Temperature measurement of a burning surface by a thermocouple II

The measurement of surface temperature of a burning solid using microthermocouples was investigated experimentally and theoretically. The experimental investigation used ammonium perchlorate (AP). The theoretical investigation was based on a heat transfer analysis. Specifically, the error introduced due to heat conduction through the thermocouple leads was examined. The decrease in indicated surface temperature due to heat conduction through the leads was found to be as large as 100 K, depending on wire diameter, burning rate, and lead wire angle. An appropriate nondimensional parameter based on these variables is obtained for characterizing temperature error. In addition a significant finding was made with respect to the appearance or absence of a temperature plateau at the burning surface. Both the experimental and theoretical results show the absence of a plateau when the thermocouple bead emerges from the solid into the gas phase. This result is in contrast to the commonly assumed condition that the emergence of the bead is associated with a plateau in temperature, which has widely been used to identify the surface temperature.