Paper Thermocouple correction method evaluation for measuring steady high-temperature gas

When a thermocouple is used to measure a high-temperature gas flow, the measured temperature, i.e., the thermocouple bead temperature is not exactly the gas temperature. The bead temperature results from its energy balance. A few correction methods have been developed to fix the well-known error. However, the accuracy of the correction methods were not well validated because of the lack of a high temperature gas source with known temperature. The Hencken flame generates a near adiabatic combustion product and its temperature, composition and velocity can be calculated accurately. The S type thermocouples with different sizes are used to measure the Hencken flame temperature. With both the gas temperature and the measured temperature are known, the accuracy of the correction methods are evaluated. It is found that the 1D numerical correction method gives the best accuracy. The extrapolation method and some correction equations also give reasonable accuracy. Some correction methods need accurate thermocouple emissivity. With the CFD simulation of the detailed measurement process of the thermocouples, the emissivity is extracted. The advantages and disadvantages of different correction methods in practical measurements are also discussed.