Microplastic (MP) pollution is a critical environmental issue, yet conventional detection methods are too time-consuming for rapid response. To overcome this limitation, this study develops and validates a novel, low-cost optical detection technique for microplastics based on real-time image analysis of light scattering. The proposed normalized scattering index (S_norm) demonstrated high sensitivity, accurately reflecting changes in MP concentration. Its quantitative validity was established through a strong negative correlation (r ≈ -0.96) with UV-vis transmittance and was further corroborated by direct particle counting. This technique enables rapid concentration assessment without complex sample preparation, offering a valuable tool for the on-site evaluation of various MP mitigation technologies.

Unsteady internal flows in cylindrical rotating cavities with varying aspect ratios (AR=2, 6, 10, 18) are investigated using Large Eddy Simulation (LES). To capture realistic transient behavior, time-dependent rotational conditions are imposed, and the velocity fields are decomposed into rotation-induced and turbulence-induced components. The study focuses on the influence of the aspect ratio on flow structures at multiple axial locations. Spectrogram and energy heatmap analyses reveal that the axial velocity is the most sensitive indicator of aspect ratio variations, as it directly reflects the interference of the Ekman layer and secondary circulation originating from the end-walls. The results demonstrate that in low-aspect-ratio cases, the Ekman suction effect dominates the central core, leading to rapid turbulence transition and vortex fragmentation. Conversely, as the aspect ratio increases, the flow exhibits a non-linear stabilization process, eventually developing self-organized axial vortex filaments. This study provides a comprehensive physical interpretation of the transition from wall-dominated to core-independent flow regimes, offering fundamental insights into flow-induced vibrations in rotating systems.

Electrohydrodynamic (EHD) jet printing on insulating substrates is often limited by residual charge accumulation in deposited droplets. In this study, we propose a demonstration of printing on insulated substrate in which paper is mounted on a silicon wafer. A paper-on-silicon-wafer substrate was integrated with syringe pump, high-voltage amplifier, and Cartesian actuator. Upon infiltration into the paper, water-glycerol mixture based ink is electrically grounded through contact with the silicon wafer. Within the cone-jet regime, the most influential parameter on printed pattern resolution was determined among voltage, flow rate, and substrate velocity. Substrate speed was the most influential, varying the line width 0.40 - 6.39 mm over 0.1 - 10.0 mm/s. Based on this finding, we implemented planar image printing by controlling the substrate velocity. These results demonstrate that a paper-on-silicon-wafer substrate can serve as an insulating substrate for EHD jet printing.

Effective water management in proton exchange membrane fuel cells is critical for maintaining stable operation under high current density conditions, and liquid water is typically discharged from the flow channels in three representative patterns: slug, droplet, and liquid film. To comprehensively understand these complex two-phase flows, an objective and data-driven classification method is essential. This study proposes a novel image-based clustering framework combining statistical feature extraction and t-distributed stochastic neighbor embedding to automatically classify water removal patterns. The effect of image preprocessing techniques, including raw, flat-field correction (FFC), and thresholding, was investigated, revealing that FFC preprocessing achieved an exceptional clustering accuracy of 99.84%. Furthermore, a full-factorial feature combination analysis identified image skewness as the most dominant statistical feature. Subsequent optimization based on the Akaike Information Criterion demonstrated that robust clustering accuracy could be maintained using a minimized subset of only 2-3 features, provided skewness was included. The proposed framework not only provides a highly efficient tool for the classification of two-phase flows in PEMFC but also demonstrates significant potential for broader multiphase flow visualization applications across various thermofluidic systems.

This study numerically investigates steady two-dimensional laminar natural convection in a differentially heated square cavity with a bottom-mounted vertical partition, focusing on the effects of the Prandtl number and partition height. Simulations were conducted at Rayleigh numbers of Ra = 10³ and 10⁵ for or the Prandtl number (Pr = 0.71 - 6), with a fixed partition thickness of w = 0.02 and heights of h = 0.1 - 0.7. At Ra = 10³, heat transfer is predominantly conduction-dominated, and variations in the Prandtl number have a negligible influence on the thermal structure and overall heat-transfer behavior. In contrast, at Ra = 10⁵, pronounced Prandtl-number effects emerge due to boundary-layer modification and thermal-field reorganization. Increasing partition height progressively restricts the effective circulation region and suppresses convective heat transfer, leading to a significant reduction in the surface-averaged Nusselt number, exceeding 60% at high partition heights. Correlations for the surface-averaged Nusselt number are proposed to capture the distinct heat-transfer behaviors in both conduction- and convection-dominated regimes.

The interaction between a shock wave emerging from a shock tube and a nearby target depends strongly on the distance from the tube exit. In this study, the near-field discharge of a diaphragm-driven shock wave from a circular shock tube is investigated to determine the maximum effective distance at which a sample can receive the maximum propagating shock energy prior to attenuation. A combined experimental and numerical approach is employed. High-speed shadowgraph imaging captures the transient flow structures, while two-dimensional axisymmetric CFD simulations provide distributions of pressure, density, temperature, and internal energy. The results show that as the shock exits the tube, it diffracts at the lip and expands into the ambient environment, forming a shear layer and a toroidal vortex ring. The maximum pressure and internal energy occur in the compressed region immediately behind the shock front during the early stage of shock emergence. Both experimental and numerical results indicate that the longest distance downstream from the shock tube exit for maximum energy transfer from the driven part is approximately 10 mm, beyond which rapid expansion leads to a significant reduction in pressure and internal energy.

This study investigated how geometric asymmetry alters post-stenotic hemodynamics in mild coronary stenosis under pulsatile flow and whether such differences may provide diagnostic information beyond conventional fractional flow reserve (FFR). Three models with the same 40% diameter reduction were tested: a symmetric Control model and two asymmetric Vulnerable models derived from the baseline geometry by hemisection and opposite lateral mirroring. Particle image velocimetry was used to compare axial velocity fields, separation behavior, jet deflection, and turbulent kinetic energy (TKE). At the peak phase (t / T = 0.41), the Vulnerable models exhibited earlier flow separation, stronger upward jet deflection, thicker recirculation regions, and larger reversed-flow zones than the Control model. These changes enhanced shear-layer interaction and increased TKE downstream of the stenosis. The results suggest that even at the same stenosis severity, geometric asymmetry can significantly modify flow instability and may contribute to larger pressure-drop waveform fluctuations beyond mean-pressure-ratio-based FFR assessment.

An experimental and computational visualization study were conducted on a variable exhaust nozzle of an afterburning turbofan engine for transonic aircraft. Three representative mission profiles (combat air patrol, acceleration, maneuver without afterburner) were selected to design the aerodynamic configurations of the variable nozzle, which were subsequently fabricated as a wind-tunnel model for testing. Supersonic wind-tunnel experiments were performed using the fabricated model, and shock-wave structures were captured through Schlieren visualization. The experimentally observed flow features were compared with the numerical flow-field predictions. Unlike two-dimensional nozzles, the axisymmetric configuration produced a three-dimensional conical shock structure, leading to distinct Schlieren patterns that evolved differently along the flow path. The experimentally observed shock patterns showed good agreement with the numerical results, demonstrating the reliability of the computational approach and the effectiveness of the visualization methodology for analyzing three-dimensional axisymmetric variable-area nozzles under supersonic exit flow conditions.

This study develops self-cleaning glass based on liquid-dielectrophoresis to secure the reliability of autonomous driving optical sensors. Numerical analysis optimized a 50 ㎛ electrode gap to maximize electric field concentration. The fabricated device demonstrated 91.4% transmittance and 0.338 nm(Ra) surface roughness, confirming its optical and physical suitability. Under 350 VRMS, it achieved maximum transport speeds of 86.4 mm/s for conductive(DI water) and 3.32 mm/s for non-conductive(Silicone oil) droplets. Utilizing a 1-second sequential switching control, the effective area was entirely cleaned within 6 seconds without surface pinning. A vehicle front camera demonstration verified that vision algorithm object detection errors caused by contamination were successfully restored after -cleaning. By controlling diverse contaminants on a single platform, this system offers a practical anti-contamination solution for mobility sensors and externally exposed optical devices.

Non-viable cells hinder biological analyses and therapeutic outcomes, requiring gentle and reliable separation. Conventional active methods are precise but often complex and costly, increasing interest in passive microfluidic approaches. Here, we present a label-free microfluidic approach combining osmotic treatment with a trapezoidal spiral microchannel to separate viable and non-viable THP-1 cells. Because the two populations have similar initial diameters (~ 11.5 ㎛), sucrose solutions (10 - 3000 mOsm/kg) were used to induce osmotic size differences. The spiral channel promotes rapid mixing via Dean-flow-induced secondary motion, enabling fast osmotic exposure. Inertial lift and Dean drag forces then focus cells at size-dependent equilibrium positions. Performance was evaluated using 10.7 and 14.5 ㎛ PMMA beads under various flow conditions and validated with THP-1 cells. The system successfully isolated viable cells with a purity of 96.3% and a recovery rate of 95.7%. This study provides design guidelines for biological separation using inertial microfluidic systems.