# Analysis of Hydrogen Filling of 175 Liter Tank for Large-Sized Hydrogen Vehicle
## 3 Result and Discussion
### CgH\({}_{2}\) Behaviors  
A certain quantity of hydrogen gas remains in the hydrogen tank, such that the fuel tank of the vehicle is refueled with residual fuel in it. The pressure of the remaining gas influences the maximum temperature rise during refueling. In addition, the ambient temperature can be influenced by the hydrogen state in the tank. Therefore, in the present study, numerical parametric studies of CGH\({}_{2}\) behavior in a hydrogen tank during its filling for the 175 L tank were conducted with validated numerical method under different ambient temperatures and initial SOC pressure conditions, as shown in Table 3. The initial SOC pressure and ambient temperature conditions were 5-35 MPa (7-50%) and 243-313 K, respectively. Calculation of the filling process for the present simulation was proceeded until tank pressure reached the final pressure of 70 MPa. The representative velocity vectors at 50 s under 5 MPa and 243 K from commencement of filling are illustrated in Figure 3. Gas velocity and velocity gradients are found to be highest in the vicinity of tank axis. It is observed that the incoming jet strikes the bottom of the tank, and flow turns along the surface toward the inlet, forming a secondary flow region on either side of inlet jet. Flow velocity gradually decreases with increase in pressure, as density of gas increases as the tank is filled up. Figure 4 shows the representative temperature contour of hydrogen filling at 40 s under 5 MPa and 273 K, and Figure 5 shows the time histories of the hydrogen gas pressure and temperature in the tank for the 5 MPa SOC pressure condition under different ambient temperature conditions of the tank at 243-313 K. The rate of pressure rise is shown with a constant increase phase for 400 s, after which the pressure rise rate decreases. Figure 3: Representative velocity vector (hydrogen filling at 50 s under 5 MPa and 243 K). Figure 4: Representative temperature contour of hydrogen filling at 40s under 5 MPa and 273 K.  
Figure 5: Time histories of hydrogen of average gas pressure (**a**) and temperature (**b**) distributions of filling process for 5 MPa SOC pressure condition under different ambient temperature conditions. The time to charge the hydrogen pressure to 70 MPa was from 586 s to 615 s under ambient temperature conditions of the tank from 243 K to 313 K. The gas temperature inside the tank increased dramatically at the beginning of charging. As the filling process continued, the rate of temperature rise decreased. Figures 6-8 show the time histories of hydrogen of average gas pressure and temperature in the tank for the 10, 20, and 35 MPa of SOC pressure conditions. The results of maximum temperature and time to fill up to 70 MPa under different ambient temperatures and initial SOC pressure conditions are summarized in Table 4. The average times to charge hydrogen up to 70 MPa were 600, 495, 191, and 148 s for 5, 10, 20, and 35 MPa, respectively. This means that the average charging time of hydrogen was from 600 s to 148 s for 7% to 50% SOC for the 175 L tank. As for the different ambient temperature effects of the hydrogen tank, a relatively large pressure increase rate was observed with decreasing ambient temperature conditions. Therefore, a relatively shorter time to reach a maximum of 70 MPa was observed under decreased temperature conditions. This indicates that the charging time was different under ambient temperature conditions. For the 5 MPa SOC pressure condition, the time to fully charge up to 70 MPa had a time difference of 29 s between ambient temperature conditions of 243 K and 313 K. A decrease in this time was observed with decreasing ambient temperature. Less time difference (17 s) was observed to fully charge hydrogen for a large SOC pressure condition of 35 MPa compared to the 29 s time difference with 5 MPa. With the different SOC conditions, the maximum temperature rise of the hydrogen tank when the pressure reached 70 MPa decreased as the initial SOC pressure increased.