## 4 Conclusions  
To evaluate the transient flow and heat transfer characteristics of hydrocarbon fuel in the cooling channel, a modified overall heat transfer coefficient was used to characterize the dynamic process, and a two-dimensional calculation model was established. Subsequently, the transient flow and heat transfer characteristics of hydrocarbon fuels represented by n-decane were studied from the perspectives of variable inlet mass flow, heat flux, and working pressure. The conclusions are as follows. 1. Three dynamic working conditions for the cooling channel were proposed, considering the real working process of a scramjet. The modified overall heat transfer coefficient was adopted to characterize the dynamic flow and heat transfer process as precisely as possible, which helps in analyzing the heat transfer enhancement under dynamic working conditions. 2. In the variable inlet mass flow process, the stable time for the fuel temperature increased with a decrease in the inlet mass flow. In addition, near the quasi-critical temperature zone, the outlet velocity increased with a decrease in the inlet mass flow. It can be observed that there is an overshoot of the OHTC at the beginning of the fuel mass flow increasing the working conditions, which implies that the increase in fuel mass flow can enhance heat transfer in the cooling channel. 3. In the variable heat flux process, the stable time for the fuel temperature increased with a decrease in the heat flux. In addition, without heating, the stable time required for the outlet fuel temperature to decrease to room temperature at different \(T_{\mathit{f}gi}\) values is almost the same (approximately 12.5 s). There is also an overshoot of the OHTC at the beginning of the heat-flux-increasing working conditions because of the thermal acceleration of the fuel bought by the heat flux in the cooling channel. 4. In the process of variable working pressure, the fuel temperature was more sensitive to changes in the working pressure than to the wall temperature. In addition, with a  
Figure 19: Dynamic process of inner wall temperature and adjacent wall fuel temperature difference and the partial derivative of fuel temperature. **(a)** 5 MPa to 3 MPa; **(b)** 3 MPa to 5 MPa. change in pressure, the trend of the overall heat transfer coefficient changed slightly and only fluctuated at the initial stage of the response. 5. The dynamic flow and heat transfer processes of hydrocarbon fuels in cooling channels were also studied. The heat transfer characteristics were discussed using a modified heat transfer coefficient calculation method. Based on this, a suitable heat transfer correlation for the dynamic flow and heat transfer process was determined, which may provide a better understanding of the dynamic heat transfer process. Conceptualization: G.L. and H.L. ; methodology: H.L. ; validation: G.L., Q.X. and Y.F. ; formal analysis: G.L. and H.L. ; data curation management: Q.X. ; writing--original draft: G.L. and Y.F. ; writing--review and editing: G.L., Q.X., H.L. and Y.F. All authors have read and agreed to the published version of the manuscript. This research was funded by GuangDong Basic and Applied Basic Research Foundation (2022A1515110605), the Postgraduate Education Innovation Project of Guangdong Ocean University (202257), the Zhanjiang Marine Youth Talent Innovation Project (2021E05013), and the Guangdong Provincial Colleges and Universities Engineering Technology Center (2023 GCZX004). Not applicable. The raw data supporting the conclusions of this article will be made available by the authors on request. The authors thank the reviewers for their valuable advice on this study. The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analysis, or interpretation of the data; in the writing of the manuscript; or in the decision to publish the results. The authors thank the reviewers for their valuable advice on this study. The authors declare no conflicts of interest.