With increasingly stringent emissions legislation, such as that stipulated by the International Maritime Organization, for nitrogen oxide emission reduction in marine diesel engines, the imperative of curtailing nitrogen oxide emissions from marine diesel engines is intensifying. Consequently, the significance of aftertreatment technologies, including diesel particulate filters (DPFs) and selective catalytic reduction (SCR), is poised to grow substantially. In particular, a redesign is required to reduce the size of DPF and SCR systems for application in small ships. In this study, we varied the shape of the filters in DPF and SCR systems, aiming to achieve a distinct flow pattern and enable overall miniaturization. The performance metrics, including the nitric oxide (NO) reduction rate, NH₃ slip rate, and pressure drop, of the redesigned models were compared with those of the conventional model. Computational fluid dynamics simulations were used to compare the performance of the redesigned model with that of the conventional model in terms of NO reduction and pressure drop. The redesigned system achieved a NO reduction rate of 6.9% below that of the conventional system, offering additional noteworthy benefits such as a 50% reduction in both pressure and overall length.

This study addresses the challenges of and opportunities for achieving the ambitious greenhouse gas emissions reduction target of the fishery sector of the Republic of Korea, set at 96% by 2030. We also focus on the current status of land-based aquaculture and underground seawater resource development, quantitatively compare energy inputs for land-based fish cultivation, and evaluate the potential of underground seawater to reduce CO₂ emissions. Since 2010, 762 underground seawater boreholes have been developed, yielding a cumulative daily pumpage of 125,780 m³. Jeollanam-do was found to have the highest daily pumpage, with an annual energy requirement of 131,205,613 Mcal. Despite the fact that the energy demands for underground seawater are higher in some months, it provides a 22.6% reduction in total annual energy consumption compared to surface water. The use of underground seawater for heating or cooling resulted in a 24.1% reduction in the required input energy. However, energy requirements increase due to the relatively high surface water temperature in some regions and seasons. This study also highlights the utilization of underground seawater in heating or cooling surface water via indirect applications using geothermal heat pumps. This innovative research broadens the methods of greenhouse gas mitigation, particularly in the agriculture, livestock, and fisheries industries.

Hydrocyclones are widely used for solid–liquid separation, but their performance is highly sensitive to the geometric design. Previous studies often focused on individual structural parameters; however, the combined effects of the vortex finder diameter and aspect ratios on the internal flow field and particle separation behavior remain insufficiently clarified. This study conducted three-dimensional numerical simulations using the realizable k-ε turbulence model, combined with the discrete phase model. The particle size distribution behaves according to the Rosin–Rammler function. Seven different geometries were evaluated under identical operating conditions to systematically investigate how the diameter and aspect ratios influence the internal vortex structures and separation behavior. A decrease in the diameter ratio enhances the dominance of the outward centrifugal forces, which increases the downward discharge of coarse particles but also results in greater liquid entrainment through the underflow. Conversely, larger diameter ratios strengthen the secondary vortex and promote upward flow. However, this also leads to decreased recovery of fine particles due to weakened centrifugal action. Adjusting the aspect ratio effectively mitigates these tradeoffs. Increasing the cone length enhances the residence time, stabilizes the upward vortex, and improves the separation of fine particles. Although the overall separation performance shows diminishing returns beyond a certain aspect-ratio threshold, the recovery of fine particles continues to improve. The results reveal that a balance between centrifugal and drag forces is essential, which is achieved through coordinated control of the vortex finder diameter and cone geometry. This balance is critical for maintaining stable flow fields and high efficiency in fine-particle removal. The findings provide practical design guidance for hydrocyclones, particularly in applications that require enhanced recovery of fine particles and stable multiphase flow behavior.