Numerical investigations of the lateral heat transfer in coaxial thermocouples

Abstract

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, due to the material difference between the two electrodes and the junction, lateral heat transfer occurs, 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 transfer effect has to be investigated to improve the accuracy and reliability of heat flux measurements. In this article, 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. During the heating process, the maximum temperature point on the surface of the coaxial thermocouples moved to the positive electrode over time. 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. The results of this study can provide a reference for the design and manufacture of coaxial thermocouples.