The effect of instantaneous particle distributions on the gas-phase temperature in an unsteady particle-laden jet heated with high-flux radiation

Abstract

Detailed simultaneous planar measurements of particle number density and gas-phase temperature were performed in radiatively heated particle-laden jet with average particle volumetric loadings in the range 0.625−−1.4×10−3, which is within the transition region between the two- and four-way coupling regimes, to evaluate the correlation between the local particle volume fraction and temperature for inertial particles with a series of diameter distributions and radiative heating powers. Utilising novel optical measurement and image processing techniques, together with Voronoi analysis, regions of high instantaneous particle number density and localised regions of high/low gas-phase temperatures were identified. The results show that the particle volume fraction measured within the identified ‘hot regions’ was more than 1.5 times greater than the mean value for each case, while within the ‘cold regions’ the particle volume fraction was typically less than the mean. Similarly, the temperature around individual particles was found to increase with an increase in the local particle volume fraction, while the variation in local gas temperature in the vicinity of particles increases with a decrease in particle diameter. Furthermore, the temperature surrounding particles that were determined to be within closely spaced cluster regions (which form in the present measurements due to the random distribution of particles in the flow) was found to be greater than that around particles outside of clusters, even for the same local particle volume fraction (measured in a radius of 0.1 times the jet pipe diameter around each particle). The particle distributions were found to closely match a random Poisson distribution, consistent with the high particle Stokes numbers (86 ≤SkD≤ 514), and are not affected by the presence of radiative heating, implying that any flow phenomena induced by thermal gradients in the flow negligibly influence the particles in the near field of the jet for the conditions investigated here.