RESUMO
The use of thermally assisted fluorescence (THAF) for temperature measurements has been investigated in a laminar, premixed C(2)H(2)/O(2)/Ar flame seeded with Ga atoms. Average temperature measurements were made with an uncertainty of less than +/-100 K in flames >2150 K and were found to be in agreement with sodium line reversal temperature measurements and equilibrium calculations. In both fuel rich and lean flames spanning equivalence ratios from 0.75 to 2.0, it was found that composition influenced the measured temperatures, resulting in an accuracy of +/-100 K over this range of flame conditions. Dilution of the flame with N(2) rather than Ar resulted in measured temperatures that were substantially higher than the calculated adiabatic flame temperature, indicating that, in this case, a partial Boltzmann equilibrium is not established among the collisionally populated levels of Ga used for the measurement. These results indicate that THAF with gallium as the thermometric species is limited to cases in which an inefficient quencher, such as a rare gas, is the primary diluent.
RESUMO
Particle size measurements have been made of silica formation in a counterflow diffusion flame reactor utilizing dynamic light scattering and angular dissymmetry methods. The results suggest that the techniques compare quite favorably in conditions of high signal to noise. However, the dynamic light scattering technique degrades rapidly as the signal strength declines, resulting in erroneously small particle diameters. As a general rule dynamic light scattering does not seem to possess the versatility and robustness of the classical techniques as a possible on-line diagnostic for process control. The drawbacks and limitations of the two techniques are also discussed.
