In order to realize accurate dynamic control of supersaturation and to study condensation growth characteristics of nanoparticles through different levels of supersaturation, a series of parametric analyses and systematic comparisons between two-stage and three-stage operating temperature designs were simulated with COMSOL Multiphysics. The simulation results showed that the three-stage operating temperature did not change peak supersaturation compared with two operating temperatures, and the three-stage operating temperature was superior in decreasing the amount of water vapor and the temperature, thus lowering particle loss and variation in detection and collection. The peak supersaturation level increased by 0.3 as the flow rate increased from 0.6 to 2.0 L/min, but the supersaturation peak moved from 0.0027 z0 to 0.08 z0 (i.e., the growth time and the final size decreased by 40%). Peak supersaturation increased as the temperature difference increased or the temperature difference window was shifting left, and minimum activation size decreased. Shifting the 70°C temperature difference window from 9°C, 79°C-1°C, 71°C for the condenser and initiator temperatures resulted in peak supersaturation in the centerline being above 5.8, and the activation size changed as low as 1 nm. Experiments with flow rates varying by a factor of 2.5 (from 0.6 to 1.5 L/min) resulted in a final size decrease of 43% (from 3.2 to 1.8 μm), and experimental results of outlet particle size distributions were equivalent with theoretical analysis as the operating temperature was changed.
Keywords: Flow rate; Minimum activation size; Operating temperature; Supersaturation profile; Temperature difference.
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