This study examined the size and distribution of micro bubbles generated using a venturi nozzle bubble generator and compared them with a high flow rate prediction model. The micro bubble size was evaluated using arithmetic and Sauter mean diameters, while the distributions were analyzed with probability density functions. Experiments involved ejector-type and swirl-type venturi nozzles, capturing bubbles with a 10X microscope. ImageJ software was used for post-processing to extract size and distribution data. Analysis was performed at the air flow rates of 0.04 LPM and the water flow rates of 0.7-1.2 LPM. Bubble production increases with the water flow rate in both nozzle types, but the average diameter has little variation. For the same water flow rate, the swirl-type generates 12 times more bubbles and 19.2% smaller bubbles than the ejector-type. The experimentally measured average bubble diameter exceeded the predicted value under high flow conditions.

Various configurations of a specific ionic liquid-piston compressor were proposed, focusing on the surface area-to-volume ratio. This study comprehensively analyzed the heat transfer characteristics of working fluids within the cylindrical chamber during the compression process. Furthermore, a detailed evaluation was performed on the thermal and compression efficiency of the whole system. The optimal design, configuration 1, characterized by a surface area-to-volume ratio of 0.1, yielded the highest thermal performance at 57.6% and an impressive compression efficiency of 97.9%. As the surface area-to-volume ratio increased, the duration of the compression process was extended, leading to enhanced heat transfer between the hydrogen and the surrounding environment. This resulted in improved overall system efficiency.

An experimental study was conducted to investigate the effects of bio-inspired convergent-divergent (C-D) riblets on the flow field behind a 35-degree slanted-back Ahmed body. Various measurements were taken at a Reynolds number of Re = 1.48×10⁴. The results demonstrated the lower recirculation zone behind the Ahmed body with C-D riblets was smaller compared to the smooth model. Besides, the upper recirculation zone moved down vertically and shifted to the upstream with C-D riblets. The maximum Reynolds Shear Stress in the lower recirculation region decreased for the Ahmed body with a roughened upper surface by C-D riblets. Power spectrum analysis conducted at various points revealed that the application of C-D riblets has increased the dominant frequency peak in the wake while reducing the power spectrum values at all measurement points. The Proper Orthogonal Decomposition analysis indicated that the surface roughness contributed to a reduction in the energy of the first two modes.

To analyze the flow and noise characteristics of a positive displacement hydrogen compressor, a computational fluid dynamics (CFD) simulation based on the Lattice-Boltzmann Method (LBM) was performed. For detailed analysis the discharge flow of the compressor was divided into three regions: the area around the valve, the discharge jacket, and the outlet pipe. Hydrogen passing through the valve formed turbulent jets, which induced high-frequency noise. Inside the discharge jacket, changes in the cross-sectional area caused continuous variations in the average velocity and turbulence characteristics. In the outlet pipe with an elbow, high flow velocity corresponding to the relatively narrow cross-section was observed. Additionally, flow separation occurring on the inner corner of the elbow enhanced turbulence, contributing to the amplification of high-frequency noise. This study provides a physical understanding of the flow and noise issues in positive displacement hydrogen compressors and presents a fundamental analysis to support the design of efficient and low-noise compressors.

Today, hydrogen, known as a clean energy, is considered a promising alternative energy source for achieving carbon neutrality. This requires an analysis method for the combustion characteristics of hydrogen-blended-fuels at actual combustor operating conditions. The purpose of this study is to investigate premixed laminar flames of hydrogen-blended-fuels in an atmospheric condition. Computational Fluid Dynamics(CFD) with Gas Research Institute(GRI)-Mech 3.0 was used to simulate a laminar premixed flame in a Bunsen burner. Comparative validation was performed with flame visualization images at the same combustion conditions. The visualization of OH radicals confirmed that the concentration of OH radicals increases with the hydrogen blended ratio, resulting in an enhanced flame velocity. Under lean combustion conditions, OH radicals are predominantly concentrated at the reaction boundary due to the limited availability of fuel components, leading to a narrower combustion area. Under rich combustion conditions, the combustion area expanded as OH radicals are produced through additional reactions with atmospheric oxygen. The interpretation of the thermal interaction between the flame and the combustor is important to predict the flame shape and flashback. This numerical method will be a means of providing various data on hydrogen as a combustion material for the commercialization of hydrogen.

This study investigates the capture of rod-shaped particles by raindrops through vertical wind tunnel experiments. In contrast to past studies that focused on spherical particles, we examine the interactions between rod-shaped particles and falling droplets, a more accurate representation of real-world conditions where irregularly shaped particles, such as microplastics and volcanic ash, are prevalent. A novel shadowgraph imaging technique is employed to track the three-dimensional movement of the rod-shaped particles. The findings reveal that the particle’s alignment and impact location play a critical role in determining whether it is captured or escapes. Particles with a low elevation angle or a wide azimuth angle are more likely to be captured due to a larger contact area with the droplet, resulting in a greater loss of momentum. These results underscore the distinct capture behaviors of rod-shaped particles, providing new insights into atmospheric particle removal processes via precipitation.

Solid Oxide Fuel Cells (SOFCs) operate continuously at high temperatures ranging from 600-1000℃, which increases the risk of failure due to thermal stress concentration, particularly at the corners. Therefore, optimizing the flow channel design is essential to achieve uniform temperature distribution, enhance corner cooling, and maximize power output. To address these challenges, a conventional Cross-flow model and three newly designed models with four divided flow channels were compared using computational fluid dynamics (CFD) simulations. Performance was evaluated by monitoring flow distribution, power density, and electrolyte temperature distribution. The Cross-flow model exhibited high flow uniformity, leading to high power density. However, it also showed asymmetric temperature distribution and a wide temperature range, which can accelerate degradation. To mitigate these issues, three novel quarter-divided flow path designs-Quarter L-pin, Quarter X, and Quarter X-pin-were proposed. Simulation results demonstrated that the two pin-channel models achieved high power density and low pressure drop due to larger reaction areas and increased flow direction flexibility. Among the three models, the Quarter L-pin model exhibited the narrowest temperature range. The Quarter X and Quarter X-pin models showed superior corner cooling performance, with the Quarter X-pin model achieving the lowest corner temperature among all configurations. In extreme operating conditions of SOFCs, optimizing temperature distribution is critical. This study provides valuable insights into minimizing power density losses while enhancing durability and lifespan in SOFC design.