Numerical study on turbulent mixing of particles in crossflow

The mixing characteristics of spray droplets in the turbulent gas crossflow in a horizontal tube were numerically studied. The droplets were produced by the pressure swirl nozzles which were evenly mounted in the same cross section of the tube. Three parameters including the degree of mixedness, uneven concentration factor and non-dimensional particle concentration were proposed to assess the mixing effect. The curves of both degree of mixedness and uneven concentration factor along the crossflow and isoconcentration lines in different cross sections were plotted. The inter-impact of the crossflow and droplets under different conditions involving water/gas mass flow ratio, spray angle and droplet diameter were analyzed. The results show that different-scale eddies are generated due to the adding of droplets into the crossflow, leading to the increase of turbulence intensity. The droplets in the cross sections near the nozzles distribute unevenly due to the big eddies, which results in low degree of mixedness. However, the degree of mixedness increases rapidly along the crossflow and reaches a stable value at short distance from the nozzles. Meanwhile, the droplets tend to congregate in the near-wall region due to both the initial spray configuration and the tendency of particles' congregating in high strain and low vortex regions. A better mixing result can be obtained with water/gas mass flow ratio of 1:1, moderate spray angle of 90° and bigger droplet diameter.