Experimental study on the effect of particle size on the exit flow field of a swirl burner

• 1、Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Thermal Engineering, Tsinghua University

Abstract：Since the coal particles sent into the furnace of a boiler through the burner are of a size distribution and often vary in a certain size range during operation, understanding the particle size effect on the flow field is significant for burner design and operation. Experimental studies were carried out in a cold rig equipped with a swirl burner. The particle concentration field was observed by a CCD camera and the velocity field out of the burner exit was measured by a particle image velocimetry (PIV), under different seeding particle sizes. Experimental results show that the particle size can remarkably affect the gas-solid two-phase field outside the burner. The smaller particles easily follow the main gaseous flow stream and thus intensively mix into the secondary air and expand the main flow mixture with intensive turbulence. The larger particles, with larger inertia, more intend to keep the initial motion and are less influenced by the strongly swirling secondary air. On the other hand, the influence of solid phase of larger particles on the main flow stream becomes stronger when the particles pass through the swirling secondary air, reducing the swirling intensity of the secondary air. As a result, the recirculation zone becomes smaller, and its center moves further downstream. With the increment of particle size, both the axial velocity and the radial velocity slightly increase. Within the experimental circumstance, the effect on axial velocity is slightly stronger while expanding angle of the secondary air keeps nearly the same.

Keywords： multiphase flow particle size effect PIV measurement swirl burner exit flow field