## 3 Result and Discussions  
Analysis of Pressure and Velocity Results According to Inlet Temperature and Differential Pressure Change  
Figure 3 shows the in-valve pressure and flow results for the check-valve differential pressure (\(\Delta\)P) and hydrogen-inlet temperature (T\({}_{\text{in}}\)) conditions. The pressure change distributions in Figure 3a show that the pressure decreases locally in the nozzle neck region of the core part where the area of the flow path decreases rapidly, and the pressure has a constant distribution in the upper part of the core part where the area of the flow path increases, but the pressure decreases significantly as hydrogen is discharged to the discharging part. The results of the flow velocity change distribution for the flow direction in Figure 3b show that the flow direction changes to the (+)Y axis due to the inflow of hydrogen into the core part, and the flow velocity locally increases significantly in the nozzle neck region, where the flow area decreases sharply. The flow velocity decreases at the top of the core part, where the flow area increases, and the flow changes in the (\(-\))Y-axis direction. Hydrogen is discharged into the discharging part, and we can see that the flow changes in the X-axis direction through the L-shaped curved tube. At this time, it can be seen that the pressure decreases significantly in the L-shaped curved tube area and the flow rate tends to increase to the maximum. Also, the flow-separation phenomenon occurs, which diverts the flow to the lower part of the check valve. Figure 4a shows the pressure drop results from the flow-in part to the discharging part for the flow direction. In the flow-in part, before the hydrogen enters the core part, a pressure drop of up to 0.6 MPa occurs under the conditions of a 233 K hydrogen-inlet temperature (T\({}_{\text{in}}\)) and a 10 MPa differential pressure (\(\Delta\)P), and a pressure drop of up to 9.89 MPa occurs in the core part, where the area change of the flow passage occurs rapidly. The pressure-drop result at the discharging part shows that the pressure of hydrogen is recovered, and the pressure change due to the change in the area of the flow path at the core part location is considered to be the dominant influence on the pressure-drop result. Figure 3: \(Cont.\)Figure 4b graphs the pressure and flow velocity results at the measurement positions in the X-axis direction to analyze the overall flow characteristics inside the core part. It can be seen that the pressure decreases significantly at the 95 mm point, where the L-shaped curved tube that discharges hydrogen to the discharging part is located, and the pressure in the 95 mm region is reduced by up to 6% compared to the 90 mm region under the condition of 10 MPa differential pressure (\(\Delta\)P). The hydrogen discharged to the discharging part shows a local pressure increase after the X = 100 mm point of the plane and then shows a constant distribution, which is understood to be due to the stabilization of the flow of the discharged hydrogen due to the increase in the flow area of the discharging part and the lack of change in area, resulting in a constant distribution of pressure. The flow velocity results show a maximum increase in flow velocity at the 95 mm point where pressure drop is maximized and a decrease in flow velocity at the 100 mm point where hydrogen is discharged from the check-valve outlet. The difference in the maximum flow velocity at the 95 mm point under the differential pressure (\(\Delta\)P) 10 MPa condition was found to be up to 16% for the 363 K hydrogen-inlet temperature (T\({}_{\text{in}}\)) condition compared to the 233 K hydrogen-inlet temperature (T\({}_{\text{in}}\)) condition, indicating that the maximum flow velocity increases with increasing inlet temperature.