Validity evaluation on temperature correction methods by thermocouples with different bead diameters and application of corrected temperature

Accurate measurement of flame temperature by using bare thermocouples is a traditional and still a challenging problem. Three measurement methods, including the double- and triple-thermocouple correction methods and extrapolation method, have been developed to seek accurate gas temperatures, but the validity of these methods has been rarely evaluated for application in fire experiments. All the three methods use the temperature readings of multiple thermocouples with different bead diameters. This paper presents a systematic evaluation of validity for these methods by conducting fire temperature measurements. A turbulent propane pool fire was used. The temperatures along the fire plume centreline were measured at ten vertical heights of 10-55 cm, for which four thermocouples with different bead diameters were used at each height. Analysis shows that the flame turbulence imposes a significantly negative effect on the double- and triple-thermocouple correction methods. However, the extrapolation method can correct the fire gas temperature regardless of temperature pulsation related to flame turbulence. In addition, a new radiation model that incorporates the corrected flame temperature is proposed well against the radiant heat flux measurement. Moreover, it is found that the flame pulsation frequency can be roughly estimated by the temporal derivation of the corrected flame temperature.