Horizontal gravity separators are important components in the production of unconventional petroleum resources. While tremendous efforts have made on the sizing of separators, relatively few studies have addressed their operational performance under varying outlet conditions. This study aims to investigate the effect of water outlet pressure on the performance of the separator to establish guidelines for its proper operation. Three-dimensional computational fluid dynamics (CFD) simulations are conducted using the Eulerian multiphase model and interfacial concentration area. Four water outlet pressures ranging from 7537.2 to 7421.9 Pa are examined under fixed inlet flow rates. The numerical method is validated by comparing it with experimental results. The numerical results confirm that the separation efficiency improves as the water outlet pressure decreases primarily due to the increased thickness of the oil pad. Notably, the analysis reveals that meeting residence time criteria alone does not guarantee high separation performance, as outlet pressure significantly affects fluid distribution and phase separation. These findings suggest that maintaining the water outlet pressure below 7448.5 Pa is essential for achieving efficient separation in practical operations.

In South Korea, securing ground space for installing hydrogen refueling stations in urban areas is challenging due to limited ground space and high-density development. Safety concerns for hydrogen systems in enclosed urban environments also require careful consideration. To address this issue, this study explored a method of undergrounding hydrogen infrastructure as a solution for urban hydrogen charging stations. This study examined the characteristics of hydrogen diffusion and concentration reduction under leakage conditions within a confined hydrogen infrastructure, focusing on key safety systems, including emergency shut-off valves (ESVs) and ventilation fans. We discovered that the ESV reduced hydrogen concentration by over 80%. Installing two or more ventilation fans arranged horizontally improves airflow and enhances ventilation efficiency. Moreover, increasing the number of fans reduces stagnant zones within the space, effectively lowering the average hydrogen concentration.

This study aims to establish a foundation for developing a ventilation system to address potential hydrogen leakages in underground equipment. The dimensions of this space are 4.2 × 2.2 × 2.2 m³. It features main and auxiliary inflow vents and fan outflow vents. Using the commercial software ANSYS Fluent, a three-dimensional transient RANS is performed to analyze hydrogen diffusion phenomena during a leakage using mass, momentum, and species-conservation equations. The study obtains numerical analysis results by varying the number of fans, open/closed state of the main inflow vent, leakage nozzle diameter, and leakage flow rate. In addition, the study examines the spatial distribution of hydrogen concentration within the room and its temporal variations at various points. The ventilation performances for different scenarios are compared and an effective ventilation method is discussed. Additionally, this study proposes the simple model to predict the volume-averaged hydrogen concentration over time and evaluates it by comparing with numerical results. The simple model effectively predicts the trend of the volume-averaged hydrogen concentration, and reasonably predicts the time at which the volume-averaged hydrogen concentration attains 1 and 4 vol%.