Coaxial thermocouples have been widely used for transient heat transfer measurements in high-enthalpy shock tunnels. The one-dimensional semi-infinite heat conduction theory is typically used for temperature data processing. However, lateral heat transfer occurs due to material differences between the two electrodes and the junction, causing a deviation in the heat flux measurement from the prediction results of the one-dimensional semi-infinite heat conduction theory. Thus, the lateral heat conduction effect should be investigated to improve the accuracy and reliability of heat flux measurements. In this paper, the heat transfer in E-type (Chromel-Constantan) coaxial thermocouples was analyzed by numerically solving the two-dimensional axisymmetric heat conduction equation with the Du Fort-Frankel scheme. The maximum temperature point on the surface of the coaxial thermocouples shifted to the positive electrode during the heating process. The numerical simulation indicated that the surface temperature of the coaxial thermocouples and the derived heat flux were larger than the theoretical value. The heat flux measurement error of the coaxial thermocouples can be reduced by increasing the width of the positive electrode. Hence, 13 combinations of the diameters of positive electrode and negative electrode were designed for analysis. With the increase of positive electrode diameter or decrease of negative electrode, the heat flux measurement error kept on decreasing, which can be lower than 0.5% in some cases. The results of this study can provide a reference for the design and optimization of coaxial thermocouples.

同轴热电偶已广泛用于高焓激波隧道中的瞬态传热测量。一维半无限热传导理论通常用于温度数据处理。然而，由于两个电极和结之间的材料差异会发生横向传热，导致热通量测量与一维半无限热传导理论的预测结果存在偏差。因此，应研究横向热传导效应以提高热通量测量的准确性和可靠性。本文采用 Du Fort-Frankel 格式对二维轴对称热传导方程进行数值求解，分析了 E 型 (Chromel-Constantan) 同轴热电偶的传热。在加热过程中，同轴热电偶表面的最高温度点向正极移动。数值模拟表明同轴热电偶的表面温度和导出的热通量均大于理论值。通过增加正极的宽度可以减小同轴热电偶的热通量测量误差。因此，设计了13种正负极直径组合进行分析。随着正极直径的增大或负极的减小，热通量测量误差不断减小，在某些情况下可低于0.5%。本研究结果可为同轴热电偶的设计和优化提供参考。