On the Measurement Error of Temperature in Nanocomposite Thermal Insulation by Thermocouples

The nanocomposite thermal insulation (NTI) has been found excellent potential application in various high-temperature engineering fields such as thermal protection of hypersonic vehicle, energy storage and thermal utilization. Whether in thermal property measurement or thermal behavior and performance experiment on this kind of material at high-temperature, the measurement of temperature inside the nanocomposite is necessary. For the low thermal conductivity of the nanocomposite thermal insulation, however, the measurement error can be caused by the local temperature gradient around the thermocouple node. But this issue has not been investigated before to our knowledge. In this paper, the error of temperature measurement inside the nanocomposite thermal insulation is investigated by numerical simulation. The nanocomposite thermal insulation is modeled to be an absorbing and emitting semitransparent medium, and a thermal couple node is located inside the medium with thermal conduction to surroundings by wires. The transient coupled heat transfer of radiation and conduction in the medium, and the transient heat exchange of thermal couple node with the medium by conduction and radiation as well as by wire conduction are considered during the temperature measurement. The finite volume method (FVM) combined with the Monte Carlo ray tracing method (MCRTM) is employed to solve the transient temperature field in the medium. For various heating conditions, the temperature fields inside the medium slab with and without the thermal couple were analyzed. By comparing the transient temperature responses of the thermocouple and the medium grid where the thermal couple node located, the effect of the diameter of the thermocouple node on the measurement error is investigated. The results show that the thermocouple node diameter exerts significant effect on the measurement error, and the error reduces greatly with the thermocouple diameter decrease.