Mechanisms of particle separation in aerodynamic air cleaning

The mechanisms of particle separation in the aerodynamic air cleaner were studied by using theoretical analyses, experimental investigations and computational fluid dynamics simulations. This technology was also applied in cooling air cleaning for the radiator of a combine harvester.; An analytical model was developed considering the converging region under laminar flow and complete mixing conditions. Parametric analysis showed that the particle separation efficiency increased with the inlet air Reynolds number, the geometry constant, and the particle density and diameter.; This model was experimentally validated using a laboratory prototype under three inlet air Reynolds numbers---Re = 9993, 17765, and 25581. The experiments were compared with the theoretical analyses and the Crawford model developed in 1976. It was found that the new model agreed with the experiments well, while the Crawford model under-estimated the particle separation efficiency. Nevertheless, the measured efficiencies for smaller particles were always lower than the predictions using the models. To investigate the low efficiency for smaller particles, the airflow pattern inside the identical prototype was characterized using a three-dimensional hotwire anemometer. It showed that the velocity variation within the straight region was much lower than in the dust bunker. Computational fluid dynamics (CFD) simulations also showed that the reentrainment of particles from the bunker contributed to the lower separation efficiencies for smaller particles.; This aerodynamic air cleaning technology was applied for cooling air cleaning for the radiator of a combine. Three prototypes were developed and evaluated in the laboratory and/or field. The pressure drops of these prototypes were less than 250 Pa, and the overall efficiency was in the range of 70--80%. Laboratory test results further confirmed that bunker design was critical for reducing particle reentrainment.; Systematic studies on the bunker were recommended. These studies could be conducted by comparing different physical models with the assistance of CFD simulations. In CFD simulations, user defined functions were strongly recommended for calculating the particle separation efficiency.