A Dual-Parametric G-Type Coaxial Thermocouple With Superior Thermal Measurement Capabilities

In the context of hyperthermal aerodynamics, where the heat transfer rate changes rapidly, there is an urgent need to obtain thermal data on the surface of structures. To address this, we propose a novel G-type coaxial dual-parametric sensor that utilizes the Seebeck thermoelectric effect to measure the temperature of high-temperature airflows and derive heat fluxes based on the 1-D semi-infinite body assumption method. In a laboratory environment, we performed static calibration of the sensor’s performance indices in the temperature range of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$200~^{\circ }$ </tex-math></inline-formula>C–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1500~^{\circ }$ </tex-math></inline-formula>C. The calibration results of voltage versus temperature indicate that the sensitivity of the sensor is approximately <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$21~\mu $ </tex-math></inline-formula>V/°C, with a fitting coefficient exceeding 0.9999. Compared to the national standard for G-type thermocouples regarding the temperature-voltage relationship, the maximum voltage deviation is only 0.1 mV. Additionally, when we calibrated the heat flux of the sensor using a laser calibration method, the sensor monitored a heat flux upper limit of over 21 MW/m2, with an absolute error of less than 1.5%, corresponding to a heat flux response time of 1.15 ms. Finally, the G-type coaxial sensor, prepared using the natural growth method for the insulating layer, successfully achieved dual-parameter monitoring of structural surface temperature and heat flux exceeding <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1250~^{\circ }$ </tex-math></inline-formula>C and 5.1 MW/m2 in the high-temperature environment of supersonic flame washout. This provides a feasible solution for the accurate acquisition of structural surface thermal data in various rocket motor components.