On the Temperature Measurement Bias and Time Response of an Aspirated Thermocouple in Fire Environment

To examine the uncertainty of thermocouple temperature measurements, the present study uses numerical simulations and analytical solutions to investigate the heat transfer processes associated with double shield aspirated thermocouple. This study is divided into two parts. First, 3D CFD calculations for real geometries are performed to understand the flow characteristics of double shielded aspirated thermocouples. Based on iso-thermal flow calculations for real geometry, conjugate heat transfer calculations for a 3D simplified geometry are performed to investigate the thermocouple radiative exchange errors that may be important in a fire environment. The results of the 3D heat transfer calculation are compared with algebraic solutions from a previously developed simple energy balance model and the algebraic model shows acceptable results compared to the 3D CFD model, despite its many assumptions and idealizations. A parametric study was conducted to quantify the thermocouple errors for various gas temperature and surrounding conditions. In this manner, the present study improves our understanding of the uncertainty of thermocouple temperature measurements.