## 3 Result and Discussions
### Analysis of Pressure Coefficient (\(C_{p}\)) and Velocity Results in L-Shaped Bend of Check Valve
The pressure coefficient tends to decrease at the boundary layer point between the flow-separation and the main flow region, but it is found that the pressure coefficient has a constant distribution as a result of flow stabilization due to the lack of significant change in flow velocity in the main flow region. In this case, the pressure coefficient increases by up to 98% at point X = 91.7 mm for the (T\({}_{\text{in}}\)) 233 K condition compared to the (T\({}_{\text{in}}\)) 363 K condition. This can be explained by the fact that as the hydrogen-inlet temperature increases, the viscosity increases, which increases the flow-separation region and facilitates the reattachment of flows that have dropped out of the boundary layer. By analyzing the pressure coefficient results, the flow-separation region was formed to understand the effect of flow separation and reattachment at the boundary layer on the pressure change. In addition, the mixing of reverse flow and wake caused by recirculation flow appears to cause flow reattachment and delayed pressure recovery due to energy loss within the boundary layer. In order to understand the effect of the energy loss due to the flow-separation phenomenon on the change of flow characteristics in the discharging part, the temperature result graph in the Y-axis direction is shown in Figure 7. Hydrogen, which has the physical property of a reverse Joule-Thomson coefficient, increases in temperature due to the Joule-Thomson effect in regions where the pressure decreases and the volume expands [29], resulting in a localized decrease in temperature as hydrogen is expelled from the L-shaped curved tube region to the discharging part. As the X-axis measurement position changes to the back end, the temperature distribution in the Y-axis direction shows a localized increase in the upper part of the valve, while the temperature decreases in the lower part of the valve. If the hydrogen enters at (T\({}_{\text{in}}\)) 363 K in the region where the flow rate of hydrogen is reduced and flow separation is identified as occurring, the temperature of the hydrogen will increase by up to about 4 K compared to the entering temperature of the hydrogen, but the temperature difference will be up to (T\({}_{\text{in}}\)) 7 K at the bottom of the valve where the flow rate increases in the direction of the main flow. It is judged that the flow velocity increases due to the phenomenon of the vena contract, which reduces the flow area of the main flow due to the occurrence of flow separation in the L-shaped curved tube area, and the pressure decreases, resulting in a decrease in temperature due to the Joule-Thomson effect. Figure 5: Velocity_u results at X-axis measurement position. (**a**) X = 90.7 mm; (**b**) X = 91.7 mm; (**c**) X = 92.7 mm; (**d**) X = 93.7 mm; (**e**) X = 94.7 mm; (**f**) X = 95.7 mm. Figure 6: Normalized pressure coefficient results at X-axis measurement position. (**a**) Tin = 233 K condition; (**b**) Tin = 293 K condition; (**c**) Tin = 363 K condition. Analysis of Turbulent Dissipation Rate (TDR) and Exergy Destruction Results at Check-Valve Part Location  
To characterize the conversion of turbulent kinetic energy into internal thermal energy within the check valve, the turbulent dissipation rate (TDR) and temperature results were  
The graph of temperature results at the x-axis orientation measurement position in Figure 9 shows a correlation of increasing temperature at points where the TDR increases. The temperature results at X = 95 mm, where the TDR increases the most, show a maximum increase of about 4.5 K compared to the inlet temperature for a differential pressure (\(\Delta\)P) of 10 MPa and an inlet temperature (T\({}_{\rm in}\)) of 233 K. For all inlet temperature conditions, the temperature tends to decrease from X = 100 mm to X = 110 mm. The hydrogen discharged to the discharging part, which has a constant distribution with a gradual decrease in TDR, has an increasing distribution from the point X = 115 mm.