## 3 Results and Discussion
### Prediction Performance of Three Models for the Liquid Hydrogen Release  
Figure 6 shows the computed and experimental hydrogen concentrations at radii of 30, 50, and 100 m, and heights of 0.1, 1.0, and 1.8 m, considering a smaller leaked mass flow rate (\(\dot{\rm m}\)) of 0.225 kg/s. The black inverted triangular symbol represents the experimentally obtained time-averaged hydrogen concentration and the fluctuation bar indicates the maximum and minimum limits of concentration variation over time for the experimental concentration. The computed concentrations remained relatively constant, while the experimental concentrations exhibited significant fluctuations over time, as previously mentioned in Figure 5.  
Figure 4: Schematic of locations where hydrogen concentrations were measured. \begin{table}
\begin{tabular}{c c c c c} \hline
**Grid for Region II** & **0.2 m** & **0.3 m** & **0.5 m** & **1.0 m** \\ \hline Total number of grids & 1,576,440 & 713,934 & 328,328 & 150,144 \\ \hline Computation time & & & & \\ (wall clock time) & 132 h & 76 h & 52 h & 48 h \\ \hline \end{tabular}
\end{table} 
Table 3: Grid sizes and computation times. For the locations of R30/E and R50/E, slightly offset from the wind direction, it can be observed that the computed values from all models were nearly identical, and these computed values were close to the lower limits of experimental concentrations. For the R30/EN location, the pseudo-source model (\(\chi\) = 1.0) and hybrid model (\(\chi\) = 0.6) overestimated the experimental concentration, while the computed concentration by the liquid pool model (\(\chi\) = 0.0) relatively well matched the experimental values. For the R50/EN location, the results from the three models were in the range of experimental fluctuations, but the pseudo-source model predicts the highest hydrogen concentration, while the liquid pool model predicts the lowest. For R = 100 m, the computed results were similar to each other, and fell within the fluctuation limits of experimental concentrations. Figure 7 shows the computed and experimental temperatures of vapor clouds at radii of 30, 50, and 100 m for a case of m = 0.225 kg/s. For all locations, the temperatures computed by three models fell within the fluctuation limits of experimental temperatures. The computed results from the three models were very similar for all locations, except that the temperature computed by the liquid pool model was slightly lower than those from the other two models for the R30/EN location. Considering the results of Figures 6 and 7, it can be concluded that the liquid pool model performs better than the other two models for a smaller mass flow rate of m = 0.225 kg/s. Figure 5: Hydrogen mole fractions for different grid sizes at selected locations (grid sizes of 0.2, 0.3, 0.5, and 1.0 m for Region II, and at H = 1.0 m). Figure 6: Comparison of hydrogen concentrations computed by three models and those measured in the experiment at various locations for a case of \(\dot{\rm m}=0.225\) kg/s. Figure 8 shows the computed and experimental hydrogen concentrations at radii of 30, 50, and 100 m, and heights of 0.1, 1.0, and 1.8 m, considering a leaked mass flow rate of 0.73 kg/s. For all radii and heights, the hydrogen concentrations were similar for \(\chi=1.0\) and 0.6, whereas the concentration for \(\chi=0.0\) was lower than the results predicted by the other two models. At radii of 30 and 50 m from the leak source, the simulation results of the pseudo-source model and hybrid model closely matched the experimental concentration  
Figure 7: Comparison of temperature computed by three models and those measured in the experiment at various locations for a case of m = 0.225 kg/s. near the time-average value. However, the computed concentrations for \(\chi\) = 0.0 were closer to the minimum limits of experimental concentrations at distances of R \(\leq\) 50 m. When considering locations at R \(\leq\) 50 m with various directions, the results computed by all three models demonstrated reasonable prediction performance.