Abstract
A numerical and experimental investigation comparing two configurations for a slit nozzle virtual impactor, one using a three-partitioned horizontal inlet and the other using a typical vertical inlet, was conducted to improve collection efficiency and reduce wall loss. All parameters, such as the length and width of the acceleration nozzle, the width of the collection nozzle, the distance between the two nozzles, and the inlet flow rate, were kept constant, and only the inlet configuration was changed. The ratio of the minor to the total flow rate was fixed at 0.1. Parametric analysis was performed to study the flow-rate influence of incoming clean air and aerosol on the performance of the three-partitioned horizontal inlet virtual impactor. The square root of the Stokes number, (Stk)1/2, was used to characterize the collection efficiency and wall loss of both configurations. It was observed that by using the three-partitioned horizontal inlet, the cut-off diameter was reduced from (Stk)1/2 = 0.80 to (Stk)1/2 = 0.41, and the wall loss near the cut-off diameter decreased from 25%–45% to below 4.5%. Moreover, using the three-partitioned horizontal inlet reduced the contamination by particles smaller than the cut-off size in the minor outflow section of the virtual impactor to almost 0%.
Highlights
Inertial impactors, because of its simple design and operation, are widely used for separation of aerosol particles by their sizes
It was observed that the flow rate combination 2–3–4.1 has shown small cut-off diameter, low wall loss, and zero collection efficiency for particles smaller than the cut-off diameter
As the inlet flow rate combination with Q1 < Q2 < Q3 has shown better results, analysis was performed for particles having diameters in the range of 0.1 to 10 μm for the values listed in Table 3, to get the best combination of inlet flow rates
Summary
Because of its simple design and operation, are widely used for separation of aerosol particles by their sizes. A lot of studies have been carried out for performance improvement of inertial impactors by changing its geometric configurations and operating conditions, such as nozzle position, dimensions, and aerosol flow rate (Marple and Liu, 1974; Huang and Tsai, 2002a). The cut-off size of inertial impactors corresponds to the particle size, for which the collection efficiency is 50%. An ideal inertial impactor should have sharp collection efficiency curve. Huang and Tsai (2002b) used a porous substrate in inertial impactors to show the effect of Reynolds number and porous substrate resistance factor on the sharpness of separation efficiency curve. An ideal inertial impactor should have sharp collection efficiency curve. Huang and Tsai (2002b) used a porous substrate in inertial impactors to show the effect of Reynolds number and porous substrate resistance factor on the sharpness of separation efficiency curve. Jurcik and Wang (1995) showed the effect of impactor geometry
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