Effect of Thermal Radiation Heat Transfer on the Temperature Measurement by the Thermocouple in Premixed Laminar Flames

In the past 30 years, the effect of thermal radiation and convection heat transfer, which are predominant at high temperature and can affect the measurement accuracy of thermocouple, were not fully considered in the field of laminar flame researches. In this work, the effect of thermal radiation heat transfer was newly calculated by determining the spectral irradiation heat flux from the whole space to thermocouple and the radiation heat loss from thermocouple junction to surroundings. Analysis reveals that the thermocouple itself maintains at high temperature, resulting serious thermal radiation heat loss, which can be compensated via receiving energy from convection-transferred heat as well as thermal radiation emitted by flame and burner surface. Such method was applied to correct the temperatures measured by thermocouple in rich nitromethane flame as reference. The results indicate that the radiation heat loss plays a dominant role, while the radiations emitted by flame and burner surface account for minor contribution with the percentage of 20.78% at the height above burner(HAB) of 0.4 mm, 3.63% at HAB of 2.0 mm and even smaller at higher HAB. Temperature correction states that the maximum temperature error is 117.60 K, where the effect of thermal radiation emitted by flame and burner surface is less than 1.75 K. Consequently, it is provably reasonable and feasible to concentrate on the radiation heat loss and ignore the effect of thermal radiation emitted by flame and burner in real combustion processes.