Influence of thermocouple angles and wire distance on temperature measurement

Abstract

When a thermocouple is used to measure gas temperature, the measured temperature, i.e., the thermocouple bead temperature, is not equal to the gas temperature. The bead temperature results from the bead energy balance. The positioning angles such as the pitch angle and the roll angle and the wire distance of the thermocouple will influence the convection heat transfer of the thermocouple, causing the bead temperature variation. Two S type thermocouples are used to measure the temperature of the H2/air Hencken flame with the equivalence ratio 0.7. The maximum measurement temperature changes are 52 K and 79 K for the pitch angle variation and the roll angle variation, respectively. CFD simulations are carried out to simulate the experimental phenomena. The differences between the simulated and measured bead temperatures are less than 20.4 K. With 90° roll angle, the bead temperature increases first then decreases with the pitch angle. With 90° pitch angle, the bead temperature increases first then decreases with the roll angle. With 0° pitch angle, the bead temperature increases monotonically with the wire distance. The background physical mechanisms of the phenomena are analyzed with the detailed CFD results.