## 3 Results and Discussion
### Influence of Working Pressure  
In this part, the benchmark case is under a mass flow rate of 1 g/s, the \(T_{psi}\) is at 373.15 K, 473.15 K, 573.15 K, and 673.15 K, and the working pressure is reduced from 5 MPa to 3 MPa and increased from 3 MPa to 5 MPa. As shown in Figure 17, the fuel temperature was more sensitive than the wall temperature under varying working pressure conditions. With a decrease in the working pressure, the fuel temperature experienced a decrease-increase-decrease process, whereas the wall temperature showed a decreasing trend. The fuel and wall temperatures under the increasing working pressure condition are in contrast to the decreasing working pressure condition. In addition, with a decrease in the working pressure, the stable temperature increased compared to the initial time. The stable temperature increased by nearly 12 K compared with the initial time when the \(T_{foi}\) was approximately 673.15 K.  
As shown in Figure 18, the trend of the overall heat transfer coefficient changed on a small scale and fluctuated only in the initial stage of the response. With a decrease in pressure from 5 MPa to 3 MPa, the overall heat transfer coefficient increased with \(T_{foi}\). The overall heat transfer coefficient shows a decreasing trend when the \(T_{foi}\) is 373.15 K, 473.15 K, and 573.15 K. Furthermore, when the increase in \(T_{foi}\) is higher, the decrease in the heat transfer coefficient is larger. The overall heat transfer coefficient shows a sharply increasing trend and then sharply decreased and approached a stable value when the \(T_{foi}\) was approximately 673.15 K. When the pressure was increased from 3 to 5 MPa, the stable value of the overall heat transfer coefficient increased. However, the increase in pressure has little effect on the overall heat transfer coefficient at a \(T_{foi}\) of 373.15 K and 473.15 K. The overall heat transfer coefficient shows an upward trend at the beginning of the response and then approaches a stable value at \(T_{foi}\) = 573.15 K. At \(T_{foi}\) = 673.15 K, the overall heat transfer coefficient first decreased sharply, then increased sharply, and then decreased slowly. The difference between the inner wall temperature and the fuel temperature of the adjacent wall is shown in Figure 19. When the fuel pressure was 3 MPa, the temperature difference increased with the increase in \(T_{foi}\). However, the temperature difference did not change significantly with a decrease in pressure during the entire response time. In addition, with a \(T_{foi}\) of 473.15 K, the partial derivative of the adjacent wall fuel temperature shows a slow downward trend; with a \(T_{foi}\) of 573.15 K, the trend is more apparent. At \(T_{foi}\) = 673.15 K, the partial derivative of the adjacent wall fuel temperature first increased sharply and then decreased slowly. At a pressure of 5 MPa, the temperature difference increased. This trend was more evident with an increase in \(T_{foi}\). The partial derivative of the adjacent wall fuel temperature does not change significantly with an increase in  
Figure 18: Change in the OHTC and SCHTC at X = 900 mm with working pressure changes. (**a**) 5 MPa to 3 MPa; (**b**) 3 MPa to 5 MPa. pressure; however, with an increase in \(T_{\mathit{f}gi}\), the partial derivative of the adjacent-wall fuel temperature shows an increasing trend. With decreasing pressure, the change in the surface convective heat transfer coefficient was caused by the partial derivative of the near-wall fuel temperature, which can be inferred from Figures 18 and 19. When the pressure increased, the \(T_{\mathit{f}gi}\) was approximately 373.15 K, and the surface convective heat transfer coefficient increased with the decreasing temperature difference. However, with an increase in \(T_{\mathit{f}gi}\), the surface convective heat transfer coefficient shows an increasing trend in the initial response.