Modification of Preferential Concentration by Strong Radiative Heating

Particle clustering affects macroscopic heat transfer rates in systems such as spray burners, pulverized coal furnaces, biomass reactors, and particle-solar receivers. This process is often conceptualized as unidirectional: turbulent eddies determine the instantaneous particle distribution which subsequently impacts local heat transfer rates to the fluid. This work explores strong coupling regimes where heat transfer due to particles has a feedback effect on the underlying turbulent flow. Experiments are performed on a particle-laden jet exposed to high intensity radiation. A square duct at a Reynolds number of 10,000 laden with small Nickel particles at mass loading ratios up to 200 percent issues into an isokinetic co-flow and is exposed to 5 kW of near infrared radiation using a laser diode array. Mean gas temperature measurements within the jet show an average increase of 200 ^oC at the highest loading conditions. Instantaneous temperatures within particle clusters are expected to be higher. Particle positions and velocities are measured using high resolution imaging and particle image velocimetry. When subjected to radiative heating, both particle velocity fluctuations and the degree of preferential concentration decrease. The roles of variable property effects, dilatation of the gas within clusters, and buoyancy mechanisms are investigated using scaling analyses and directional measures of preferential concentration.