On the response of coaxial surface thermocouples for transient aerodynamic heating measurements

• Published in: Experimental thermal and fluid science 2017-09, Vol.86, p.141-148
• Main Authors: Li, Jinping, Chen, Hong, Zhang, Shizhong, Zhang, Xiaoyuan, Yu, Hongru
• Format: Article
• Language: English
• Subjects: Aerodynamic heating; Calibration; Computer simulation; Conduction; Conduction heating; Conduction model; Conductive heat transfer; Fabrication; Gauges; Heat flux measurement; Heat transfer; Insulation; Mathematical models; Performance enhancement; Response characteristics; Shock tube; Studies; Testing time; Thermal properties; Thermocouple; Thermocouples; Thermodynamic properties; Thickness; Uncertainty
• ISSN: 0894-1777; 1879-2286
• DOI: 10.1016/j.expthermflusci.2017.04.011

•Response of a surface thermocouple closely relates to junction structure.•Insulation layer properties contribute a little to the response.•Reducing insulation layer thickness is effective to improve its performance.•Response of surface thermocouples was examined by a shock tube. Surface thermocouples are widely used in transient aerodynamic heating measurements, but their response often exhibits uncertainty and unpredictability, resulting in poor accuracy of measurement. To address this issue and provide reference information on their fabrication, the response of coaxial surface thermocouples was investigated numerically and experimentally. From the numerical simulations, it was observed that the heat blocking effect of the insulation layer can change the response of a thermocouple which strongly depends on the structure of the junction at short test times. Nevertheless, with increasing time, the response tends to be independent of the junction and be consistent with the prediction of the commonly used one-dimensional heat conduction model. Owing to the difficulty in controlling the junction, these observations not only account for the uncertainty and unpredictability of the response, but also suggest that for ensuring accurate measurements, a sufficiently long test time is necessary. The simulation also shows that the response of a thermocouple is insensitive to the properties of the insulation layer and that the duration of an uncertain response decreases dramatically with the thickness of the layer. To improve the performance of a surface thermocouple, additional effort should be directed at reducing the thickness of the insulation layer rather than enhancing its thermal properties. The shock tube experiments confirmed the achieved numerical results, and demonstrated a practical calibration technique for heat transfer gauges.