One-dimensional Numerical Heat Transfer Model for Type C Thermocouples

Unlike traditional thermocouples with small junctions (just welding points), the junction of a type C thermocouple is normally formed by winding one wire around another wire, forming a large and complicated thermocouple junction. The large junction results in an obvious temperature difference inside it, while the junction temperature can be assumed to be uniform for traditional thermocouples. The one-dimensional (1D) numerical model for traditional thermocouples should be modified for applications with type $\mathbf{C}$ thermocouples. An improved 1D model considering the junction temperature variation is presented here for type $\mathbf{C}$ thermocouples. The simulation accuracy of the 1D model is validated with the more accurate results of CFD simulations covering the conditions of gas temperatures $1700-2300 \mathrm{~K}$, gas velocities $5-15 \mathrm{~m} / \mathrm{s}$, and thermocouple wire diameters $\mathbf{0. 1 - 0. 5 ~ m m}$. The maximum error is less than 0.9%, and the analysis reveals that the accuracy of convective heat transfer coefficients causes the error.