###### Abstract  
Recent advancements in hydrogen tank technology have favored the use of composites over metals for weight reduction, although at the cost of a narrower operating temperature range. Therefore, this study aims to establish safety standards for charging tube skids--large tanks positioned vertically within hydrogen transport vehicles--by examining the variations in temperature distribution under different charging environments through numerical analysis. A two-dimensional axisymmetric model was developed based on ANSYS Fluent to incorporate the effect of buoyancy by applying gravitational conditions along the axial direction. The study analyzed the impact of various charging and environmental conditions (charging time (0-240 min), inlet temperature, ambient temperature, initial temperature (\(-20\)\({}^{\circ}\)C\(\sim\)40\({}^{\circ}\)C), and initial pressure (5-20 bar)) on temperature distribution, ultimately deriving a regression equation to predict the tank's maximum temperature. The findings indicate that the initial temperature has the most significant correlation with the tank's temperature, followed by charging time and ambient temperature. Inlet temperature and initial pressure demonstrated minimal influence within the study's scope. The derivation of predictive formulas for the maximum temperatures of the tank's three regions, all showing an R\({}^{2}\) value of 0.99 or higher, highlights the practicality of these results. This study's insights are expected to contribute to further research aimed at optimizing charging conditions for tube skids and other hydrogen tanks. hydogen tank; hydrogen filling; environmental condition; temperature distribution; numerical analysis +
Footnote †: journal: Applied Sciences  
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Footnote  
Currently, the prevalent hydrogen fuel technology involves compressing hydrogen to high pressures, approximately 350 to 700 bars, to address the issue of hydrogen gas's low density [4]. This results in high pressure changes in hydrogen tanks during charging, compared to other gas fuels such as compressed natural gas [5], and leads to rapid temperature increases within the tank due to the enthalpy rise from gas compression during the filling process. Recent advancements in high-pressure hydrogen tanks, for instance, type IV tanks, have incorporated composites with a limited operational temperature range for weight reduction [4]. Thus, ensuring the safe usage of hydrogen tanks necessitates the establishment of specific charging and discharging conditions by analyzing the temperature distribution within hydrogen tanks under various charging scenarios. Most previous studies on predicting temperature variations in hydrogen tanks have focused on fuel tanks for vehicles. For example, [PERSON] [6] analytically estimated the temperature change during the hydrogen refueling process in hydrogen fuel-cell vehicles using ideal gas equations and applied the reduced Helmholtz free energy to correct the inaccuracies of these equations at high pressures. Numerous studies have employed numerical methods to examine the temperature dynamics in hydrogen tanks designated for vehicle use, with a particular emphasis on rapid filling processes [7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. These investigations have explored the impact of various factors--such as state of charge, ambient temperature, charging duration, and tank geometry--on the temperature distribution within the tank throughout the charging procedure. Given that rapid filling typically occurs within a short period of a few minutes, some studies have modeled and analyzed the tank's complete three-dimensional (3D) structure [7; 8; 9; 10; 11]. However, due to the extensive computational resources and time required to analyze compressible fluids, other research has limited the analysis to either half of the 3D geometry [12] or a simplified two-dimensional (2D) axisymmetric representation of the tank [13; 14]. Notably, [PERSON] et al.