###### Abstract  
Regenerative cooling is critical for the thermal protection of hypersonic propulsion systems, wherein the flow and heat transfer characteristics of the hydrocarbon fuel in the cooling channel are crucial. Restricted by measurement, the distribution of the fuel temperature inside the cooling channel cannot be directly detected. As a result, the measurement of the convective heat transfer coefficient is more an overall heat transfer coefficient. Furthermore, the existing overall heat transfer coefficient calculation method is derived without considering the flow state of the hydrocarbon fuel in the cooling channel, which should be taken into consideration. Therefore, a modified calculation method of the overall heat transfer coefficient is proposed in this study. The  
heat transfer coefficient, much research has been conducted on it. [PERSON] et al. [9] obtained the convective heat transfer coefficient by calculating the average fuel temperature of a cross section. However, this method can lead to high errors, because the influence of the thermophysical properties of the hydrocarbon fuels near the pseudo-critical temperature was not taken into consideration. [PERSON] et al. [10] studied the influence of the dynamic viscosity on the convective heat transfer coefficient, but it was only applicable to turbulence, while the heat convection of the fluid was not considered. [PERSON] et al. [11], [PERSON] et al. [12], and [PERSON] et al. [13] went further by calculating the convective heat transfer coefficient in segments based on a ratio of the average temperature of a cross section in the critical temperature region. In addition, the thermophysical properties of the hydrocarbon fuel were adopted. However, the overall heat transfer coefficient calculated by piecewise convective heat transfer coefficient is bound to have a discontinuity point, which is derived from experimental data. [PERSON] et al. [14] proposed three calculation methods based on experimental data for the convective heat transfer coefficient in the laminar flow, transition flow, and the turbulent flow region, respectively. However, there was still a discontinuity problem when using three different calculation methods. [PERSON] et al. [15] assumed that there were two layers in the fluid. Based on this, the heat transfer process between the inner wall and the first layer of fluid was considered as the convective heat transfer. The first and the second layer of fluid were treated as the convective heat transfer, while the heat transfer in the layer of fluid was the heat conduction. However, this method only considered the influence of the heat conduction in the viscous bottom layer and did not consider the stratification of the velocity and temperature in the second layer of fluid. Therefore, the convective heat transfer coefficient calculated by the above method cannot be used to calculate the overall heat transfer coefficient.  
In this study, a modified calculation method of the overall heat transfer coefficient is proposed, and a numerical model is established. The characteristics of the overall heat transfer coefficient are discussed from a subcritical to a supercritical temperature region. The modified method is compared with the unmodified method. The results show that the overall heat transfer coefficient calculated by the modified method is smaller, which implies that the unmodified overall heat transfer coefficient might be overestimating the heat transfer enhancement process in the cooling channel.