Thermal radiation, its effect on thermocouple measurements in the PANDA facility and how to compensate it

Abstract

Thermocouples are one of the most widespread used sensors for temperature measurements in several applications, thanks to their robustness, low cost and ease of installation. However, when used in high temperature environments or in the presence of flames or elevated hot sources, the measurement can be affected, for example, by radiative exchanges to and from the ambient. The focus of the present study is to experimentally assess the thermal radiation effect on the thermocouple measurements in a controlled environment. To do so, K-type thermocouples having different diameters (1 mm and 0.2 mm) and radiated homogeneously from all sides are used to measure the air temperature between 40 °C and 145 °C inside a black-body calibrator cavity. The experimental data are then used to implement and discuss an existing radiation correction framework, the reduced radiative error method (RRE). The results suggest to use smaller size thermocouples to reduce the errors associated with thermal radiation and improve the accuracy of the measurement. Additionally, the results show that the effect of thermal radiation is higher for larger size thermocouples, i.e. thermocouples with 1 mm diameter show an error of 1% in the range considered here. This error reduces by a factor of three when using thermocouples with 0.2mm diameter. This benefit needs to be ultimately balanced with engineering considerations – smaller sized thermocouples are more likely to break during positioning or experiments.