## 3 Result and Discussions
### Analysis of Pressure Coefficient (\(C_{p}\)) and Velocity Results in L-Shaped Bend of Check Valve
In order to understand the effect of changes in flow characteristics such as hydrogen flow velocity and temperature changes caused by flow separation in the L-shaped curved tube region on the hydrogen flow at the back end of the valve, the pressure coefficient (C\({}_{\rm P}\)) results at the line measurement position were analyzed and are shown in Figure 6. Figure 6a shows the pressure coefficient (C\({}_{\rm P}\)) results at a hydrogen-inlet temperature (T\({}_{\rm in}\)) of 233 K, Figure 6b shows the results at a hydrogen-inlet temperature (T\({}_{\rm in}\)) of 293 K, and Figure 6c shows the results at a hydrogen-inlet temperature (T\({}_{\rm in}\)) of 363 K.  
For all inlet temperature (T\({}_{\rm in}\)) conditions, as the flow moves from X = 90.7 mm to X = 95.7 mm, the pressure coefficient decreases sharply at X = 91.7 mm, followed by a similar trend of increasing pressure coefficient (C\({}_{\rm P}\)) up to X = 94.7 mm and then decreasing at X = 95.7 mm. For the (T\({}_{\rm in}\)) 233 K condition, the pressure coefficient (C\({}_{\rm P}\)) at the point X = 95.7 mm compared to the point X = 90.7 mm shows a difference of 613.3%, the pressure coefficient (C\({}_{\rm P}\)) at the 293 K inlet temperature (T\({}_{\rm in}\)) condition shows a difference of 114.05%, and the pressure coefficient (C\({}_{\rm P}\)) at the (T\({}_{\rm in}\)) 363 K condition shows a difference of 63.76%, indicating that the change in pressure coefficient (C\({}_{\rm P}\)) tends to be less as the inlet temperature increases. In this case, under all inlet temperature conditions, the point where the pressure coefficient (C\({}_{\rm P}\)) decreases towards the rear of the measurement position tends to increase in the direction of the (\(-\))Y-axis, but the pressure coefficient increases from the point of Y = about 2.3 mm to the point of 1.5 mm, and a pressure recovery phenomenon occurs. This is thought to be due to wall flow reattachment within the flow-separation region, which reduces the flow velocity and allows the pressure to recover. In this case, due to the wake and recirculation flow caused by the flow reattachment within the flow-separation area formed at point X = 90.7 mm, the flow-separation area expands towards the rear of the valve, deflecting the flow toward the bottom of the valve, and the point where the pressure coefficient (C\({}_{\text{P}}\)) decreases increases in the (\(-\))Y-axis direction as the measurement position is located at the rear. For all inlet temperature and differential pressure conditions, the pressure coefficient results increase in the direction of the bottom of the valve, and the pressure coefficient results for the change in measurement position from X = 91.7 mm to X = 95.7 mm have a decreasing distribution compared to the point X = 90.7 mm. This is thought to be due to the effect that when hydrogen enters the L-shaped curved tube, the flow direction changes, causing stagnation of the flow, which locally reduces the flow velocity and increases the pressure. The low distribution of pressure coefficient results at the boundary layer of the valve surface is due to flow delamination, which causes fluid to move away from the wall, creating near-vacuum conditions in some of these regions, resulting in reduced pressure coefficient results. In addition, the pressure coefficient in the flow-separation region increases towards the bottom of the valve but decreases locally at the boundary layer of the main flow region, where the flow rate increases and then increases. This indicates that pressure changes occur due to irregular changes in flow velocity caused by reverse flow from the recirculation area to the flow-separation area. In addition, it is believed that the flow that has separated from the boundary layer does not reattach and forms a low-pressure region relative to the free flow region, resulting in no pressure recovery.