Image Velocimetry (PIV). The vortex structures, which were symmetric about the centerline of the flow field, were evaluated based on the streamlines of the mean flow field, and the locations of the recirculation regions were compared. A comparison of the velocity components showed that the horizontal and vertical velocity components, u/U and v/U, had smaller values in the cavitating flow field, and the point where u/U recovered to positive values appeared closer to the cylinder. Under non-cavitating conditions, the non-dimensional vorticity remained relatively constant, whereas under cavitating conditions, the non-dimensional vorticity tended to decrease as cavitation developed, with an 11% reduction observed along the centerline.